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Abstract

This chapter summarizes the processes and effects of the most notable catastrophic mass movement events in South America in the twentieth century. We present 23 case histories of individual and regional landslide events, beginning at the northeast terminus of the Andes Mountains in Venezuela, proceeding counterclockwise down the Pacific Coast to the southern Andes of Chile and Argentina, and ending with discussion of catastrophic regional mass movements in the Brazilian Highlands.

The types of landslides involved in these disasters ranged from high-velocity rockslides and rock or debris avalanches to high- to medium-velocity debris flows and mudflows. Most casualties were caused by high-velocity debris avalanches and high-to medium-velocity, highly mobile, long-runout debris flows. A common, and particularly devastating, regional occurrence consisted of earthquake-triggered slides on steep slopes covered with saturated residual soils; these slides were rapidly transformed into very fluid, high-velocity debris avalanches, which in turn changed into devastating debris flows that ran out into populated areas on valley bottoms.

Introduction

The American Geological Institute's Glossary of Geology (Bates and Jackson, 1987, p. 104) defines a catastrophe as “A sudden, violent disturbance of nature, ascribed to exceptional or supernatural causes, affecting the physical conditions and the inhabitants of the Earth's surface…” Thus, a catastrophic landslide is one that is triggered by an exceptional process or cause and strongly affects (at least locally) the Earth's surface and its human and animal populations. In most cases, the causes of landslides are heavy precipitation, earthquakes, volcanic eruptions, human activity, or a combination of these (Wieczorek, 1996). These processes are most effective in causing landslides when they occur in areas of rugged, landslide-susceptible topography and geologic materials that are susceptible to failure.

In South America, conditions that lead to catastrophic slope failures occur most commonly in the rugged Andes Mountains of the northern and western parts of the continent and in the Brazilian Highlands (Fig. 1). Many parts of the Andes ranges are subject to precipitation that exceeds 1500 mm/yr (Fig. 2). In addition, as a result of subduction of the Nazca plate beneath the South American plate, the Andes are subject to high levels of seismicity (Fig. 3) and to volcanic activity as part of the Pacific “Ring of Fire.”

Figure 1.

General physiographic map of South America showing locations (black dots) of landslide events discussed in this chapter (after Time Incorporated, 1961, p. 237).

Figure 1.

General physiographic map of South America showing locations (black dots) of landslide events discussed in this chapter (after Time Incorporated, 1961, p. 237).

Figure 2.

Average annual precipitation in South America (after Brawer, 1991).

Figure 2.

Average annual precipitation in South America (after Brawer, 1991).

Figure 3.

Zones of seismic intensity in South America. Local intensity may be even greater than indicated by legend (after Centro Regional de Sismologia para America del Sur, 1985).

Figure 3.

Zones of seismic intensity in South America. Local intensity may be even greater than indicated by legend (after Centro Regional de Sismologia para America del Sur, 1985).

Because they are higher than the relatively uninhabitable tropical lowlands of central South America, the lower Andes and the Brazilian Highlands provide suitable sites for habitation. In Venezuela, Colombia, Ecuador, Chile, Bolivia, Argentina, and Brazil, these mountains and highlands support many large and small cities, towns, villages, and agricultural communities. Major landslides in populated areas often kill people and their livestock, and damage or destroy their homes and infrastructures.

In this chapter we summarize the processes and effects of the most notable twentieth century catastrophic mass movements in South America. The 23 case histories begin at the northeastern terminus of the Andes in Venezuela, proceed down the Pacific Coast to the southern Andes of Chile and Argentina, and end with discussion of catastrophic mass movements in the Brazilian Highlands. These histories are based on literature surveys and our personal experiences; we have studied or visited several of the sites. No attempt has been made to identify all twentieth century catastrophic landslides in South America. Many incidents of lesser impact than those presented here have been noted only in local newspapers, a source of information not readily available to us. Note that we have not presented a case history for Bolivia: although this mountainous country is subject to landslides, we have found no accounts of catastrophic landslides in Bolivia recorded in the literature.

Venezuela

Urban landslides in the hills of Caracas

Caracas, the capital of Venezuela (Fig. 1), is situated in a narrow valley surrounded by hills composed of weathered Jurassic-Triassic metamorphic rocks. The pressing need for housing at the outskirts of the city has resulted in the development of unstable hilly areas. Many cuts and fills have been constructed without an adequate understanding of the geology and behavior of the weathered rocks. Thus, every year the hills of Caracas are subjected to landslides, most of which are associated with heavy rainfall, mainly from May to October, that averages ~1000–1100 mm/yr. For papers dealing with causes, prevention, remedial measures, mitigation, educational programs, and legal aspects of the landslide problems in the Caracas hills, see Singer (1983) and Salcedo (1984, 1988).

From the socioeconomic point of view, landslide problems in Caracas can be divided into two groups: (1) slides in low-income “barrios” (Fig. 4; Jimenez Diaz, 1992), where property damage due to the slides commonly is not high because of low property values, but loss of life is high; and (2) slides in moderate- to high-cost residential areas (Fig. 5), where property values are high, but loss of life is low. The population of Caracas is ~3.5 × 106 people. According to FUNDACOM, the government body in charge of the barrios, residents of these “squatter” settlements constitute 77% of the total population of metropolitan Caracas (Jimenez Diaz, 1992).

Figure 4.

Landslide in area of low-cost urban housing in Caracas, Venezuela. Landslide was triggered by heavy rainfall and leakage of sewer drainage. Photo was taken in 1993.

Figure 4.

Landslide in area of low-cost urban housing in Caracas, Venezuela. Landslide was triggered by heavy rainfall and leakage of sewer drainage. Photo was taken in 1993.

Figure 5.

Homes in high-cost residential area of Caracas, Venezuela, that were destroyed on September 29, 1993, by rainfall-triggered landslide.

Figure 5.

Homes in high-cost residential area of Caracas, Venezuela, that were destroyed on September 29, 1993, by rainfall-triggered landslide.

Total property damage and loss of life due to landslides in Caracas over the past 20 yr exceed damage and loss of life for the well-known 1967 Caracas earthquake (Salcedo, 1982). Zuloaga (1995) estimated total landslide losses in Venezuela as $55 million (U.S.) annually. This amount represents ~0.55% of the Venezuelan national budget and 1.14% of the gross national product. Most of these losses occur in metropolitan Caracas.

An excellent example of a catastrophic landslide in Caracas is the September 29, 1993, landslide that completely destroyed seven expensive homes and a 150 m section of street in a high-cost residential area. This landslide caused no casualties, but residents had only a 15–30 minute warning in which to abandon their homes. The slide blocked the main access to the suburban development, adversely affecting 20,000 families. Total damage was estimated at $2 million (U.S.), and engineering remedial measures cost another $6 million. The slide originated in a fill that had been placed on phyllites and schists that dip toward the slope face. The site had been subject to preexisting stability problems. The cause of failure was heavy rainfall plus leakage of wastewater at the site.

The Caracas hills are generally composed of weathered quartz-mica schists and sericite phyllites or calcareous quartz schists with thin marble inclusions. The weathered rocks exhibit well-developed foliation, with very low shear strength along the foliation. The main causes of landsliding are as follows.

1. Urban developments are located on ancient landslides that are subject to reactivation due to construction of earthworks or to heavy rainfall.

2. Cuts are made in which foliation dips outward at an angle lower than the inclination of the cut slope (i.e., the dip surface “daylights” in the cut) (Salcedo, 1984).

3. Effects of natural weathering processes accumulate over time. In tropical areas, such as Venezuela, important changes in geomechanical properties of rocks have been observed within periods of 10–20 yr (Salcedo, 1990).

4. Effects of the special human activities in areas of very low-income housing can include poor people in these areas building their houses without sewage-disposal and drainage facilities. The sewage leaks into the subsoil, which increases pore pressures in the soil and contributes to alteration of the rock mass, including dissolution of calcium carbonate from the rocks (Salcedo, 1991).

Rio Linton debris flows, 1987

On September 9, 1987, an unusually heavy rainfall of 174 mm in <5 h occurred in the Rio Limon drainage north of the city of Maracay, 100 km west of Caracas, in Aragua State, Venezuela (Figs. 1 and 6). This heavy rain saturated the residual soils on steep slopes (commonly >40°), which triggered thin slips and slumps that were soon transformed into very rapid debris avalanches and debris flows. These debris flows resulted in the worst landslide catastrophe in the history of Venezuela: ~20 000 people returning from a weekend at the beach were trapped on several sections of the highway; many were killed by debris flows. The debris flows continued down to the city of El Limon and to the small towns of Cana de Azucar and El Progreso, destroying houses and killing or injuring people. The event damaged or destroyed ~1500 homes, 500 vehicles (Fig. 7), three bridges, and 25 km of roads; ~210 people were killed, 400 were injured, and more than 30000 people were temporarily stranded.

Figure 6.

Map showing area affected by September 9, 1987, Rio Limon debris flows, Venezuela.

Figure 6.

Map showing area affected by September 9, 1987, Rio Limon debris flows, Venezuela.

Figure 7.

Vehicles destroyed by September 9, 1987, Rio Limon debris flow, Venezuela.

Figure 7.

Vehicles destroyed by September 9, 1987, Rio Limon debris flow, Venezuela.

The characteristics of the Rio Limon debris avalanches and debris flows can be summarized from Elizalde et al. (1987), Salcedo and Vignali (1987), and Montes (1989) as follows.

1. The intense rain saturated the soil, causing thin, elongated, shallow slips or slumps (thickness <1.5 m) to occur on the upper parts of steep slopes in the Rio Limon watershed. This process continued until the residual soils had been stripped to the underlying gneissic bedrock.

2. As the saturated soil masses moved downslope, they soon were transformed into very fluid debris avalanches and then to debris flows.

3. The debris flows, including boulders, trees, and other vegetation, moved down stream channels, forming temporary natural dams or plugs that inundated some areas.

The area denuded by the landslides was ~140 ha. Based on an average thickness of residual soil of 1.4 m, the total volume of material removed from the upper Rio Limon basin has been estimated at 2 × 106 m3.

In spite of the catastrophic consequences of the 1987 Rio Limon landslides, it is interesting to note that other landslide events of greater magnitude have occurred in the past in this area. Audemard and De Santis (1987) noted one such deposit of pre-Columbian age with a volume of 10 × 106 m3, 5 times larger than that of the 1987 event.

Colombia

Nevado del Ruiz debris flow, 1985

Nevado del Ruiz, the northernmost active volcano in the Andes, located in the Central Cordillera of Colombia, 140 km west of Bogota (Figs. 1 and 8), underwent a minor eruption on November 13, 1985, triggering eatastrophic mudflows and debris flows (lahars) that killed more than 22 000 people and destroyed more than $212 million (1985 U.S. dollars) in property (Herd, 1986; Garcia, 1988; Voight, 1990; Mileti et al., 1991). The relatively small eruption of this volcano ejected materials that melted part of the glacial ice cap at the summit of the volcano, releasing a series of lahars that descended through steep, narrow river canyons at speeds as great as 50 km/h.

Figure 8.

Map of Nevado del Ruiz area, Colombia, showing distribution of debris flows and/or mudflows, tephra. and volcanic ash from 1985 eruption (after Voight, 1990).

Figure 8.

Map of Nevado del Ruiz area, Colombia, showing distribution of debris flows and/or mudflows, tephra. and volcanic ash from 1985 eruption (after Voight, 1990).

Major flows descended the eastern side of the volcano in the valleys of the Rios Azufrado, Lagunillas, and Guali (Fig. 8). The flows from the Rios Azufrado and Lagunillas merged about halfway down the mountain to form a larger flow that continued down the Rio Lagunillas valley onto a populated, gently sloping, alluvial fan and adjacent flood plain that extends along the eastern front of the mountains. The mudflow devastated the city of Armero (Figs. 8, 9, and 10; preemption population: 29000), built on the alluvial fan. More than 20000 people perished at Armero, most of them crushed or buried in their homes, and 5000 more were injured (Voight, 1990). The lahar in the Azufrado and Lagunillas valleys traveled as far as the town of Santuario, 80 km downstream from the volcano (Fig. 8). The lahar in the Guali valley flowed into the Rio Magdalena at the town of Honda, 85 km downstream from the volcano. In doing so, it moved boulders as large as small houses (Fig. 11).

Figure 9.

City of Armero. Colombia, following 1985 eruption of'Nevado del Ruiz and subsequent flooding by debris flows and/or mudflows. Most of city of 29 000 was covered by flows. (Photo by Steve Raymer, courtesy National Geographic Magazine.)

Figure 9.

City of Armero. Colombia, following 1985 eruption of'Nevado del Ruiz and subsequent flooding by debris flows and/or mudflows. Most of city of 29 000 was covered by flows. (Photo by Steve Raymer, courtesy National Geographic Magazine.)

Figure 10.

Business district in Armero, Colombia, showing effects of 1985 debris (low and/or mudflow. (Photo by R. Updike, U.S. Geological Survey.)

Figure 10.

Business district in Armero, Colombia, showing effects of 1985 debris (low and/or mudflow. (Photo by R. Updike, U.S. Geological Survey.)

Figure 11.

Large monzonite boulder on flood plain of Rio Guali, Colombia, was transported ~400 m by 1985 debris flow and/or mudflow. (Photo by R. Updike, U.S. Geological Survey.)

Figure 11.

Large monzonite boulder on flood plain of Rio Guali, Colombia, was transported ~400 m by 1985 debris flow and/or mudflow. (Photo by R. Updike, U.S. Geological Survey.)

Another lahar descended the western slope of the volcano through the narrow canyon of the Rio Chinchina (Fig. 8), destroying 400 homes and causing an estimated 1800 deaths near the town of Chinchina (Mileti et al., 1991).

In addition to the fatalities noted, lahars buried 3400 ha of agricultural land, and damaged or destroyed two hospitals, 50 schools, 5000 homes, 58 industrial plants, and 343 commercial establishments (Voight, 1990). In the region, 60% of the livestock, 30% of its grain sorghum and rice crops, and 500 000 bags of coffee were lost due to the flows and to volcanic ash, which blanketed the area northeast of the volcano.

The eruption of Nevado del Ruiz was not a surprise. The catastrophic loss of life was due in large part to failure of local authorities to plan and carry out an adequate emergency response to the threatened event. The disaster occurred in spite of the fact that Colombian and international scientists, alerted by nearly a year of precursory activity by the volcano, had warned that Ruiz might erupt. A hazard zoning map had been prepared that accurately predicted the tragic effects of the eruption weeks before it occurred (Voight, 1990; Mileti et al., 1991).

Similar lahars had occurred in the same valleys after eruptions of Ruiz in 1595 and 1845 (Mojica et al., 1986; Voight, 1990). Acosta (1846; translated and quoted by Voight, 1990, p. 350) provided a description of the 1845 event: “Then, descending along the Lagunillas from its sources in the Nevado del Ruiz, came an immense flood of thick mud which rapidly filled the bed of the river, covered or swept away the trees and houses, burying men and animals. The entire population perished in the upper and narrower parts of the Lagunillas valley.” Armero, which did not exist during these earlier disasters, was built on the site of these ancient mudflows (Voight, 1990).

Villa Tina landslide, Medellin, 1987

On September 27, 1987, the small, but sudden and disastrous, Villa Tina landslide (Fig. 1) occurred in lateritic residual soils overlying Tertiary metamorphic rocks on the outskirts of the city of Medellin, ~300 km northwest of Bogota, Colombia. Although the failure surface was at a depth in the soil of only 1–1.5 m and the total volume of slide material was only ~20000 m3, at least 217 people were killed and 80 houses were destroyed by the fast-moving slide (Tokuhiro, 1988).

Even though there had been no rainfall in the area for a considerable period before the disaster, the landslide mass contained water. It was concluded from the post-landslide investigation that water from a water-supply pond above the slide area had penetrated the preslide soil mass, causing the failure.

Landslides from the Paez earthquake, southwestern Colombia, 1994

On June 6, 1994, a M = 6.4 earthquake shook the Paez River drainage in southwestern Colombia, south of Nevado de Huila volcano (Figs. 1 and 12). During the earthquake, several villages in the drainage of the Rio Paez and its tributaries were destroyed, some by earthquake shaking, some by landslides (including earth flows, debris flows, and mudflows), and some by both (INGEOMINAS, 1994; Avila et al., 1995; Martinez et al., 1995). The earthquake and resulting mass movements caused 271 deaths; 156 people were injured, and ~1700 were reported missing (United Nations Department of Humanitarian Affairs, 1994). As of early July 1994, ~24800 people were still residing in 119 camps consisting mainly of plastic-covered shelters, and 7500 people were in temporary shelters and buildings; six bridges and 100 km of roads were destroyed by debris flows.

Figure 12.

Map of Rio Paez drainage, southwestern Colombia, showing locations of Nevado del Huila volcano and epicenter (star) of 1994 earthquake. Dashed line indicates outer limits of earthquake-triggered landslides (after Martinez et al., 1995).

Figure 12.

Map of Rio Paez drainage, southwestern Colombia, showing locations of Nevado del Huila volcano and epicenter (star) of 1994 earthquake. Dashed line indicates outer limits of earthquake-triggered landslides (after Martinez et al., 1995).

The Paez earthquake triggered landslides over an area of ~250 km2 in the Rio Paez basin (Fig. 12; Martinez et al., 1995). Almost all of the landslides originated as thin translational slides (~1–2 m thick) in saturated residual soils on steep slopes (=30°) underlain mainly by Paleozoic quartzite and schist. These thin slides were almost immediately transformed into either debris flows or earth flows as they moved rapidly down the steep slopes onto flatter slopes and into the Paez River and its tributaries. Locally, >50% of the valley slopes were denuded (Fig. 13). These debris flows and earth flows caused a major part of the damage due to the earthquake.

Figure 13.

Slides, debris avalanches, and debris flows on valley walls of upper Rio San Vicente (Fig. 12), southwestern Colombia, triggered by 1994 Paez earthquake. (Photo taken July 1994.)

Figure 13.

Slides, debris avalanches, and debris flows on valley walls of upper Rio San Vicente (Fig. 12), southwestern Colombia, triggered by 1994 Paez earthquake. (Photo taken July 1994.)

The largest flows followed the valleys of the Rio Paez and its largest tributaries, the Rio San Vicente and Rio Moras (Fig. 12), for a maximum distance of 120 km from the source area (Martinez et al., 1995). In the upper 35 km of the Rio Paez and its tributaries, the flows destroyed farms and villages located near the rivers (Figs. 14 and 15). In the downstream 85 km, the debris flows on the Rio Paez destroyed bridges and roads before dumping into Betania Reservoir on the Rio Magdalena.

Figure 14.

Massive debris flow entering Rio Paez near village of Irlanda (Fig. 12), southwestern Colombia. Homes and other buildings in lower right quarter of photo were destroyed by debris flow. (Photo taken July 1994.)

Figure 14.

Massive debris flow entering Rio Paez near village of Irlanda (Fig. 12), southwestern Colombia. Homes and other buildings in lower right quarter of photo were destroyed by debris flow. (Photo taken July 1994.)

Figure 15.

Home in village of Toez (Fig. 12), Rio Paez valley, southwestern Colombia, destroyed by debris flow triggered by 1994 Paez earthquake. (Photo taken July 1994.)

Figure 15.

Home in village of Toez (Fig. 12), Rio Paez valley, southwestern Colombia, destroyed by debris flow triggered by 1994 Paez earthquake. (Photo taken July 1994.)

Immediately after the disaster, it was generally thought that the large amounts of water that caused the thin slides to liquefy had come from the glaciers on Nevado de Huila volcano in a manner reminiscent of the 1985 lahars from Ruiz volcano. However, aerial investigation showed that there had been no melting of glaciers or snowpack during the event. Instead, the water in the flows was derived mostly from the residual soils, which were in a saturated state due to heavy rainfall in the weeks before the earthquake.

Ecuador

Chunchi landslide, 1983

On March 26, 1983, during the wettest year of the century, a major landslide occurred in the vicinity of the town of Chunchi, ~60–70 km north of Cuenca, on the western slope of the Andes in south-central Ecuador (Fig. 1). Although we have little information on this catastrophic mass movement, it involved ~1 × 106 m3 of geologic material that slid ~3000 m, blocked the PanAmerican Highway, buried vehicles on the highway, and killed more than 150 people (Torres, 1983; Benitez, 1989).

Landslides from the 1987 Reventador earthquakes, northeastern Ecuador

On March 5, 1987, two earthquakes (Ms = 6.1 and 6.9) occurred ~25 km north of Reventador Volcano in Napa Province along the eastern slopes of the Andes Mountains in northeastern Ecuador (Figs. 1 and 16). Although shaking from the earthquake damaged structures in towns and villages near the epicentral area, the economic and social losses directly due to shaking were small compared to the effects of catastrophic earthquake-triggered mass movements and flooding (Hakuno et al., 1988; Ishihara and Nakamura, 1987; Nieto and Schuster, 1988; Schuster, 1991; Tibaldi et al., 1995; Schuster et al., 1996).

Figure 16.

Area of mass wasting and flooding caused by 1987 Reventador earthquakes, northeastern Ecuador, indicating sections of damage to Trans-Ecuadorian oil pipeline and highway.

Figure 16.

Area of mass wasting and flooding caused by 1987 Reventador earthquakes, northeastern Ecuador, indicating sections of damage to Trans-Ecuadorian oil pipeline and highway.

In the month preceding the earthquakes, ~600 mm of rain fell in the region; thus, the surficial soils had high moisture contents. The average valley slopes in the Reventador area range from 35° to 45°. Before the 1987 earthquakes, the slopes were generally covered by residual soils of variable thickness and by a subtropical jungle. More than 90% of the slope failures caused by the earthquakes began as shallow slips or slides of residual soil and weathered volcanic rock on the uppermost slopes of main valleys (Fig. 17) or on slopes of lower order tributaries. These thin slides were almost immediately transformed into fluid debris avalanches and debris flows. The surficial soils and rock and the jungle vegetation covering them flowed down slopes into minor tributaries and then into major rivers (Salado. Quijos, Malo, Coca, Due, Due Grande, and Aguarico). Rock and earth slides, debris avalanches, debris flows, and mudflows, and resulting floods destroyed ~40 km of the Trans-Ecuadorian oil pipeline and the only highway (Figs. 16 and 18) from Quito to Ecuador's northeastern rain forests and oil fields. Estimates of the total volume of earthquake-induced mass wastage ranged from 75 × 106 m3 (Crespo et al., 1987) to 110 × 106 m3 (Hakuno et al., 1988; Okusa et al., 1989). Millions of tons of silty. gravelly sand, as well as remains of trees and other organic matter, were deposited in the rivers (Fig. 19). Economic losses were estimated at $1 billion (1987 U.S. dollars). The effects of widespread landslide denudation on the agricultural and hydroelectric development of the region were difficult to evaluate. but undoubtedly were large (Nieto and Schuster, 1988). Nearly all of the estimated 1000 deaths from the earthquakes were a consequence of mass wasting and flooding.

Figure 17.

1987 Reventador earthquake: aerial view of northeast valley wall of Rio Malo, northeastern Ecuador, showing extreme denudation of slopes due to slips, avalanches, and/or flows and of valley bottom due to debris flows and flooding. Note vegetation trimline in main valley that indicates maximum height of debris flow and/or flood. ~25 m above current river level. (Photo taken April 1987.)

Figure 17.

1987 Reventador earthquake: aerial view of northeast valley wall of Rio Malo, northeastern Ecuador, showing extreme denudation of slopes due to slips, avalanches, and/or flows and of valley bottom due to debris flows and flooding. Note vegetation trimline in main valley that indicates maximum height of debris flow and/or flood. ~25 m above current river level. (Photo taken April 1987.)

Figure 18.

1987 Reventador earthquake: aerial view is of destruction of Trans-Ecuadorian oil pipeline and adjacent highway by earthquake-triggered debris flow issuing from minor tributary of Rio Coca. (Photo taken April 1987.)

Figure 18.

1987 Reventador earthquake: aerial view is of destruction of Trans-Ecuadorian oil pipeline and adjacent highway by earthquake-triggered debris flow issuing from minor tributary of Rio Coca. (Photo taken April 1987.)

Figure 19.

1987 Reventador earthquake: aerial view of confluence of Rio Salado (lower left) and Rio Quijos (lower right) to form Rio Coca (flowing to upper left), northeastern Ecuador (Fig. 16). Post-earthquake, braided debris-flow and flood deposits are thick as 15 m in valley bottoms. Bedrock constriction (indicated by two white arrows) probably caused shortlived damming of river, which contributed to upstream flooding and rapid sedimentation. (Photo taken April 1987.)

Figure 19.

1987 Reventador earthquake: aerial view of confluence of Rio Salado (lower left) and Rio Quijos (lower right) to form Rio Coca (flowing to upper left), northeastern Ecuador (Fig. 16). Post-earthquake, braided debris-flow and flood deposits are thick as 15 m in valley bottoms. Bedrock constriction (indicated by two white arrows) probably caused shortlived damming of river, which contributed to upstream flooding and rapid sedimentation. (Photo taken April 1987.)

La Josefina landslide, 1993

On March 29, 1993, a massive rockslide dammed the Rio Paute, ~20 km northeast of Cuenca in the Inter-Andean Basin of south-central Ecuador (Figs. 1 and 20; Chamot, 1993; Canuti et al., 1994; Ortiz et al., 1994; Plaza-Nieto and Zevallos, 1994). This 20–25 × 106 m3 translational slide occurred in igneous rocks overlain by colluvial deposits. The slide was probably caused by heavy rainfall (March rainfall was approximately double the March average for the region) and by a 160-m-deep open-pit mine excavation at the base of the slope.

Figure 20.

Map showing location of La Josefina landslide dam. temporary Lago Josefina, and path of debris flow and/or flood down Rio Paute to Amaluza Dam (after Chamot. 1993; Plaza-Nieto and Zevallos, 1994).

Figure 20.

Map showing location of La Josefina landslide dam. temporary Lago Josefina, and path of debris flow and/or flood down Rio Paute to Amaluza Dam (after Chamot. 1993; Plaza-Nieto and Zevallos, 1994).

The regions upstream and downstream from the landslide were densely populated. Chamot (1993) estimated that 72 people were killed or missing due to the rockslide. Plaza-Nieto and Zevallos (1994) stated that 35 deaths were directly attributable to the landslide. The economic losses incurred by the landslide were devastating, as were the effects on the terrain and environment.

The slide formed a 100-m-high natural dam of the Rio Paute at its junction with the Rio Jadan (Chamot, 1993). The impoundment behind this dam flooded the upstream valley for a length of 10 km, submerging agricultural land, homes, and industries. The final stored water volume of the natural dam was 200 × 106 m3, corresponding to a depth of 83 m. After 33 days, the dam failed (Fig. 21), resulting in a peak discharge of 10000 m3/s. The resulting debris flow and mudflow flooded the valley downstream for a distance of 50 km. where, 3 h after failure of the natural dam, the flood entered Amaluza Reservoir, the impoundment behind Amaluza Dam. This dam is part of the Paute Hydroelectric Plant. which generates 65% of the electric power consumed by Ecuador. Before the landslide dam failed, the reservoir, which had a total capacity of 120 × 106 m3, was lowered 31 m to provide a storage volume of 51 × 106 m3 for the expected flood (Canuti et al., 1994). In spite of these precautions, the powerhouse turbines suffered damage due to high concentrations of suspended solids in the water.

Figure 21.

Failure of La Josefina landslide dam on April 26. 1993. Remnants of natural dam are near eenter of photo. Remnant of Lago Josefina is on Rio Paute on right in photo, and floodwaters exit in Rio Paute at lower left. Rio Jadan enters photo from left (photo courtesy of P. Chamot. United Nations Department of Human Affairs; Chamot. 1993).

Figure 21.

Failure of La Josefina landslide dam on April 26. 1993. Remnants of natural dam are near eenter of photo. Remnant of Lago Josefina is on Rio Paute on right in photo, and floodwaters exit in Rio Paute at lower left. Rio Jadan enters photo from left (photo courtesy of P. Chamot. United Nations Department of Human Affairs; Chamot. 1993).

The flood of debris caused very serious damage in the Rio Paute valley between the natural dam and Amaluza Reservoir. Hundreds of private homes and several industrial complexes on the Rio Paute plain were devastated. Because the flood was anticipated and people and livestock had been evacuated, the flood caused no casualties. While the water level was decreasing in Lago (Lake) Josefina because of failure of the landslide dam, several landslides occurred on the surrounding slopes due to the rapid drawdown; the most important of these was the Zhizhio slide, which occurred on the slope facing the original La Josefina failure.

The Josefina event is a prime example of the hazard presented by the formation of a natural stream blockage by a major landslide. Such natural dams occur frequently, and may cause catastrophic downstream flooding when they fail. In this case, a valiant effort was made to prevent failure of the landslide dam by excavation of a spillway channel across the natural dam. In 14 days, 160 000 m3 of material were removed, creating a channel with a base width of 6 m, depth of 18 m, and length of 407 m (Plaza-Nieto and Zevallos, 1994). Although the dam finally failed due to catastrophic erosion of the channel, this mitigative measure eliminated the certainty of the upstream flooding of an additional 250 ha of land and further accumulation of 130 × 106 m3 of water in the lake. If the channel had not been excavated, the peak discharge upon failure of the landslide dam would have been ~30 000 m3/s instead of the 10 000 m3/s that actually occurred, and would have resulted in an even greater catastrophe (Plaza-Nieto and Zevallos, 1994).

Peru

Huaraz debris flow, 1941

In 1941, a debris flow destroyed about 25% of the city of Huaraz (Fig. 1) in the Department of Ancash, Peru, killing an estimated 4000–6000 inhabitants (Bodenlos and Ericksen, 1955; Ericksen et al., 1989). The debris flow was caused by a sudden rupture of a morainal dam impounding a lake in the Cordillera Bianca northeast of Huaraz. The resulting debris flow, with a volume of at least 10 × 106 m3, swept 23 km down the Cohup Creek valley, through the northern part of Huaraz and into the Rio Santa. The debris flow temporarily dammed the Rio Santa. After two days, the dam overtopped and breached, and water and debris swept downstream to the coast, destroying settlements and farms in the valley of the Rio Santa.

This disastrous debris flow was the first major catastrophe to strike Huaraz in its 300 yr existence; however, it was only a prelude to catastrophes in the area in 1962 and 1970 (see following).

Rockslide of Cerro Condor-Sencca, 1945

On August 16, 1945, the large catastrophic Cerro Condor-Sencca rockslide dammed the Rio Mantaro in the Andes of Peru (Fig. 1). This 5.5 × 106 m3 slide, which originated in fractured granodiorite on the slope of Cerro Condor–Sencca hill in the Department of Ayacucho, formed a 100-m-high natural dam that impounded a lake 20 km long (Snow, 1964). The cause of the slide is not known, but it was probably a result of undercutting of the valley wall on the outside of a bend in the river. There were no witnesses to the slide, which occurred in a remote, unpopulated canyon. However, residents in the area noted a thunderous noise and earth tremors on the morning of August 16.

Because the site was unpopulated, the landslide caused neither casualties nor direct economic losses. However, after 73 days the dam failed by overtopping and erosion; after 7 h, the lake had drained and the dam material had been removed by traction. The flood (which was probably a debris flow) discharge exceeded 35 000 m3/s, 50 times the average annual maximum flood on the Mantaro. The velocity of the flood and/or debris flow was estimated at 15 km/h (Snow, 1964).

Because the Rio Mantaro valley was sparsely populated in this stretch, damage due to flooding was not great. However, 13 bridges, three of them in the valley inundated by the impoundment, were reported destroyed. Cultivated lands on eroded terraces were damaged. The greatest changes caused by this catastrophic rockslide, and resulting debris flow and/or flood, were to the morphology of the river valley. Following failure of the landslide dam, the channel level was rapidly elevated for several kilometers downstream due to deposition of the coarse materials from the dam. The river was perched on a sediment sheet that thinned downstream from the site.

As of 1965, a break in slope still existed at the landslide dam site, preserved by large residual boulders. In addition, as the river cut down through the residual material from the dam, new terraces were formed. Snow (1964) noted that construction of hydroelectric structures had been proposed for this stretch of the Rio Mantaro, and that the possibility of future changes in the stream regimen should be considered in the siting and design of such structures.

Nevados Huascaran debris avalanche, 1962

On January 10, 1962, a large debris avalanche was caused by the catastrophic failure of the west front of the hanging glacier on the north peak of Nevados Huascaran in the Cordillera Bianca of Peru (Fig. 1) at an elevation of 6300 m (McDowell and Fletcher, 1962; Morales, 1966; Cluff, 1971). The original ice avalanche became a high-velocity debris avalanche as it gathered a great volume of blocks of granodiorite and descended 4000 m down the steep slopes of the highest peak in the Peruvian Andes, destroying everything in its path. Morales (1966) estimated that the maximum velocity of the avalanche was ~100 km/h and that the average velocity was 60 km/h. However, McDowell and Fletcher (1962) stated that the elapsed time from inception of the avalanche to arrival at the village of Ranrahirca was 5 min, requiring an average velocity of ~170 km/h. Nine small towns (including part of Ranrahirca) were destroyed and ~4000–5000 people were killed. Cultivated fields were devastated, thousands of farm animals were killed, and great destruction occurred in an area famous for its beauty and fertility.

Morales (1966) estimated that a total volume of ~13 × 106 m3 of rock, soil, and ice was deposited by the avalanche. Of this total, ~20%–25% consisted of ice. Of the remainder, two-thirds was composed of sand and fine constituents and the remaining one-third was gravel and boulders. Some of the large granodiorite blocks carried to the toe of the avalanche weighed more than 6000 t; the largest measured had dimensions of 20 × 15 × 12 m (Dollfus and Penaherrera, 1962).

Nevados Huascaran debris avalanche, 1970

The greatest number and most destructive landslides in the Andes known to have been triggered by a single event of any kind were those associated with the M = 7.75 earthquake of May 31, 1970, the epicenter of which was off the coast of Peru (Cluff, 1971; Plafker et al., 1971; Plafker and Ericksen, 1978). Not only did this earthquake devastate the city of Huaraz, but it caused many thousands, or perhaps tens of thousands, of landslides within a 30 000 km2 area. The farthest landslide activity was ~200 km from the epicenter (Plafker et al., 1971; Keefer, 1984).

By far the most catastrophic of the landslides triggered by the 1970 earthquake originated from the north peak of the Nevados Huascaran (Fig. 1), the source of the 1962 debris avalanche. This cataclysmic debris avalanche (Fig. 22) involved 50–100 × 106 m3 of rock, snow, and ice. The mass traveled 14.5 km, falling nearly 4000 m from its source at an elevation of ~6000 m to the city of Yungay (Fig. 1) at an average velocity of between 280 and 335 km/h (Plafker et al., 1971). The debris avalanche devastated ~22.5 km2 of the mountain slope between the avalanche source and Yungay. Many farms and small settlements were obliterated, but the greatest damage and loss of life was in a densely populated area of relatively low relief below ~2600 m elevation. Here, the city of Yungay (estimated pre-landslide population of 18 830) and part of the smaller town of Ranrahirca (population 1850) were buried by the avalanche; more than 18 000 people were killed in the two towns.

Figure 22.

1970 earthquake-induced debris avalanche on Nevado Huascaran, Peru. Town of Yungay is buried beneath landslide in middle foreground. Avalanche descended ~3500 m in traveling ~14 km from its source to Rio Santa (Plafker et al., 1971). (Photo courtesy of Servicio Aerofotografico Nacional de Peru; June 13, 1970.)

Figure 22.

1970 earthquake-induced debris avalanche on Nevado Huascaran, Peru. Town of Yungay is buried beneath landslide in middle foreground. Avalanche descended ~3500 m in traveling ~14 km from its source to Rio Santa (Plafker et al., 1971). (Photo courtesy of Servicio Aerofotografico Nacional de Peru; June 13, 1970.)

Within a few minutes after the earthquake, the avalanche had sped 14 km from the north peak of Huascaran to the valley of the Rio Santa below Yungay (Plafker et al., 1971). The debris dammed the Rio Santa, temporarily causing it to back up for a distance of 1 km. The natural dam was soon overwhelmed, and a large destructive flow of debris and muddy water passed on down the Rio Santa to the sea, causing extensive damage to structures, transportation routes, and communication systems downstream from Yungay. The average velocity of this debris flow and/or flood as it raced to the sea was ~35 km/h.

Chungar rock avalanche and resulting displacement wave, 1971

On March 18, 1971, a catastrophic water wave generated by a rock avalanche struck the camp of the Chungar Mining Company along the shore of Lago Yanahuin in the Peruvian Andes (Fig. 1), killing an estimated 400–600 people and demolishing all but a few of the surface facilities of the mine (Plafker and Eyzaguirre, 1979). Chungar, the site of the Chungar Mining Company property, is located in the Province and Department of Pasco, Peru, ~65 km southwest of Cerro de Pasco and 80 km northwest of La Oroya. The camp was constructed on the north shore of Lago Yanahuin, a small moraine-dammed lake at an elevation of ~4400 m near the divide between the Pacific and Atlantic drainages.

The rock avalanche fell from an outcrop of closely jointed limestone situated ~400 m above the lake (Plafker and Eyzaguirre, 1979). The avalanche debris, with an estimated volume of 100 000 m3, consisted mainly of blocks of limestone, some of which weighed as much as 90 t. Water displaced by the avalanche formed a wave that washed the opposite shore of Lago Yanahuin to a height of 30 m, devastating almost all of the mining camp except for two concrete block bunkhouses. In addition, water poured into a mine shaft and drowned several miners.

Information on the cause of the avalanche and its mechanism is too sparse to permit any firm conclusions. Early reports that the avalanche was earthquake induced were erroneous (Plafker and Eyzaguirre, 1979). Failure of the slope was probably the result of gradual oversteepening due to headward erosion.

Mayunmarca landslide and debris flow, 1974

On April 25, 1974, a massive rockslide–debris flow (Fig. 23) dammed the Rio Mantaro in the Andes of central Peru (Fig. 1), about halfway between the cities of Huancayo and Ayacucho (Hutchinson and Kojan, 1975; Lee and Duncan, 1975; Kojan and Hutchinson, 1978). The rockslide originated at the head of a tributary valley (Quebrada Ccochacay) of the Rio Mantaro that was occupied by several small villages, the principal one being Mayunmarca. The total estimated volume of the landslide varied from 1 × 109 m3 (Kojan and Hutchinson, 1978) to 1.6 × 109 m3 (Lee and Duncan, 1975). Lee and Duncan (1975) estimated that the volume of the landslide dam (the lower part of the slide) was 1.3 × 109m3.

Figure 23.

Oblique aerial photograph of 1974 Mayunmarca, Peru, landslide, looking west from left bank of Rio Mantaro (June 4, 1974, photo by Eugene Kojan: Hutchinson and Kojan. 1975).

Figure 23.

Oblique aerial photograph of 1974 Mayunmarca, Peru, landslide, looking west from left bank of Rio Mantaro (June 4, 1974, photo by Eugene Kojan: Hutchinson and Kojan. 1975).

The landslide originated as a rockslide in beds of the Permian Mitu Formation, locally consisting of a well-bedded arkosic sandstone. The rockslide descended rapidly down Quebrada Ccochacay toward the Mantaro. Estimates of the average velocity of the slide were generally between 120 and 140 km/h (Kojan and Hutchinson, 1978). In its lower reaches, the slide was transformed into the massive debris flow that dammed the river. The total length of the landslide during its drop from a source elevation of ~4200 m to river elevation of ~2400 m was 8 km.

There was no obvious triggering event for this landslide. such as an earthquake, an intense rain storm, or abnormally high seasonal rainfall (Kojan and Hutchinson, 1978). The fundamental cause of the rockslide-debris flow apparently was the long-term downcutting of the Mantaro River, and, particularly, of its tributary, Quebrada Ccochacay.

The landslide dam resulting from the Mayunmarca landslide had a height of ~150 m. The total volume of water impounded in the 30-km-long lake was estimated at 670 × 106 m3. The filling of the lake reportedly caused numerous landslides along the shore. On June 6, 1974, 43 days after the landslide, overtopping and breaching of the dam occurred. A deep gorge was rapidly eroded through the dam, leading to rapid drawdown of the lake. Peak discharge has been estimated at from 7000 to 15 000 m3/s (Kojan and Hutchinson, 1978). The maximum rate of drawdown of the impounded lake, reached between June 8 and 9, was ~40 m/day. As a result of this drawdown, slides occurred around the periphery of the lake.

The downstream flood was a debris flow that deposited large volumes of sand and gravel for many kilometers. The flood wave had an estimated height of 20 m at the Mantaro Power Station, 100 km downstream (Kojan and Hutchinson, 1978). Estimates of the initial velocity of the flood wave varied from 15 to 30 km/h. An unconfirmed report on June 11 indicated that the flood wave had by then traveled 800 km downstream, at an average speed of 11 km/h for that period (Kojan and Hutchinson, 1978). Erosion that accompanied the flood led to many additional landslides on the banks of the Mantaro.

The number of people dead and missing due to the landslide was reported as 317 and 134, respectively (Kojan and Hutchinson, 1978; Carrillo-Gil and Carrillo-Delgado, 1988). Most of these were inhabitants of the town of Mayunmarca and other villages, which were destroyed or badly damaged by the rockslide. Because of adequate warnings, apparently none were killed by the debris flood resulting from failure of the landslide dam. However, the flood caused extensive damage: ~20 km of the main road from Huancayo to Ayacucho were destroyed directly by the flood or by related landslides, and three bridges were demolished. About 1000 people had to be evacuated from their homes during the flood, and many whose farms were destroyed had to leave their homes permanently. Upstream from the landslide dam, an additional 29 km of the Huancayo-Ayacucho highway on the left bank of the Rio Mantaro were destroyed by landslides caused by filling and rapid drawdown of the lake. This highway has not been rebuilt.

Chile

Rinihue landslides, 1960

On May 22, 1960, one of the world's strongest historic earthquakes (MW = 9.5) (Kanamori, 1977) struck the coast of south-central Chile, causing numerous major landslides and hundreds of surficial slides (Figs. 1 and 24; Davis and Karzulovic, 1961, 1963; Weischet, 1963; Ericksen et al., 1989). Locally, 75% of the timber cover was stripped by landsliding. The largest individual mass movements triggered by this earthquake were three contiguous landslides, with a total volume of ~40 × 106 m3, that dammed the Rio San Pedro near the outlet of Lago Rinihue (Fig. 24), a large moraine-dammed lake 65 km east of the city of Valdivia (Davis and Karzulovic, 1963). The largest of these three landslides (30 × 106 m3) began in an 80-m-thick sequence of Pleistocene lacustrine clays underlain by glacial till and overlain by glacial outwash (Weischet, 1963). That this landslide traveled 500 m horizontally with a vertical drop of only 50 m is indicative of the character of failure in the Pleistocene lake clays, which practically liquefied to become a porridge-like flowing mass.

Figure 24.

Map of Rio San Pedro and Lago Rinihue area in 1961 showing locations of ancient landslides and earthquake-induced landslides of May 22, 1960 (after Davis and Karzulovic, 1963).

Figure 24.

Map of Rio San Pedro and Lago Rinihue area in 1961 showing locations of ancient landslides and earthquake-induced landslides of May 22, 1960 (after Davis and Karzulovic, 1963).

The lake created by the landslide rose 26.5 m before overtopping. The amount of water impounded is questionable; however, Davis and Karzulovic (1961) estimated the volume of impoundment at 2.5 × 109 m3. While the lake was rising, spillway channels were dug across the crest of the dam in an attempt to control the rate of discharge upon overtopping. These channels slowed erosion of the dam; however, the broad valley downstream, just east of Valdivia, was flooded to depths of 5–6 m. This flood carried away many buildings, washed away railroad grades and roads, and covered areas in the valley with sand and gravel. Because of adequate warning, there were no injuries.

Other large prehistoric and historic landslides had previously blocked the outlet of Lago Rinihue. For example, an earthquake-triggered landslide (estimated volume: 100 × 106 m3) blocked the outlet of the lake in December 1575 (Davis and Karzulovic, 1961). After nearly 4 months, this landslide dam failed causing a catastrophic flood that destroyed a large part of Valdivia. Thus, the events of 1575–1576 appear to have been duplicated nearly 400 yr later; fortunately, the 1960 flood was not so disastrous.

El Alfalfal (Rio Colorado) rockslide and/or avalanche and debris flow, 1987

On November 29, 1987, a catastrophic debris flow on the Rio Colorado in Chile (Figs. 1 and 25) destroyed the campsite, access roads, bridges, and equipment that were supporting construction of the El Alfalfal 160 MW hydroelectric power plant, causing 29 deaths and considerable damage not only to El Alfalfal, but to the preexisting 25 MW Maitenes hydroelectric power plant (Fig. 26) (Valenzuela and Varela, 1991; Casassa and Marangunic, 1993; Hauser, 1993, and this volume). The economic impact was estimated at more than $65 million (U.S.). This landslide resulted in considerable public alarm in Chile because it affected an area only a few kilometers from Santiago, the capital city.

Figure 25.

Map of area affected by November 1987 El Alfalfal (Rio Colorado) rockslide and ensuing debris flow, Chile (after Casassa and Marangunic, 1993; Hauser, 1993).

Figure 25.

Map of area affected by November 1987 El Alfalfal (Rio Colorado) rockslide and ensuing debris flow, Chile (after Casassa and Marangunic, 1993; Hauser, 1993).

Figure 26.

Maitenes Power House (Fig. 25) on Rio Colorado, Chile, partially buried by debris and mud from El Alfalfa] (Rio Colorado) debris flow of November 1987.

Figure 26.

Maitenes Power House (Fig. 25) on Rio Colorado, Chile, partially buried by debris and mud from El Alfalfa] (Rio Colorado) debris flow of November 1987.

The debris flow originated as a massive rockslide or rockfall and/or avalanche in sedimentary rocks at an elevation of 4700 m on the headwaters of the Estero Parraguirre (Parraguirre Creek), a tributary of the Rio Colorado (Valenzuela and Varela, 1991). The volume of rock involved in the initial landslide has been estimated at between 2.5 × 106 and 5.5 × 106 m3. The ensuing debris flow traveled ~50 km down the Estero Parraguirre and the Rio Colorado to within 50 km of Santiago (Fig. 25).

The sedimentary rocks involved in the original rockfall and/or avalanche were steeply dipping limestones, shales, and calcareous sandstones of the Lo Valdes Formation and conglomerates, sandstones, and siltstones of the Rio Damasa Formation; these rocks form the high mountains along the border with Argentina in this area. The nearly vertical dip and open subvertical fractures have resulted in unstable large-dimension rock blocks. The strength of the rock may have been further reduced by hydrothermal alteration, which is evident at the site. Triggering of the initial failure appeared to have been caused by significant water infiltration through the fracture system due to extreme snow melt.

The catastrophic, high-velocity slope failure probably combined fall, toppling, and avalanching of unstable large-dimension blocks and sliding of others. The rock mass suddenly fell from a maximum elevation of 4700 m to ~3500 m at the toe of the slope. Because of the large mass involved and the considerable height of fall, the energy generated was significant. The Institute of Seismology of the University of Chile noted that a M = 3 earthquake was registered at precisely the time of impact of the rockfall (Eisenberg and Pardo, 1988).

The kinetic energy of the rock mass at the toe of the slope led to an estimated velocity of 100 km/h at the head of the debris flow in the Estero Parraguirre. According to witnesses, the flow occurred as an enormous wave, which often reached a height as great as 20 m (Valenzuela and Varela. 1991). Impressive evidence of the power of this wave and the debris flow was a boulder (Fig. 27), more than 10 m in diameter, that was transported ~14 km along the bed of the Rio Colorado (Fig. 27).

Figure 27.

10-m-diameter boulder from November 1987 El Alfafal debris flow in valley of Rio Colorado, Chile. Boulder was dragged ~14 km by debris flow (photo by A. Hauser, Servicio Nacional de Geologia y Mineria, Chile; Hauser, 1993).

Figure 27.

10-m-diameter boulder from November 1987 El Alfafal debris flow in valley of Rio Colorado, Chile. Boulder was dragged ~14 km by debris flow (photo by A. Hauser, Servicio Nacional de Geologia y Mineria, Chile; Hauser, 1993).

The El Alfalfal hydroelectric power plant was finally completed in 1990, after a one-year delay caused by the debris flow and after modification of the design of the water intakes to minimize the possibility of damage due to future debris flows. The Maitenes power plant (Fig. 26) returned to operation in 1992. A rock embankment was built around the power house in order to protect it from future debris flows.

Antofagasta debris flow, 1991

On June 18, 1991, after unusually heavy rain, Antofagasta, a coastal city of Chile (Fig. 1) 1300 km north of Santiago, was hit by several debris flows. The flows and associated flash floods killed 101 people and resulted in another 48 missing (Van Sint Jan, 1994). They destroyed 402 houses and damaged more than 2000. In addition, Antofagasta's water-supply system, roads, and railway lines were damaged, affecting a total of 21 000 people. Total losses were estimated at $27 million (U.S.).

The debris flows came from a dozen normally dry ravines that drain the western edge of the Cordillera de la Costa (Van Sint Jan and Talloni, 1993). The ravines cut through Antofagasta before reaching the Pacific Ocean. The estimated velocity of the flows along the Quebrada El Jardin (Jardin Creek) was 30 km/h. Erosion caused by the flows affected streets, culverts, and construction along the courses of the ravines. At the same time, debris transported by the flows destroyed many houses. The total mass of detrital material in the flows was estimated at 500000–700000 m3.

These debris flows were triggered by precipitation that ranged from 14 to 60 mm in 3 h (Van Sint Jan and Talloni, 1993). Historical records indicate that this was the equivalent of a 100 yr storm. These records also indicate the occurrence of similar flows at least five times since 1940 in this area; however, none of these previous flows caused as much damage to Antofagasta because the city was smaller at that time.

It will be difficult to prevent similar damage in future occurrences of debris flows in Antofagasta and other coastal cities in northern Chile because of their particularly susceptible locations and the practice of constructing low-income housing in ravines in the narrow strip of land between the western edge of the Cordillera de la Costa and the Pacific Ocean. At present, a series of studies is under way to determine proper designs for diversion and retaining structures intended to minimize the effects of future debris flows in Antofagasta and nearby cities. These studies are being complemented by more appropriate land planning and zoning than have been used in the past.

Argentina

Debris flow on the Rio Barrancas and Rio Colorado, 1914

The Rio Barrancas, which heads in the high Andes at the Chilean border and forms the boundary between the northwestern Argentine Provinces of Neuquen and Mendoza, was dammed in prehistoric time by a large landslide, impounding 21.5-km-long Lago Cari Lauquen in the high Andes (Figs. 1 and 28). The lake is ~400 km south-southeast of the city of Mendoza and 325 km northwest of the city of Neuquen. About 60 km downstream from the lake, the Rio Barrancas joins the Rio Grande to form the Rio Colorado, which flows a distance of ~1000 km before entering the Atlantic Ocean.

Figure 28.

Map of Rio Barrancas and Rio Colorado area of central Argentina showing location of prehistorically impounded Lago Cari Lauquen and of path of 1914 debris flow that resulted from failure of natural dam.

Figure 28.

Map of Rio Barrancas and Rio Colorado area of central Argentina showing location of prehistorically impounded Lago Cari Lauquen and of path of 1914 debris flow that resulted from failure of natural dam.

In 1914, the Rio Barrancas breached its high landslide dam; overnight, the original Lago Cari Lauquen was reduced to a “permanent” length of 5.6 km and its surface was lowered ~95 m (Fig. 29). The dam failure resulted in a catastrophic flood of water, rock, and soil, which today would be classified as a debris flow. This flow, with an estimated volume of 2 × 109 m3, devastated the downstream valleys of the Rio Barrancas and the Rio Colorado (Groeber, 1916). (Groeber called the result of the dam break a “flood,” but his description clearly indicates that it was mainly a debris flow.)

Figure 29.

Sketch of Lago Cari Lauquen on Rio Barrancas (Fig. 28), Argentina, and source of prehistoric landslide that dammed river. Sketch shows status of lake after partial failure of natural dam in 1914. Location of outlet of lake is shown by S at left edge (sketch by P. Groeber [1916, Plate VI]).

Figure 29.

Sketch of Lago Cari Lauquen on Rio Barrancas (Fig. 28), Argentina, and source of prehistoric landslide that dammed river. Sketch shows status of lake after partial failure of natural dam in 1914. Location of outlet of lake is shown by S at left edge (sketch by P. Groeber [1916, Plate VI]).

No data are readily available on casualties or damage costs from the disaster. The area was not heavily populated. However, Groeber (1916) reported that cattle ranches and farms along the 60 km canyon and valley of the Rio Barrancas upstream from its junction with the Rio Grande completely disappeared; fields of wheat, corn, and alfalfa were buried by debris. In addition, two commissariats (small towns) in the valley of the Rio Barrancas were devastated. The debris flow and flood continued in the Rio Colorado well into La Pampa and Rio Negro Provinces, more than 300 km downstream from the remnant of Lago Cari Neuquen. As was the case in the valley of the Rio Barrancas, farms and ranches on both sides of the valley of the Rio Colorado were wiped out, as were roads along the Rio Colorado. Groeber (1933) noted that, 20 years later, farmland in the valleys of the Rio Barrancas and Rio Colorado had not recovered from the devastation.

One compensation resulting from failure of the landslide dam and subsequent lowering of the lake surface was that ~16 km2 of the bottom of the old lake were uncovered to form a ground surface of sandy and/or clayey soil suitable for farming development (Groeber, 1916).

Rio Escoipe debris flow, Salta Province, 1976

Although there is abundant geologic evidence of prehistoric landslides on the eastern slopes of the Andes of Argentina (Fauque and Tchilinguiarian, this volume), information on historic catastrophic landslides in Argentina has not been widely circulated. Notable exceptions have been damaging debris flows that have occurred regularly in Jujuy and Salta Provinces in extreme northern Argentina (Marcuzzi et al., 1994; Chayle and Wayne, 1995). Probably the best known of these events is the debris flow of January 17, 1976, that swept down the Rio Escoipe in Salta Province and buried the prosperous town of San Fernando de Escoipe under 3 m of mud and rock (Igarzabal, 1979; Wayne, 1987) (Fig. 1). The town was almost totally destroyed; only a few houses situated on elevated slopes at the edge of the town were spared. The debris flow, which originated in submetamorphic rocks through which the Rio Escoipe flowed, was caused by record rainfall during the summer of 1975–1976. A nearby meteorological station registered 207 mm of rain during January, compared to an average January rainfall of 68.7 mm recorded for the period from 1973 to 1985 (Wayne, 1987).

Storms such as the one that destroyed San Fernando de Escoipe in 1976 seem to have coincided with years affected by the El Niño–Southern Oscillation phenomenon (Alonso and Wayne, 1992). Nearly all of the precipitation in northern Argentina occurs in the period from January to March, and major debris flows occur when storms drop a large amount of rainfall in a few hours on saturated slopes. Debris flows similar to the Rio Escoipe event destroyed housing and disrupted roads and railroads along the Rio Grande in Jujuy Province at the villages of Purmamarca (January 1984) and Humahuaca (January 1986 and March 1990) (Wayne and Alonso, 1991).

Brazil

In its summer season of December to March, mid-southern Brazil, with its south-facing coast and rugged coastal mountains, is particularly susceptible to cloudbursts, which result in floods, erosion, and landslides. The coastal mountains are formed primarily of granite gneiss and migmatite, covered with thick deposits of residual and colluvial soils. The combination of steep slopes, heavy rainfall, residual soils, and weathered rocks has made these coastal mountains particularly susceptible to recurring major, catastrophic landslide activity. Urban growth in Rio de Janeiro and nearby cities, in which development has spread from the lowlands onto the slopes, and the attendant construction of highways requiring huge side-hill cuts and fills have caused many slope-stability problems (Da Costa Nunes et al., 1979). The types of landslides that occur under these conditions include rockfalls, rock and debris slides, block glides, debris avalanches, and debris flows and mudflows. Most start as thin slides in saturated residual soils, and are rapidly transformed into fast-moving debris avalanches, and then into debris flows and mudflows. Many such landslide events have occurred in this area historically. Nieto and Barany (1988) noted that major rainfall-caused landslide events were recorded in the Rio de Janeiro area (including the Serra das Araras) as early as 1916. Because of space limitations, we review only the three largest, most catastrophic, and best-reported events: the 1966 and 1967 landslide disasters in Rio de Janeiro Province and the 1988 major landslides in the vicinity of Rio de Janeiro and Petropolis (Fig. 1).

Landslides in Rio de Janeiro and the Serra das Araras, 1966 and 1967

Unusually heavy rains fell in mid-southern Brazil during the summers of 1966 and 1967 (Barata, 1969; Da Costa Nunes, 1969; Jones, 1973). In 1966, the area most affected was the city of Rio de Janeiro and vicinity. Total loss of life from floods and landslides in the area may have reached 1000. In 1967, the area most affected was 100 km2 along the escarpment of the Serra das Araras (Fig. 30), 50–70 km west of Rio de Janeiro; deaths from floods and landslides were estimated to be as high as 1700. Property and industrial damage was described by Jones (1973) as “inestimable.” The slides, avalanches, and flows resulted in immense human and material losses in the Serra das Araras mountain region along the most important highway in Brazil, the heavily traveled Rio de Janeiro–Sao Paolo highway, which had not suffered any previous landslide damage in its 39 years of existence (Da Costa Nunes, 1969; Da Costa Nunes et al., 1979). In addition, much damage was done to important hydroelectric installations in the area. Hillsides were devastated by thousands of thin debris slides and avalanches (Figs. 31 and 32).

Figure 30.

Map of Serra das Araras, Brazil, landslide disaster area showing zone (inside dashed line) of destruction after rainstorm of January 22 and 23, 1967 (after Jones, 1973).

Figure 30.

Map of Serra das Araras, Brazil, landslide disaster area showing zone (inside dashed line) of destruction after rainstorm of January 22 and 23, 1967 (after Jones, 1973).

Figure 31.

Typical debris avalanche in thin residual soil that occurred in 1967 in Serra das Araras. Brazil (photo by F.O. Jones. U.S. Geological Survey; Jones, 1973).

Figure 31.

Typical debris avalanche in thin residual soil that occurred in 1967 in Serra das Araras. Brazil (photo by F.O. Jones. U.S. Geological Survey; Jones, 1973).

Figure 32.

Landslide failure of new highway in Sena das Araras, Brazil, caused by storm of January 22–23, 1967. Prior to disaster, valley bottom contained village and highway construction camp: these were destroyed by mud-flow in valley that killed several hundred people. Mudflow was ~4 m deep at this location (photo by F.O. Jones, U.S. Geological Survey; Jones, 1973).

Figure 32.

Landslide failure of new highway in Sena das Araras, Brazil, caused by storm of January 22–23, 1967. Prior to disaster, valley bottom contained village and highway construction camp: these were destroyed by mud-flow in valley that killed several hundred people. Mudflow was ~4 m deep at this location (photo by F.O. Jones, U.S. Geological Survey; Jones, 1973).

Jones (1973, p. 1) expressed the intensity and enormity of the 1967 event as follows:

On the night of January 22 and 23, 1967, a landslide disaster of unbelievable magnitude struck the Serra das Araras region of Brazil. Beginning at about 11:00 p.m., an electrical storm and cloudburst of 3½ hours duration laid waste by landslides and fierce erosion a greater land mass than any ever recorded in geological literature. The area laid waste was 25 kilometers in length and 7 to 8 kilometers in maximum width. A large part of the area of heavy destruction was on the steep slopes of the Serra das Araras escarpment. Thunderbolts from lightning and the collapse of the hills shook the region like an earthquake. Landslides numbering in the tens of thousands turned the green vegetation-covered hills into wastelands and the valleys into seas of mud.

In terms of casualties, one of the worst individual events occurred in the Bairro Jardim-Laranjeiras of Rio de Janeiro on February 18, 1967 (Da Costa Nunes et al., 1979). A high-velocity landslide occurred in a mass of residual soil and altered granite following very heavy rainfall. The slide was aggravated by the removal of substantial material from the toe of the potential slide area for use in clandestine fills. The saturated soil failed and formed a high-velocity debris avalanche that destroyed three buildings (Fig. 33), two of which were apartment houses. In only a few seconds, 110 people were killed in the most tragic individual accident of its kind in Brazil.

Figure 33.

February 18, 1967. Bairro Jardim-Laranjeiras landslide. Rio de Janeiro; landslide resulted in destruction of two apartment buildings and death of 110 people (Da Costa Nunes et al., 1979). (March 20, 1967, photo by Ruy Macial, Geo-Rio, Rio de Janeiro.)

Figure 33.

February 18, 1967. Bairro Jardim-Laranjeiras landslide. Rio de Janeiro; landslide resulted in destruction of two apartment buildings and death of 110 people (Da Costa Nunes et al., 1979). (March 20, 1967, photo by Ruy Macial, Geo-Rio, Rio de Janeiro.)

Jones (1973, p. 5, 6) summarized the incredible rainfall statistics leading up to these 1966 and 1967 landslide disasters:

During the 1966 season, two exceptionally heavy rains fell; they were the storms of January 10, 11, and 12, and March 26 and 27. On January 10, 1966, a cold front moved into the city of Rio de Janeiro area and remained stationery there for 3 days. At the meteorological observatory in the center of Rio, the oldest station in the city, which has about 80 years of recorded observation, the depth of rainfall in the 3 days reached a total of 484 mm (19.05 in.). The normal rainfall for January is 171 mm (6.73 in.), and the previous maximum rainfall recorded for any one month was 473 mm (18.62 in.) in January 1962. During the 3-day January 1966 storm, the Alta do Boa Vista station recorded 675 mm (27.57 in.) of precipitation.

The storm of March 26 and 27 began about 3 p.m. Precipitation was most intense during the early part of the storm when 240 mm (8.45 in.) of rain fell in 6 hours. The intensity reached 100 mm (3.94 in) per hour. During the 18 hours of total duration, there was 320 mm (12.6 in.) of precipitation.

The storm that caused the 1967 catastrophic landslides began ~11:00 p.m. on the night of January 22 and continued into January 23. Jones (1973, p. 22) presented the following rainfall data for this short-lived storm:

In the area of the generating complex, there were three rain gages. During the storm, the rainfall recorded at these gages was as follows: Fazenda da Rosa, 275 mm (10.83 in.); Ipe Acampamento, 225 mm (8.85 in.); and the Lajes Creek dam, 218 mm (8.58 in.). Between 30 and 50 minutes after the beginning of the storm the Lajes Creek dam station recorded intensities varying from 100 to 114 mm per hour.

Landslides in Rio de Janeiro and Petropolis, 1988

Heavy and persistent rains that fell along the mountainous mid-southern coast of Brazil in February 1988 caused thousands of landslides of the same type as occurred in nearly the same region in 1966 and 1967. The cities of Rio de Janeiro and Petropolis (Fig. 1) were particularly hard hit, with a total landslide death toll of ~320 (Nieto and Barany, 1988; Ogura and Filho, 1991). Perhaps as much as 80% of the landslides in these cities was related to human activities, mainly cuts and fills for highways and other construction. However, the two largest, most violent, and most destructive single landslides were natural, occurring in saturated residual and colluvial soils; they began as rockslides and/or avalanches that became debris flows as they moved downslope.

Nieto and Barany (1988) summarized the sequence of February rainfall and landslide events in Petropolis and Rio de Janeiro as follows.

Petropolis

On February 1, unusually heavy rainfall resulted in flooding of the three principal rivers in the Petropolis region: Rio Quitandinha, Rio Paibanha, and Rio Palatinato. Some small landslides occurred.

On February 2, a second series of floods occurred during the night, resulting in further isolated landslides. At this time, there were no recorded fatalities as a result of the minor landsliding in some sections of the city.

On February 5–6, Petropolis was hit by intense rains, resulting in two flooding events. Immediately following each of the cloudbursts, a large number of landslides occurred throughout Petropolis. The largest and most damaging landslides (and floods) occurred during the night, resulting in the greatest number of casualties. At this time in Petropolis, 171 had been killed, 600 injured, and 4263 left homeless.

Rio de Janeiro

Rio de Janeiro was hit by its heaviest rainfall about a week after the disastrous events in Petropolis.

On February 19, heavy rains in the preceding week culminated in violent flooding throughout the city and catastrophic landslides in the inhabited hills surrounding the city; ~120 residents of Rio de Janeiro were killed and 22 000 made homeless by the landslides and floods. One of the most disastrous landslides destroyed the Santa Genoveva Hospital, a geriatric facility in the suburb of Santa Teresa, resulting in 34 deaths. The flow event occurred barely 1 h after the very intense evening rains had begun.

On February 20, very heavy rains and landslides continued in the northern part of metropolitan Rio de Janeiro.

The rocks underlying the cities of Rio de Janeiro and Petropolis consist of a wide variety of granites, gneisses, migmatites, schists, and other metamorphic and intrusive varieties (Nieto and Barany, 1988). The steep (>35°) slopes of the picturesque promontories that provide the tourist appeal for Rio de Janeiro and Petropolis are either bare or covered by a thin veneer of weathered rock and residual soil, which are highly susceptible to thin, surficial slides. The 1988 flooding and landslide events were triggered by the heavy rains of early and mid February. For example, the weather station of Campo Grande, ~36 km west of downtown Rio de Janeiro, recorded 230 mm of precipitation on February 2. In downtown Petropolis, the total precipitation for the period February 1–24 was 776 mm (Nieto and Barany, 1988).

Brazilian engineering geologists have been studying the correlation between rainfall and landslide occurrence since the mid-1950s, beginning with the work of Vargas and Pichler (1957). All such studies have emphasized that, for major landslide activity to occur, antecedent rainfall is required in addition to the heavy rainfall from the landslide-triggering storm (Nieto and Barany, 1988). Guidicini and Iwasa (1977) showed that catastrophic landslide events in the region occur at the end of rainy seasons in which the cumulative precipitation is higher than the mean precipitation for such seasons. Tatizana et al. (1987) noted a strong correlation between landslide activity and four-day cumulative precipitation for the area, and Imamoto et al. (1989) concluded in reference to the 1988 landslides that “rainfall characteristics of this disaster is not the concentration of heavy rain in a short time but the intermittent continuation of less heavy rain for a long time.”

Summary and Conclusions

In South America, conditions that lead to catastrophic mass movements occur most commonly in the Andes Mountains and in the Brazilian Highlands. The processes and effects involved in the 23 local and regional events discussed herein are summarized in Table 1. The processes that most probably triggered these landslide events are noted in Table 2. The types of landslides involved in these disasters ranged from high-velocity rockslides and rock or debris avalanches to high- to medium-velocity debris flows and mudflows. Often, individual events consisted of combinations of two or more of these landslide types acting in sequence. Most casualties were caused by high-velocity avalanches and high- to medium-velocity, highly mobile, long-runout debris flows. A common, and particularly devastating, occurrence was an earthquake-triggered slide of previously saturated residual soil that was rapidly transformed on a steep slope into a very fluid, high-velocity debris avalanche, which in turn changed into a devastating mobile debris flow upon reaching the flatter valley bottom. Also common were similar events triggered by heavy rainfall. The outstanding exception to the many earthquake- and rainfall-triggered events was the volcanologically triggered 1985 Nevado del Ruiz debris-flow disaster in Colombia, in which more than 22000 people were killed; this event was one of the world's outstanding landslide disasters of the twentieth century.

Table 1.

Summary of Catastrophic Landslides in South America, by Country

Country and yearName of landslideTriggering processType of landslideEstimated volume or areaSocioeconomic and/or topographic effectsReferences
Venezuela
1987Rio LimonHeavy rainDebris flows2 × 106m3210 killed, 400 injured, 30,000 homeless.Elizalde et al. (1987); Salcedo and Vignoli (1987); Montes (1989)
1993 and other yearsCaracasHeavy rainSlides and flowsDamaging events several times. Event in 1993: no casualties, but several expensive homes and local street destroyed.Singer (1983); Salcedo (1984)
Colombia
1985Nevado del RuizVolcanic activityDebris flows (lahars)More than 22,000 killed; 3400 ha of farmland buried; destroyed or damaged 2 hospitals, 58 industries, 343 businesses.Herd (1986); Garcia (1988); Voight (1990); Miletti et al. (1991)
1987Villa TinaPond leakageSoil slide20 × 103 m3At least 217 deaths; 80 houses destroyed.Tokuhiro (1988)
1994PaezEarthquakeSlides, avalanches, debris flowsLength of major flows: 120 kmAbout 2000 killed or missing; more than 30,000 displaced; locally, more than 50% of slopes denuded.INGEOMINAS (1994); Martinez et al. (1995)
Ecuador
1983ChunchiRain and/or snow (wettest year of century)1 × 106 m3Killed more than 150; blocked PanAmerican Highway; buried vehicles.Torres (1983); Benitez (1989)
1987ReventadorEarthquakesSlides, avalanches, debris flows75–110 × 106 m3Economic losses: US$1 billion; 1000 deaths; destroyed 40 km of Trans-Ecuadorian pipeline and highway.Hakuno et al. (1988); Ishihara and Nakamura (1988); Schuster (1991); Tibaldi et al. (1995); Schuster et al. (1996)
1993La JosefinaMine excavation and heavy rainRock slide20–25 × 106 m3Slide formed 100-m-high dam of Rio Paute; failure of dam in 33 days caused 10 000 m3/s flood; hundreds of homes and industries destroyed; no casualties.Chamot (1993); Canuti et al. (1994); Ortiz et al. (1994); Plaza-Nieto and Zevallos (1994)
Peru
1941HuarazFailure of moraine dam upstreamDebris flow10 × 106 m3Destroyed 1/4 of Huaraz, killing 4000–6000 people. Debris flow dammed Rio Santa; dam failure caused flood, destroying downstream settlements and farms.Bodenlos and Ericksen (1955); Ericksen et al. (1989)
1945Cerro Condor-SenccaErosional undercuttingRock slide5.5 × 106 m3Formed 100-m-high dam of Rio Montaro, which failed after 73 days, causing flood exceeding 280 m3/s; roads, 13 bridges, and much farmland destroyed.Snow (1964)
1962Nevados HuascaranFailure of hanging glacierDebris avalanche13 × 106 m3Nine small towns destroyed; 4000–5000 people and thousands of farm animals killed.McDowell and Fletcher (1962); Morales (1966); Cluff (1971)
1970Nevados HuascaranEarthquakeDebris avalanche50–100 × 106 m3Yungay and Ranrahirca destroyed, 18 000 people killed. Failure of debris blockage of Rio Santa caused major flood.Cluff (1971); Plafker et al. (1971); Plafker and Ericksen (1978); Keefer (1981)
1971ChungarRock avalanche100 × 103 m3Water wave caused by avalanche destroyed mining camp, killing 400–600 people.Plafker & Eyzaguirre (1978)
1974MayunmarcaLong-term downcutting by Rio MontaroRock slide–debris avalanche1.0–1.6 × 109 m3As many as 317 killed. Debris avalanche dammed Rio Mantaro; dam failed in 43 days, causing major downstream damage.Hutchinson and Kojan (1975); Lee and Duncan (1975); Kojan and Hutchinson (1978)
Chile
1960RinihueEarthquakeSlides, avalanches, debris flowsLargest single slide: 30 × 106 m3Locally, 75% of timber stripped from slopes.Davis and Karzulovic (1961, 1963); Weischet (1963); Ericksen et al. (1989)
1987El Alfalfal (Rio Colorado)Rock slide, avalanche, debris flowSlide/avalanche volume: 2.5–5.5 × 106 m3Debris flow caused 27 casualties, damaged Maitenes hydroelectric plant and under-construction El Alfalfal power plant.Valenzuela and Varela (1991); Casassa and Marangunic (1993); Hauser (1993)
1991AntofagastaHeavy rainDebris flows500–700 × 103 m3Hundreds of casualties; destroyed large number of homes; heavily damaged water-supply system, roads, and railway lines.Van Sint Jan and Talloni (1993)
Argentina
1914Rio Barrancas and Rio ColoradoFailure of ancient landslide damDebris flow and floodVolume: 2 × 109 m3; length: 300 kmTwo small towns devastated; numerous ranches and farms destroyed.Groeber (1916, 1933)
1976Rio EscoipeHeavy rainDebris flowTown of San Fernando de Escoipe almost totally destroyed by 3 m of mud and rock debris.Igarzabal (1979); Wayne (1987)
Brazil
1966–1967Rio de Janeiro and Serra das ArarasHeavy rainSlides, avalanches, flowsDeaths due to landslides and floods in 1966—1000; in 1967—about 1500. Property and industrial damage “inestimable.”Barata (1969); Da Costa Nunes (1969); Jones (1973); Da Costa Nunes et al. (1979)
1988Rio de Janeiro and PetropolisHeavy rainSlides, avalanches, flowsApproximately 300 people killed; many structures destroyed.Nieto and Barany (1988); Ogura and Filho (1991)
Country and yearName of landslideTriggering processType of landslideEstimated volume or areaSocioeconomic and/or topographic effectsReferences
Venezuela
1987Rio LimonHeavy rainDebris flows2 × 106m3210 killed, 400 injured, 30,000 homeless.Elizalde et al. (1987); Salcedo and Vignoli (1987); Montes (1989)
1993 and other yearsCaracasHeavy rainSlides and flowsDamaging events several times. Event in 1993: no casualties, but several expensive homes and local street destroyed.Singer (1983); Salcedo (1984)
Colombia
1985Nevado del RuizVolcanic activityDebris flows (lahars)More than 22,000 killed; 3400 ha of farmland buried; destroyed or damaged 2 hospitals, 58 industries, 343 businesses.Herd (1986); Garcia (1988); Voight (1990); Miletti et al. (1991)
1987Villa TinaPond leakageSoil slide20 × 103 m3At least 217 deaths; 80 houses destroyed.Tokuhiro (1988)
1994PaezEarthquakeSlides, avalanches, debris flowsLength of major flows: 120 kmAbout 2000 killed or missing; more than 30,000 displaced; locally, more than 50% of slopes denuded.INGEOMINAS (1994); Martinez et al. (1995)
Ecuador
1983ChunchiRain and/or snow (wettest year of century)1 × 106 m3Killed more than 150; blocked PanAmerican Highway; buried vehicles.Torres (1983); Benitez (1989)
1987ReventadorEarthquakesSlides, avalanches, debris flows75–110 × 106 m3Economic losses: US$1 billion; 1000 deaths; destroyed 40 km of Trans-Ecuadorian pipeline and highway.Hakuno et al. (1988); Ishihara and Nakamura (1988); Schuster (1991); Tibaldi et al. (1995); Schuster et al. (1996)
1993La JosefinaMine excavation and heavy rainRock slide20–25 × 106 m3Slide formed 100-m-high dam of Rio Paute; failure of dam in 33 days caused 10 000 m3/s flood; hundreds of homes and industries destroyed; no casualties.Chamot (1993); Canuti et al. (1994); Ortiz et al. (1994); Plaza-Nieto and Zevallos (1994)
Peru
1941HuarazFailure of moraine dam upstreamDebris flow10 × 106 m3Destroyed 1/4 of Huaraz, killing 4000–6000 people. Debris flow dammed Rio Santa; dam failure caused flood, destroying downstream settlements and farms.Bodenlos and Ericksen (1955); Ericksen et al. (1989)
1945Cerro Condor-SenccaErosional undercuttingRock slide5.5 × 106 m3Formed 100-m-high dam of Rio Montaro, which failed after 73 days, causing flood exceeding 280 m3/s; roads, 13 bridges, and much farmland destroyed.Snow (1964)
1962Nevados HuascaranFailure of hanging glacierDebris avalanche13 × 106 m3Nine small towns destroyed; 4000–5000 people and thousands of farm animals killed.McDowell and Fletcher (1962); Morales (1966); Cluff (1971)
1970Nevados HuascaranEarthquakeDebris avalanche50–100 × 106 m3Yungay and Ranrahirca destroyed, 18 000 people killed. Failure of debris blockage of Rio Santa caused major flood.Cluff (1971); Plafker et al. (1971); Plafker and Ericksen (1978); Keefer (1981)
1971ChungarRock avalanche100 × 103 m3Water wave caused by avalanche destroyed mining camp, killing 400–600 people.Plafker & Eyzaguirre (1978)
1974MayunmarcaLong-term downcutting by Rio MontaroRock slide–debris avalanche1.0–1.6 × 109 m3As many as 317 killed. Debris avalanche dammed Rio Mantaro; dam failed in 43 days, causing major downstream damage.Hutchinson and Kojan (1975); Lee and Duncan (1975); Kojan and Hutchinson (1978)
Chile
1960RinihueEarthquakeSlides, avalanches, debris flowsLargest single slide: 30 × 106 m3Locally, 75% of timber stripped from slopes.Davis and Karzulovic (1961, 1963); Weischet (1963); Ericksen et al. (1989)
1987El Alfalfal (Rio Colorado)Rock slide, avalanche, debris flowSlide/avalanche volume: 2.5–5.5 × 106 m3Debris flow caused 27 casualties, damaged Maitenes hydroelectric plant and under-construction El Alfalfal power plant.Valenzuela and Varela (1991); Casassa and Marangunic (1993); Hauser (1993)
1991AntofagastaHeavy rainDebris flows500–700 × 103 m3Hundreds of casualties; destroyed large number of homes; heavily damaged water-supply system, roads, and railway lines.Van Sint Jan and Talloni (1993)
Argentina
1914Rio Barrancas and Rio ColoradoFailure of ancient landslide damDebris flow and floodVolume: 2 × 109 m3; length: 300 kmTwo small towns devastated; numerous ranches and farms destroyed.Groeber (1916, 1933)
1976Rio EscoipeHeavy rainDebris flowTown of San Fernando de Escoipe almost totally destroyed by 3 m of mud and rock debris.Igarzabal (1979); Wayne (1987)
Brazil
1966–1967Rio de Janeiro and Serra das ArarasHeavy rainSlides, avalanches, flowsDeaths due to landslides and floods in 1966—1000; in 1967—about 1500. Property and industrial damage “inestimable.”Barata (1969); Da Costa Nunes (1969); Jones (1973); Da Costa Nunes et al. (1979)
1988Rio de Janeiro and PetropolisHeavy rainSlides, avalanches, flowsApproximately 300 people killed; many structures destroyed.Nieto and Barany (1988); Ogura and Filho (1991)
Table 2.

Processes That Most Probably Triggered Catastrophic South American Landslides

Triggering processNumber of occurrences
Heavy or prolonged rainfall10
Earthquake shaking5
Valley downcutting due to long-term erosion3
Failure of natural dam2
Volcanic activity1
Ice avalanche1
Leakage from manmade pond1
Triggering processNumber of occurrences
Heavy or prolonged rainfall10
Earthquake shaking5
Valley downcutting due to long-term erosion3
Failure of natural dam2
Volcanic activity1
Ice avalanche1
Leakage from manmade pond1

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Acknowledgments

We thank Margo L. Johnson of the U.S. Geological Survey, who produced the map figures in this report by means of computer graphics, and our numerous South and North American colleagues, who provided us with ideas that led to selection of the catastrophic landslides discussed here.

Figures & Tables

Figure 1.

General physiographic map of South America showing locations (black dots) of landslide events discussed in this chapter (after Time Incorporated, 1961, p. 237).

Figure 1.

General physiographic map of South America showing locations (black dots) of landslide events discussed in this chapter (after Time Incorporated, 1961, p. 237).

Figure 2.

Average annual precipitation in South America (after Brawer, 1991).

Figure 2.

Average annual precipitation in South America (after Brawer, 1991).

Figure 3.

Zones of seismic intensity in South America. Local intensity may be even greater than indicated by legend (after Centro Regional de Sismologia para America del Sur, 1985).

Figure 3.

Zones of seismic intensity in South America. Local intensity may be even greater than indicated by legend (after Centro Regional de Sismologia para America del Sur, 1985).

Figure 4.

Landslide in area of low-cost urban housing in Caracas, Venezuela. Landslide was triggered by heavy rainfall and leakage of sewer drainage. Photo was taken in 1993.

Figure 4.

Landslide in area of low-cost urban housing in Caracas, Venezuela. Landslide was triggered by heavy rainfall and leakage of sewer drainage. Photo was taken in 1993.

Figure 5.

Homes in high-cost residential area of Caracas, Venezuela, that were destroyed on September 29, 1993, by rainfall-triggered landslide.

Figure 5.

Homes in high-cost residential area of Caracas, Venezuela, that were destroyed on September 29, 1993, by rainfall-triggered landslide.

Figure 6.

Map showing area affected by September 9, 1987, Rio Limon debris flows, Venezuela.

Figure 6.

Map showing area affected by September 9, 1987, Rio Limon debris flows, Venezuela.

Figure 7.

Vehicles destroyed by September 9, 1987, Rio Limon debris flow, Venezuela.

Figure 7.

Vehicles destroyed by September 9, 1987, Rio Limon debris flow, Venezuela.

Figure 8.

Map of Nevado del Ruiz area, Colombia, showing distribution of debris flows and/or mudflows, tephra. and volcanic ash from 1985 eruption (after Voight, 1990).

Figure 8.

Map of Nevado del Ruiz area, Colombia, showing distribution of debris flows and/or mudflows, tephra. and volcanic ash from 1985 eruption (after Voight, 1990).

Figure 9.

City of Armero. Colombia, following 1985 eruption of'Nevado del Ruiz and subsequent flooding by debris flows and/or mudflows. Most of city of 29 000 was covered by flows. (Photo by Steve Raymer, courtesy National Geographic Magazine.)

Figure 9.

City of Armero. Colombia, following 1985 eruption of'Nevado del Ruiz and subsequent flooding by debris flows and/or mudflows. Most of city of 29 000 was covered by flows. (Photo by Steve Raymer, courtesy National Geographic Magazine.)

Figure 10.

Business district in Armero, Colombia, showing effects of 1985 debris (low and/or mudflow. (Photo by R. Updike, U.S. Geological Survey.)

Figure 10.

Business district in Armero, Colombia, showing effects of 1985 debris (low and/or mudflow. (Photo by R. Updike, U.S. Geological Survey.)

Figure 11.

Large monzonite boulder on flood plain of Rio Guali, Colombia, was transported ~400 m by 1985 debris flow and/or mudflow. (Photo by R. Updike, U.S. Geological Survey.)

Figure 11.

Large monzonite boulder on flood plain of Rio Guali, Colombia, was transported ~400 m by 1985 debris flow and/or mudflow. (Photo by R. Updike, U.S. Geological Survey.)

Figure 12.

Map of Rio Paez drainage, southwestern Colombia, showing locations of Nevado del Huila volcano and epicenter (star) of 1994 earthquake. Dashed line indicates outer limits of earthquake-triggered landslides (after Martinez et al., 1995).

Figure 12.

Map of Rio Paez drainage, southwestern Colombia, showing locations of Nevado del Huila volcano and epicenter (star) of 1994 earthquake. Dashed line indicates outer limits of earthquake-triggered landslides (after Martinez et al., 1995).

Figure 13.

Slides, debris avalanches, and debris flows on valley walls of upper Rio San Vicente (Fig. 12), southwestern Colombia, triggered by 1994 Paez earthquake. (Photo taken July 1994.)

Figure 13.

Slides, debris avalanches, and debris flows on valley walls of upper Rio San Vicente (Fig. 12), southwestern Colombia, triggered by 1994 Paez earthquake. (Photo taken July 1994.)

Figure 14.

Massive debris flow entering Rio Paez near village of Irlanda (Fig. 12), southwestern Colombia. Homes and other buildings in lower right quarter of photo were destroyed by debris flow. (Photo taken July 1994.)

Figure 14.

Massive debris flow entering Rio Paez near village of Irlanda (Fig. 12), southwestern Colombia. Homes and other buildings in lower right quarter of photo were destroyed by debris flow. (Photo taken July 1994.)

Figure 15.

Home in village of Toez (Fig. 12), Rio Paez valley, southwestern Colombia, destroyed by debris flow triggered by 1994 Paez earthquake. (Photo taken July 1994.)

Figure 15.

Home in village of Toez (Fig. 12), Rio Paez valley, southwestern Colombia, destroyed by debris flow triggered by 1994 Paez earthquake. (Photo taken July 1994.)

Figure 16.

Area of mass wasting and flooding caused by 1987 Reventador earthquakes, northeastern Ecuador, indicating sections of damage to Trans-Ecuadorian oil pipeline and highway.

Figure 16.

Area of mass wasting and flooding caused by 1987 Reventador earthquakes, northeastern Ecuador, indicating sections of damage to Trans-Ecuadorian oil pipeline and highway.

Figure 17.

1987 Reventador earthquake: aerial view of northeast valley wall of Rio Malo, northeastern Ecuador, showing extreme denudation of slopes due to slips, avalanches, and/or flows and of valley bottom due to debris flows and flooding. Note vegetation trimline in main valley that indicates maximum height of debris flow and/or flood. ~25 m above current river level. (Photo taken April 1987.)

Figure 17.

1987 Reventador earthquake: aerial view of northeast valley wall of Rio Malo, northeastern Ecuador, showing extreme denudation of slopes due to slips, avalanches, and/or flows and of valley bottom due to debris flows and flooding. Note vegetation trimline in main valley that indicates maximum height of debris flow and/or flood. ~25 m above current river level. (Photo taken April 1987.)

Figure 18.

1987 Reventador earthquake: aerial view is of destruction of Trans-Ecuadorian oil pipeline and adjacent highway by earthquake-triggered debris flow issuing from minor tributary of Rio Coca. (Photo taken April 1987.)

Figure 18.

1987 Reventador earthquake: aerial view is of destruction of Trans-Ecuadorian oil pipeline and adjacent highway by earthquake-triggered debris flow issuing from minor tributary of Rio Coca. (Photo taken April 1987.)

Figure 19.

1987 Reventador earthquake: aerial view of confluence of Rio Salado (lower left) and Rio Quijos (lower right) to form Rio Coca (flowing to upper left), northeastern Ecuador (Fig. 16). Post-earthquake, braided debris-flow and flood deposits are thick as 15 m in valley bottoms. Bedrock constriction (indicated by two white arrows) probably caused shortlived damming of river, which contributed to upstream flooding and rapid sedimentation. (Photo taken April 1987.)

Figure 19.

1987 Reventador earthquake: aerial view of confluence of Rio Salado (lower left) and Rio Quijos (lower right) to form Rio Coca (flowing to upper left), northeastern Ecuador (Fig. 16). Post-earthquake, braided debris-flow and flood deposits are thick as 15 m in valley bottoms. Bedrock constriction (indicated by two white arrows) probably caused shortlived damming of river, which contributed to upstream flooding and rapid sedimentation. (Photo taken April 1987.)

Figure 20.

Map showing location of La Josefina landslide dam. temporary Lago Josefina, and path of debris flow and/or flood down Rio Paute to Amaluza Dam (after Chamot. 1993; Plaza-Nieto and Zevallos, 1994).

Figure 20.

Map showing location of La Josefina landslide dam. temporary Lago Josefina, and path of debris flow and/or flood down Rio Paute to Amaluza Dam (after Chamot. 1993; Plaza-Nieto and Zevallos, 1994).

Figure 21.

Failure of La Josefina landslide dam on April 26. 1993. Remnants of natural dam are near eenter of photo. Remnant of Lago Josefina is on Rio Paute on right in photo, and floodwaters exit in Rio Paute at lower left. Rio Jadan enters photo from left (photo courtesy of P. Chamot. United Nations Department of Human Affairs; Chamot. 1993).

Figure 21.

Failure of La Josefina landslide dam on April 26. 1993. Remnants of natural dam are near eenter of photo. Remnant of Lago Josefina is on Rio Paute on right in photo, and floodwaters exit in Rio Paute at lower left. Rio Jadan enters photo from left (photo courtesy of P. Chamot. United Nations Department of Human Affairs; Chamot. 1993).

Figure 22.

1970 earthquake-induced debris avalanche on Nevado Huascaran, Peru. Town of Yungay is buried beneath landslide in middle foreground. Avalanche descended ~3500 m in traveling ~14 km from its source to Rio Santa (Plafker et al., 1971). (Photo courtesy of Servicio Aerofotografico Nacional de Peru; June 13, 1970.)

Figure 22.

1970 earthquake-induced debris avalanche on Nevado Huascaran, Peru. Town of Yungay is buried beneath landslide in middle foreground. Avalanche descended ~3500 m in traveling ~14 km from its source to Rio Santa (Plafker et al., 1971). (Photo courtesy of Servicio Aerofotografico Nacional de Peru; June 13, 1970.)

Figure 23.

Oblique aerial photograph of 1974 Mayunmarca, Peru, landslide, looking west from left bank of Rio Mantaro (June 4, 1974, photo by Eugene Kojan: Hutchinson and Kojan. 1975).

Figure 23.

Oblique aerial photograph of 1974 Mayunmarca, Peru, landslide, looking west from left bank of Rio Mantaro (June 4, 1974, photo by Eugene Kojan: Hutchinson and Kojan. 1975).

Figure 24.

Map of Rio San Pedro and Lago Rinihue area in 1961 showing locations of ancient landslides and earthquake-induced landslides of May 22, 1960 (after Davis and Karzulovic, 1963).

Figure 24.

Map of Rio San Pedro and Lago Rinihue area in 1961 showing locations of ancient landslides and earthquake-induced landslides of May 22, 1960 (after Davis and Karzulovic, 1963).

Figure 25.

Map of area affected by November 1987 El Alfalfal (Rio Colorado) rockslide and ensuing debris flow, Chile (after Casassa and Marangunic, 1993; Hauser, 1993).

Figure 25.

Map of area affected by November 1987 El Alfalfal (Rio Colorado) rockslide and ensuing debris flow, Chile (after Casassa and Marangunic, 1993; Hauser, 1993).

Figure 26.

Maitenes Power House (Fig. 25) on Rio Colorado, Chile, partially buried by debris and mud from El Alfalfa] (Rio Colorado) debris flow of November 1987.

Figure 26.

Maitenes Power House (Fig. 25) on Rio Colorado, Chile, partially buried by debris and mud from El Alfalfa] (Rio Colorado) debris flow of November 1987.

Figure 27.

10-m-diameter boulder from November 1987 El Alfafal debris flow in valley of Rio Colorado, Chile. Boulder was dragged ~14 km by debris flow (photo by A. Hauser, Servicio Nacional de Geologia y Mineria, Chile; Hauser, 1993).

Figure 27.

10-m-diameter boulder from November 1987 El Alfafal debris flow in valley of Rio Colorado, Chile. Boulder was dragged ~14 km by debris flow (photo by A. Hauser, Servicio Nacional de Geologia y Mineria, Chile; Hauser, 1993).

Figure 28.

Map of Rio Barrancas and Rio Colorado area of central Argentina showing location of prehistorically impounded Lago Cari Lauquen and of path of 1914 debris flow that resulted from failure of natural dam.

Figure 28.

Map of Rio Barrancas and Rio Colorado area of central Argentina showing location of prehistorically impounded Lago Cari Lauquen and of path of 1914 debris flow that resulted from failure of natural dam.

Figure 29.

Sketch of Lago Cari Lauquen on Rio Barrancas (Fig. 28), Argentina, and source of prehistoric landslide that dammed river. Sketch shows status of lake after partial failure of natural dam in 1914. Location of outlet of lake is shown by S at left edge (sketch by P. Groeber [1916, Plate VI]).

Figure 29.

Sketch of Lago Cari Lauquen on Rio Barrancas (Fig. 28), Argentina, and source of prehistoric landslide that dammed river. Sketch shows status of lake after partial failure of natural dam in 1914. Location of outlet of lake is shown by S at left edge (sketch by P. Groeber [1916, Plate VI]).

Figure 30.

Map of Serra das Araras, Brazil, landslide disaster area showing zone (inside dashed line) of destruction after rainstorm of January 22 and 23, 1967 (after Jones, 1973).

Figure 30.

Map of Serra das Araras, Brazil, landslide disaster area showing zone (inside dashed line) of destruction after rainstorm of January 22 and 23, 1967 (after Jones, 1973).

Figure 31.

Typical debris avalanche in thin residual soil that occurred in 1967 in Serra das Araras. Brazil (photo by F.O. Jones. U.S. Geological Survey; Jones, 1973).

Figure 31.

Typical debris avalanche in thin residual soil that occurred in 1967 in Serra das Araras. Brazil (photo by F.O. Jones. U.S. Geological Survey; Jones, 1973).

Figure 32.

Landslide failure of new highway in Sena das Araras, Brazil, caused by storm of January 22–23, 1967. Prior to disaster, valley bottom contained village and highway construction camp: these were destroyed by mud-flow in valley that killed several hundred people. Mudflow was ~4 m deep at this location (photo by F.O. Jones, U.S. Geological Survey; Jones, 1973).

Figure 32.

Landslide failure of new highway in Sena das Araras, Brazil, caused by storm of January 22–23, 1967. Prior to disaster, valley bottom contained village and highway construction camp: these were destroyed by mud-flow in valley that killed several hundred people. Mudflow was ~4 m deep at this location (photo by F.O. Jones, U.S. Geological Survey; Jones, 1973).

Figure 33.

February 18, 1967. Bairro Jardim-Laranjeiras landslide. Rio de Janeiro; landslide resulted in destruction of two apartment buildings and death of 110 people (Da Costa Nunes et al., 1979). (March 20, 1967, photo by Ruy Macial, Geo-Rio, Rio de Janeiro.)

Figure 33.

February 18, 1967. Bairro Jardim-Laranjeiras landslide. Rio de Janeiro; landslide resulted in destruction of two apartment buildings and death of 110 people (Da Costa Nunes et al., 1979). (March 20, 1967, photo by Ruy Macial, Geo-Rio, Rio de Janeiro.)

Table 1.

Summary of Catastrophic Landslides in South America, by Country

Country and yearName of landslideTriggering processType of landslideEstimated volume or areaSocioeconomic and/or topographic effectsReferences
Venezuela
1987Rio LimonHeavy rainDebris flows2 × 106m3210 killed, 400 injured, 30,000 homeless.Elizalde et al. (1987); Salcedo and Vignoli (1987); Montes (1989)
1993 and other yearsCaracasHeavy rainSlides and flowsDamaging events several times. Event in 1993: no casualties, but several expensive homes and local street destroyed.Singer (1983); Salcedo (1984)
Colombia
1985Nevado del RuizVolcanic activityDebris flows (lahars)More than 22,000 killed; 3400 ha of farmland buried; destroyed or damaged 2 hospitals, 58 industries, 343 businesses.Herd (1986); Garcia (1988); Voight (1990); Miletti et al. (1991)
1987Villa TinaPond leakageSoil slide20 × 103 m3At least 217 deaths; 80 houses destroyed.Tokuhiro (1988)
1994PaezEarthquakeSlides, avalanches, debris flowsLength of major flows: 120 kmAbout 2000 killed or missing; more than 30,000 displaced; locally, more than 50% of slopes denuded.INGEOMINAS (1994); Martinez et al. (1995)
Ecuador
1983ChunchiRain and/or snow (wettest year of century)1 × 106 m3Killed more than 150; blocked PanAmerican Highway; buried vehicles.Torres (1983); Benitez (1989)
1987ReventadorEarthquakesSlides, avalanches, debris flows75–110 × 106 m3Economic losses: US$1 billion; 1000 deaths; destroyed 40 km of Trans-Ecuadorian pipeline and highway.Hakuno et al. (1988); Ishihara and Nakamura (1988); Schuster (1991); Tibaldi et al. (1995); Schuster et al. (1996)
1993La JosefinaMine excavation and heavy rainRock slide20–25 × 106 m3Slide formed 100-m-high dam of Rio Paute; failure of dam in 33 days caused 10 000 m3/s flood; hundreds of homes and industries destroyed; no casualties.Chamot (1993); Canuti et al. (1994); Ortiz et al. (1994); Plaza-Nieto and Zevallos (1994)
Peru
1941HuarazFailure of moraine dam upstreamDebris flow10 × 106 m3Destroyed 1/4 of Huaraz, killing 4000–6000 people. Debris flow dammed Rio Santa; dam failure caused flood, destroying downstream settlements and farms.Bodenlos and Ericksen (1955); Ericksen et al. (1989)
1945Cerro Condor-SenccaErosional undercuttingRock slide5.5 × 106 m3Formed 100-m-high dam of Rio Montaro, which failed after 73 days, causing flood exceeding 280 m3/s; roads, 13 bridges, and much farmland destroyed.Snow (1964)
1962Nevados HuascaranFailure of hanging glacierDebris avalanche13 × 106 m3Nine small towns destroyed; 4000–5000 people and thousands of farm animals killed.McDowell and Fletcher (1962); Morales (1966); Cluff (1971)
1970Nevados HuascaranEarthquakeDebris avalanche50–100 × 106 m3Yungay and Ranrahirca destroyed, 18 000 people killed. Failure of debris blockage of Rio Santa caused major flood.Cluff (1971); Plafker et al. (1971); Plafker and Ericksen (1978); Keefer (1981)
1971ChungarRock avalanche100 × 103 m3Water wave caused by avalanche destroyed mining camp, killing 400–600 people.Plafker & Eyzaguirre (1978)
1974MayunmarcaLong-term downcutting by Rio MontaroRock slide–debris avalanche1.0–1.6 × 109 m3As many as 317 killed. Debris avalanche dammed Rio Mantaro; dam failed in 43 days, causing major downstream damage.Hutchinson and Kojan (1975); Lee and Duncan (1975); Kojan and Hutchinson (1978)
Chile
1960RinihueEarthquakeSlides, avalanches, debris flowsLargest single slide: 30 × 106 m3Locally, 75% of timber stripped from slopes.Davis and Karzulovic (1961, 1963); Weischet (1963); Ericksen et al. (1989)
1987El Alfalfal (Rio Colorado)Rock slide, avalanche, debris flowSlide/avalanche volume: 2.5–5.5 × 106 m3Debris flow caused 27 casualties, damaged Maitenes hydroelectric plant and under-construction El Alfalfal power plant.Valenzuela and Varela (1991); Casassa and Marangunic (1993); Hauser (1993)
1991AntofagastaHeavy rainDebris flows500–700 × 103 m3Hundreds of casualties; destroyed large number of homes; heavily damaged water-supply system, roads, and railway lines.Van Sint Jan and Talloni (1993)
Argentina
1914Rio Barrancas and Rio ColoradoFailure of ancient landslide damDebris flow and floodVolume: 2 × 109 m3; length: 300 kmTwo small towns devastated; numerous ranches and farms destroyed.Groeber (1916, 1933)
1976Rio EscoipeHeavy rainDebris flowTown of San Fernando de Escoipe almost totally destroyed by 3 m of mud and rock debris.Igarzabal (1979); Wayne (1987)
Brazil
1966–1967Rio de Janeiro and Serra das ArarasHeavy rainSlides, avalanches, flowsDeaths due to landslides and floods in 1966—1000; in 1967—about 1500. Property and industrial damage “inestimable.”Barata (1969); Da Costa Nunes (1969); Jones (1973); Da Costa Nunes et al. (1979)
1988Rio de Janeiro and PetropolisHeavy rainSlides, avalanches, flowsApproximately 300 people killed; many structures destroyed.Nieto and Barany (1988); Ogura and Filho (1991)
Country and yearName of landslideTriggering processType of landslideEstimated volume or areaSocioeconomic and/or topographic effectsReferences
Venezuela
1987Rio LimonHeavy rainDebris flows2 × 106m3210 killed, 400 injured, 30,000 homeless.Elizalde et al. (1987); Salcedo and Vignoli (1987); Montes (1989)
1993 and other yearsCaracasHeavy rainSlides and flowsDamaging events several times. Event in 1993: no casualties, but several expensive homes and local street destroyed.Singer (1983); Salcedo (1984)
Colombia
1985Nevado del RuizVolcanic activityDebris flows (lahars)More than 22,000 killed; 3400 ha of farmland buried; destroyed or damaged 2 hospitals, 58 industries, 343 businesses.Herd (1986); Garcia (1988); Voight (1990); Miletti et al. (1991)
1987Villa TinaPond leakageSoil slide20 × 103 m3At least 217 deaths; 80 houses destroyed.Tokuhiro (1988)
1994PaezEarthquakeSlides, avalanches, debris flowsLength of major flows: 120 kmAbout 2000 killed or missing; more than 30,000 displaced; locally, more than 50% of slopes denuded.INGEOMINAS (1994); Martinez et al. (1995)
Ecuador
1983ChunchiRain and/or snow (wettest year of century)1 × 106 m3Killed more than 150; blocked PanAmerican Highway; buried vehicles.Torres (1983); Benitez (1989)
1987ReventadorEarthquakesSlides, avalanches, debris flows75–110 × 106 m3Economic losses: US$1 billion; 1000 deaths; destroyed 40 km of Trans-Ecuadorian pipeline and highway.Hakuno et al. (1988); Ishihara and Nakamura (1988); Schuster (1991); Tibaldi et al. (1995); Schuster et al. (1996)
1993La JosefinaMine excavation and heavy rainRock slide20–25 × 106 m3Slide formed 100-m-high dam of Rio Paute; failure of dam in 33 days caused 10 000 m3/s flood; hundreds of homes and industries destroyed; no casualties.Chamot (1993); Canuti et al. (1994); Ortiz et al. (1994); Plaza-Nieto and Zevallos (1994)
Peru
1941HuarazFailure of moraine dam upstreamDebris flow10 × 106 m3Destroyed 1/4 of Huaraz, killing 4000–6000 people. Debris flow dammed Rio Santa; dam failure caused flood, destroying downstream settlements and farms.Bodenlos and Ericksen (1955); Ericksen et al. (1989)
1945Cerro Condor-SenccaErosional undercuttingRock slide5.5 × 106 m3Formed 100-m-high dam of Rio Montaro, which failed after 73 days, causing flood exceeding 280 m3/s; roads, 13 bridges, and much farmland destroyed.Snow (1964)
1962Nevados HuascaranFailure of hanging glacierDebris avalanche13 × 106 m3Nine small towns destroyed; 4000–5000 people and thousands of farm animals killed.McDowell and Fletcher (1962); Morales (1966); Cluff (1971)
1970Nevados HuascaranEarthquakeDebris avalanche50–100 × 106 m3Yungay and Ranrahirca destroyed, 18 000 people killed. Failure of debris blockage of Rio Santa caused major flood.Cluff (1971); Plafker et al. (1971); Plafker and Ericksen (1978); Keefer (1981)
1971ChungarRock avalanche100 × 103 m3Water wave caused by avalanche destroyed mining camp, killing 400–600 people.Plafker & Eyzaguirre (1978)
1974MayunmarcaLong-term downcutting by Rio MontaroRock slide–debris avalanche1.0–1.6 × 109 m3As many as 317 killed. Debris avalanche dammed Rio Mantaro; dam failed in 43 days, causing major downstream damage.Hutchinson and Kojan (1975); Lee and Duncan (1975); Kojan and Hutchinson (1978)
Chile
1960RinihueEarthquakeSlides, avalanches, debris flowsLargest single slide: 30 × 106 m3Locally, 75% of timber stripped from slopes.Davis and Karzulovic (1961, 1963); Weischet (1963); Ericksen et al. (1989)
1987El Alfalfal (Rio Colorado)Rock slide, avalanche, debris flowSlide/avalanche volume: 2.5–5.5 × 106 m3Debris flow caused 27 casualties, damaged Maitenes hydroelectric plant and under-construction El Alfalfal power plant.Valenzuela and Varela (1991); Casassa and Marangunic (1993); Hauser (1993)
1991AntofagastaHeavy rainDebris flows500–700 × 103 m3Hundreds of casualties; destroyed large number of homes; heavily damaged water-supply system, roads, and railway lines.Van Sint Jan and Talloni (1993)
Argentina
1914Rio Barrancas and Rio ColoradoFailure of ancient landslide damDebris flow and floodVolume: 2 × 109 m3; length: 300 kmTwo small towns devastated; numerous ranches and farms destroyed.Groeber (1916, 1933)
1976Rio EscoipeHeavy rainDebris flowTown of San Fernando de Escoipe almost totally destroyed by 3 m of mud and rock debris.Igarzabal (1979); Wayne (1987)
Brazil
1966–1967Rio de Janeiro and Serra das ArarasHeavy rainSlides, avalanches, flowsDeaths due to landslides and floods in 1966—1000; in 1967—about 1500. Property and industrial damage “inestimable.”Barata (1969); Da Costa Nunes (1969); Jones (1973); Da Costa Nunes et al. (1979)
1988Rio de Janeiro and PetropolisHeavy rainSlides, avalanches, flowsApproximately 300 people killed; many structures destroyed.Nieto and Barany (1988); Ogura and Filho (1991)
Table 2.

Processes That Most Probably Triggered Catastrophic South American Landslides

Triggering processNumber of occurrences
Heavy or prolonged rainfall10
Earthquake shaking5
Valley downcutting due to long-term erosion3
Failure of natural dam2
Volcanic activity1
Ice avalanche1
Leakage from manmade pond1
Triggering processNumber of occurrences
Heavy or prolonged rainfall10
Earthquake shaking5
Valley downcutting due to long-term erosion3
Failure of natural dam2
Volcanic activity1
Ice avalanche1
Leakage from manmade pond1

Contents

References

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