Abstract At least 59 rain lahars have occurred on Mayon Volcano, on the Philippine island of Luzon, since its last eruption in 1984. In the southeastern sector of the volcano, where lahar activity has been greatest, we have evaluated the generation of these flows and their effects by measuring lahar-generating rainfall on the slopes during each main typhoon and rain season (September-December) since 1986 and by mapping the adjacent Mabinit and Matanag channels in detail since 1985. Sixteen debris flows occurred during the monitoring period. Each was triggered by a rainfall that lasted at least 1.4 hours, delivered a minimum of 40 mm of rain at an overall rate of 11 mm/h or more, and included at least one 10-min interval during which at least 10 mm fell. The empirical relationship between the threshold values of lahar-triggering rainfall duration (D) and intensity (I) is the power function I 27.3D -0.38 , a substantially higher threshold than one determined for debris flows world-wide. This higher threshold is due to the coarse, granular, and very porous volcaniclastic surface materials, which also render the role of antecedent rain insignificant in generating lahars. Comparable sediment-delivery systems are situated along the ESE (Basud) and SSE (Bonga) radii of the volcano. Each system is composed of a summit ravine with a fan of pyroclastic deposits at its base, and a pair of channels, one along each side of the fan. Only one of each channel pair continues to be a major lahar conduit. Basud Channel, the principal recipient of runoff and sediment from its ravine and fan of the Basud system, experienced the most frequent lahars in the first year after the eruption; however, its principal source of lahar sediment, an ash capping on Basud pyroclastic fan, was depleted very quickly, thus it has experienced debris flows only twice since 1986. Over the same period, 14 debris flows have occurred along Mabinit Channel because its delivery system has the largest catchment area in its sector and includes the largest ravine of the edifice. Bonga Ravine is deeply incised into a composite lava-tephra sequence; strata cropping out in the steep ravine sides avalanche frequently. Debris that collects along the axis of the ravine during the relatively dry months is mobilized into lahars by the first large storms of the typhoon season. Erosion and deposition by lahars keep the active portion of Mabinit Channel narrow and deep. The debris-flow phases of a lahar spread out upon entering a widening stretch of channel, and the thinner lateral portions stop and aggrade while the thicker centra) portions continue moving downchannel, leaving a narrowed channel. Waning-stage or subsequent hyperconcentrated and flood flows cut down through the new debris-flow deposits. A narrow, deep channel results, constricted between the vertical walls of new debris-flow terraces. The terraces also store material for subsequent lahars to erode and incorporate. A debris-flow fan at the end of Mabinit Channel, initially produced by unconfined debris flows during the 1984 eruption, has continued to evolve. The apex of the fan has twice been extended headward by avulsing debris flows, during Typhoons Saling in 1985 and Unsang in 1989. These events have added about 9 percent of area to the east side of the fan. When debris flows stop occurring along a channel such as Matanag Channel, it is quickly widened by laterally eroding floods and hyperconcentrated flows, which also deposit and thus aggrade the channel floor.

Abstract The World Ocean’s 361.059 × 10 6 km 2 area covers the greater part of the earth’s surface and is 2.5 times as large as the area of land. Nearly 84 percent of the southern hemisphere is blanketed by the oceanic waters. Taken together, all the marginal and inland seas constitute another 10 percent of the World Ocean’s surface area. The continents can be thought of as huge islands in the ocean. Therefore, the oceanic processes of matter and energy transformation are of global significance. Until recently marine sedimentation and the laws of oceanic sediment distribution and composition were poorly understood because of the lack of data and samples of deep-sea sediments, and because the distribution and composition of the material suspended in water was virtually unstudied. Some parts of the oceans such as the Arctic and Antarctic were even less explored because of their inaccessibility and great distance from the countries engaged in intensive oceanographic research. The role of oceanic sediments in the history of the Earth is still not clear. However, most investigators believe that geosynclines form in the marginal regions of the ocean, and thus that old geosynclinal deposits are mainly accumulations of marine sediments. During the last few decades new materials have been obtained which must be evaluated, critically correlated and synthesized. The following are among the most important oceanographic achievements of the past several years: New data on the distribution and composition of sediments of the World Ocean have been synthesized as sediment charts for

Abstract The marine sedimentologist inevitably is faced with the necessity of choosing valid names for different sediments as well as their combination into natural groups on the basis of their similarities. Proper nomenclature and classification are extremely important not only for marine geology but also for petrology in general. Attempts to classify sediments into specific groups have marked sedimentology since its early beginnings. Classifications should be based on objective quantitative characteristics of the basic properties which determine the physical, chemical and mineralogical nature of sediment. It is particularly important that the classification have a quantitative basis and not be purely qualitative, as were many old classifications. The classification of marine sediments should not be substituted for that of marine sedimentary facies. This reservation is necessary because the physical and geographical or facies conditions of sediments are emphasized instead of their material composition or structural features in many foreign classifications such as the well-known schemes of Murray and Renard (1891), Krummel (1907), Andree (1920, 1925). Revelle (1944) and other scientists who distinguished pelagic, terrigenous, deep-sea, shallow-water and littoral sediments. In so doing, these workers often placed sediments of very similar or identical composition under extremely different headings of their classifications. Although schemes of this kind may have a certain significance (Nalivkin, 1956), they cannot fully meet the requirements of the petrology of sediments with all their chemical, mineralogical and structural peculiarities. Of course this does not mean that the classification

Abstract The World Ocean, composed of all the seas and oceans, covers 70.8 percent of the earth’s surface. For every square kilometer of ocean basin there exists 0.4 km 2 of subaerial drainage. This determines the fact that the average sedimentation rates in the World Ocean should be two or threefold as low as the average continental denudation rates. The ocean basins have an average depth of 3795 m and a maximum depth of 11,034 m, in the Marianas Trench. On their landward sides the oceanic depressions are bordered by steep, occasionally precipitous continental slopes and gently sloping shelves. Offshore drilling has revealed that rocks of continental type generally underlie the continental shelf and slope, and geophysical data confirm the continental character of the crust. Deeper ocean waters are underlain by crust which is characterized as oceanic, although several localities with intermediate or even continental crust are found, especially underlying marginal seas. With Antarctica as the most obvious exception, the continents form an almost continuous landmass. The watershed of this generalized landmass divides the subaerial surface into two ocean slopes: an Atlantic-Arctic slope which includes 53 percent of all land, and a Pacific-Indian slope composed of the remaining 47 percent (Table 6). Significantly, the combined Atlantic and Arctic oceans is only 30 percent of the ocean surface; thus, a unit area of bottom surface is supplied with a maximum amount of terrigenous sediment. Lands and oceans are distributed unevenly with latitude; the Southern Hemisphere can be characterized as oceanic and

Abstract An important advance in marine geology over the last 10 to 15 years has been the gathering of quantitative data on the distribution of suspended sedimentary material. Data first were obtained for individual seas or for small areas of the seas. In 1952 to 1953 the investigations were expanded to cover the oceans. The first transoceanic section was made in the Indian Ocean from the Antarctic to the Gulf of Aden in 1955 and 1956. A series of meridional sections was made in 1956 and 1957 in the Indian Ocean, including the second trans-oceanic section, from the Antarctic to the Bay of Bengal (Lisitzin, 1959d, 1961b, c). A great body of suspension determinations from both the surface and in vertical sections down to the greatest depths is now available for all the oceans. All the basic suspension data presented here have been obtained with the same methods and are therefore easily correlated .Unfortunately, it is difficult to assimilate the data of some authors because of the differences in their collection methods. Membrane ultrafiltration on 0.7 μ, pore filters was the major technique employed for the quantitative determinations of suspension concentrations. In addition, separation with supercentrifuges was employed widely for samples of surface water. The distribution of the general sedimentary masses as they move from the shores towards the pelagic regions of the oceans is of great sedimentologic interest and is also intimately related to biogenous process. Suspension concentrations are highest in nearshore areas and

Abstract After the basic sediment distribution in the water column has been considered, it is much easier to evaluate the sediment accumulation localities on the ocean bottom. Such calculations are most efficient if the quantity of accumulating total sediment and of its individual components are expressed in the units of the open system, in g/cm 2 /1000 years. This method allows the distinction between actual intensity of sedimentation and the apparent intensity, which is often what is actually obtained when percentage figures are used. To determine the accumulation of solid sediment in units of the open system it is necessary to know a number of parameters: the sedimentation rate, the unit weight of sediment (saturated bulk density), and its moisture content. Unfortunately, physical properties of sediment are seldom determined. Even if sufficient data is available, merely averaging the data for sediment cores is ineffective. Instead, methods employing mean suspended content data and graphic procedures are necessary. The main difficulty which prevents wide use of the method of the open system (absolute masses) is the shortage of stratigraphic or absolute age data for sediment cores. Determinations on single or closely spaced cores by different methods differ appreciably from one another. Because of this very few attempts have been made to employ this method for the 20 years which have elapsed since the possibilities of the method were determined in principle. With the objective of the present report in view all reliable biostratigraphic and absolute age data for marine and oceanic sediments have been generalized

Abstract The size composition of suspensates and bottom sediments is one of the fundamental characteristics which influences both their physical and their chemical properties. Suspensions and sediments are polydispersed, compositionally heterogeneous systems. A considerable part of the fine and coarse particles, particularly unstable biogenous material, is converted from dispersions into true solutions. On the other hand, the formation of tests and shells is accomplished by the conversion of true solutions to the particulate state. Thus the suspended system of the oceans is in permanent flux and is documented by the bottom sediments in space under different climatic conditions, and in time, during Quaternary time and in the geological past. The supply of suspensions from land is subject to zonality which, as shown earlier, is determined by the zonal nature of weathering and the fineness of the material which is produced. In general, the warmer and moister the climate the finer the material contributed from land, and the more severe the climate the coarser the dispersions brought to sea. Zonality also controls the supply of biogenous suspensates. In high latitudes the contribution of fine silica, finer than 50 μ and mainly finer than 10 μ, dominates the biogenic supply. This material compensates, as it were, for the shortage of fine terrigenous material in the same zones. In regions of carbonate sediment formation the supply of particles coarser than 50 μ predominates. The phytoplankton and zooplankton dispersed systems are closely interlinked as food chains. Thus, the dispersed system of the ocean is also

Abstract Terrigenous sedimentation is the accumulation of sediments composed of rock debris or mineral grains as well as of clay minerals. The ocean is an arena of competition for dominance between terrigenous and biogenous sedimentation, although appreciable volcanogenic sedimentation also occurs in some places. Terrigenous sedimentation usually dominates in as much as its annual supply from land is 7 to 10 times greater than the supply of biogenic material. The processes of biogenous and terrigenous sedimentation are so different that it is most reasonable to consider them separately in order to understand Recent sedimentation. Analytical methods for these constituents are also different. To determine the quantity of biogenous material it is usually sufficient to analyze the content of the major biogenous components which are calcium carbonate and amorphous silica and sometimes organic carbon. Other biogenous components are an order of magnitude less abundant than these and can be excluded from the quantitative evaluations. Chemical or X-ray diffraction analyses cannot reveal the genesis of biogenous material. Instead, sediments and their fractions are analyzed for important organisms under a microscope, which is also indispensable for the genetic study of the major mineral groups and their numerous varieties. Mineralogy and petrography help to reveal terrigenous sources and its modes and distances of dispersal. The mineralogical indicators of terrigenous material are widely distributed and thoroughly studied. Trace elements such as titanium, zirconium, thorium, aluminum or compounds such as silicon in silicates, and A1 2 O 3 /SiO 2 ratios have been used successfully in recent years. Finally, when other methods

Abstract According to the sediment classification by predominant component, biogenons sediments are those containing more than 50 percent organic remains. Sediments containing from 30 to 50 percent organic material is termed biogenous-terrigenous. The most important biogenous sediments are two groups: carbonates and silica. In some places these materials are the basic sediment, sometimes composing 95 to 98 percent of the sediment. The organic matter produced by biota is no less important; however, organic carbon contents in deep-sea sediment nowhere exceed several percent. The major role of organic carbon is that of carrier of the free energy for post-depositional sediment diagenesis. Figure 96 shows the distribution of sediments containing more than 50 percent biogenous components. The most extensive areas of the World Ocean bottom surface are covered by terrigenous sediment and red clay which together occupy an area 4 to 10 times as large as that covered by biogenous deposits. It is also noteworthy that the area of carbonate sediment is much greater than that of siliceous sediment. The annual accumulation of biogenous material on the ocean bottom can be determined by the yearly 1361 × 10 6 ton supply of carbonate (1236 × 10 8 CaCO 3 and 125 × 10 6 MgC0 3 ) and 452 × 10 6 ton supply of silica from land. Inasmuch as the salt composition of oceanic water has not changed since Mesozoic time, the annual amount of carbonate and silica contributed from land by rivers should equal the quantity deposited on the ocean bottom.

Abstract Eolian and volcanogenic pyroclastic materials are propagated in very similar ways. However, volcanogenic sedimentation, although obviously dependent on the eolian processes which are about to be discussed, deserves a separate chapter because of its volumetric and geochemical importance. Until recently, ideas about the eolian transportive process was based exclusively on qualitative and random observations of eolian fallout on ships and on land. This information is summarized in papers by Fett (1958) and Yakubov (1946). During the last few decades fundamental new quantitative data have been obtained on the distribution of aerosols associated mainly with radioactive fallout. Methods have been developed for collecting and studying these aerosol tracers, and almost all nations have organized bureaus for monitoring fallout (Spurnyy and others, 1964; Selezneva, 1964; Styro, 1959). These new data permit the creation of new general theories on aerosol fallout which yield basic conclusions of sedimentologic value. Aerosols are distributed in three radically different ways: Local fallout in the vicinity of the sources, exemplified by the ejection of smoke from industrial chimneys. Tropospheric fallout, the medium range transport of aerosols at heights of about 11 km. Stratospheric or global fallout, occasioned when materials such as volcanic products and desert dust attain heights of more than 11 km and are added to the stratospheric reservoir of our planet. In local fallout, the dispersal of dust or pyroclastic material is influenced, apart from wind direction,

Abstract The volcanogenic, or effusive-sedimentary type of deposits includes the unique accumulations in the vicinity of volcanic structures and on adjacent parts of the ocean floor. The effect of volcanism on sedimentation is complex. Liquids, solids and gases are produced by volcanic eruptions. When eruptions occur underwater all the volcanic material including the liquid and gaseous products remain in the water. Many authors think that explosive eruptions in the oceans are impossible at depths greater than 2000 m (Rittman, 1961) or even 500 m (McBirney, 1963). These figures, based on theoretical considerations about the critical pressure of water vapor, appear confirmed by hydro-acoustic data of the “SONAR” Service which, in more than 10 years of activity in tsunami warning and underwater sound recording in the Pacific Ocean has registered no explosive eruptions at great depths, whereas the shallow-depth eruption of the Medsin volcano was recorded simultaneously by several stations. Evidently, most seafloor eruptions are rather quiet. At first glance this conclusion appears to contradict the wide distribution of pyroclastic material near underwater volcanoes. Palagonite, or hydrated volcanic glass, is especially widespread in the Pacific. Current ideas about the composition and quantity of liquid and gaseous volcanic products are incomplete and discordant. It is quite clear, however, that most of these soluble compounds enter the dynamic chemical reservoir of the ocean and lose their volcanogenic identity by mixing with compounds derived from land. The concentration of some elements in ore quantities occurs only where thermal water accumulates, such

Abstract Inadequate study of oceanic sediments accounts for the dominance through the years of a hypothesis which suggests widespread authigenic sedimentation in the oceans. In particular, the deposition on the bottom of chemogenic siliceous material in the form of spherules and other formations, fine particulate calcium carbonate, and the formation of clay minerals on a large scale have been presupposed. During the last few years, the list of verified authigenic minerals in bottom sediments has been increasingly reduced. It can be said that true authigenic sediments, composed mostly of mineral material which precipitate out of the water, are not encountered. Authigenic minerals are not major sediment forming components but instead are admixtures found in sediments in greater or smaller amounts. Many authors place biogenous material such as carbonates and silicates into the category of authigenic minerals. However, biogenous matter is characteristically and genetically distinct, and its separation into a discrete group is most appropriate. Among authigenic minerals the leading role is played by the material formed during diagenesis as well as during submarine weathering especially of ash material. In particular, iron-manganese nodules and microconcretions dealt with voluminously in the literature (Strakhov, 1965; Mero, 1964; Skornyakova and others, 1962; Skornyakova and Andryuschenko, 1964; Arrhenius and others, 1964; Lynn and Bonatti, 1965; Bonatti and Nayudu, 1965) as well as zeolites, mainly phillipsite, are widely distributed. Palagonite is also widespread, the hydration product of volcanic glass formed during the submarine eruptions of basaltic lava (Bonatti, 1963).

Abstract The contribution to the earth’s surface of certain amounts of cosmic material including meteorites, fine particulate meteoritic substances and cosmic dust was first postulated and recognized long ago. However, it was only the beginning of space exploration by rockets and satellites that provided the opportunity for more accurate qualitative and quantitative estimations of the cosmic sediment source. So far, no large meteorite fragments on the ocean bottom have been found. The bulk of cosmic material are black magnetic iron spherules (cryoconite) and glassy tektites, which were only recently discovered in sediments. Magnetic spherules are formed during melting and scattering of meteorites as they pass through the dense atmospheric layers. They are found both at the surface of large meteorites and near meteor craters. Meteoric dust which settled during the fall of the Sikhota-Alin meteorite had the form of spherules 200 to 1 µ in diameter (Kirova, 1961). Similar spherules were collected near Meteor Crater in Arizona (Zaslow and Kellog, 1961). Iron meteorites constitute only 6 to 7 percent of the total number of the meteorites studied. Most meteorites are stone and iron-stone meteorites, or chondrites. No fine particulate matter of corresponding mineralogy has been found in oceanic sediments. The extraterrestrial origin of cryoconite from Greenland ice was first suggested in 1870. At the same time the challenger expedition found a certain amount of such magnetic balls in the deep sea sediments it collected (Murray and Renard, 1891). These materials, disregarded for almost 100 years, have aroused

Abstract Such a brief review of the extensive material on Recent sedimentation in the oceans as this report, even though partially presented in detail by the cartographic material, is inevitably incomplete and declaratory. The tendency of the reader to pick only those materials that are less familiar and objectively reveal the basic laws out of the abundance of data available is quite natural. Despite the great variety and complexity of Recent sedimentation in the oceans caused by the interlacing of many different factors, it is possible to single out of the great number of these factors the leading ones which generally dictate the specific character of sediments. Any suspension and sediment components can be related to climate, land effects and depth of a basin. These three kinds of zonality are the most common and important. They are especially strongly pronounced in oceanic sediments, since the smaller seas usually lie within one zone and their sediment varieties depend to a greater extent on minor local factors. The oceanic basins are not similar in sedimentation conditions and the distribution of bottom sediments. Sedimentation in the Atlantic Ocean, for instance, reveals very many features in common with large marginal basins. The oceanic character of sediments is most extreme in the Pacific Ocean. Oceanic sediments, as can be inferred from the new data, vary in space and time and are often similar to deposits in marginal seas. In particular, it is practically impossible to distinguish between the Recent sediments from the Bering Sea and those

Abstract The World Oceans covers the greater part of the earth’s surface and is 2.5 times as large as the area of land. Nearly 84 percent of the southern hemisphere is blanketed by the oceanic waters. The continents can be thought of as huge islands in the ocean. Therefore, the oceanic processes of matter and energy transformation are of global significance. Originally presented as a series of lectures by Alexander P. Lisitzin.