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Abstract The long, cold winters and short, cool summers in the polar regions result in the formation of a layer of frozen ground that does not completely thaw during the year. This perennially frozen ground, known as permafrost, affects many human activities in the Arctic, as well as in the Subarctic and at high altitudes, and causes problems that are not experienced elsewhere. Permafrost is a naturally occurring material that has a temperature below 0°C continuously for two or more years (Muller, 1943, p. 3). This layer of frozen ground is designated exclusively on the basis of temperature. Part or all of its moisture may be unfrozen, depending upon the chemical composition of the water or depression of the freezing point by capillary forces. For example, permafrost with saline soil moisture, such as that found under the ocean immediately off the arctic shores, might be colder than 0°C for several years but would contain no ice and thus would not be firmly cemented. Most permafrost is consolidated by ice; permafrost with no water, and thus no ice, is termed dry permafrost. The upper surface of permafrost is called the permafrost table. In permafrost areas, the surficial layer of ground that freezes in the winter (seasonally frozen ground) and thaws in summer is called the active layer. The thickness of the active layer under most circumstances depends mainly on the moisture content; it varies from 10 to 20 cm in thickness in wet organic sediments to 2 to 3 m in well-drained gravels. Permafrost is a widespread phenomenon in the northern part of the Northern Hemisphere, underlying an estimated 20 percent of the land surface of the world (Fig. 1).

Abstract Subsurface water affects near-surface processes and landforms in a wide variety of ways. Its essential role in weathering, soil development, slope failure, and karst topography has long been acknowledged. However, its importance in other aspects of the development of landforms has just begun to be recognized in the last decade or so. In this chapter we discuss some major aspects of ground-water geomorphology and ways in which subsurface water can shape the Earth’s surface. In the next chapter, D. C. Ford, A. N. Palmer, and W. B. White discuss the special conditions of karst landforms; in this chapter we discuss other aspects of the role of underground water in landform development. This chapter is organized as follows: first, some effects of water in the vadose or unsaturated zone above the water table, with emphasis on weathering and soil development and their influence on landscape (by Pavich), mass wasting and slope failure (Dietrich and Rogers), and hillslope hydrology (Dunne), with its influence on piping and pseudokarst (Parker) and on development of hillslopes and gully heads (Higgins). Next, the role of water in the saturated zone at or beneath the water table, and its effects on permafrost and pseudokarst (Sloan), land subsidence (Péwé), spring sapping and valley network development (Baker), submarine landforms (Robb), sea cliffs (Norris), scarp retreat (Higgins), and surface stream channels (Keller). Finally, ways are considered in which regional geomorphology can control groundwater behavior and hydrology (Coates).

Abstract The Alaska Range is a glacially sculptured, arcuate mountain wall extending west and southwest 600 mi (1,000 km) in central Alaska from the Canadian border to the Aleutian Range. It is extremely rugged and includes Mt. McKinley (20,443 ft; 6,195 m elevation), the highest mountain on the North American continent. The Delta River, 75 mi (125 km) long, originates on the south side of the range in the Tangle Lakes and flows northward through the range to the Tanana River. The Richard-son Highway (Fig, 1) crosses the range through the Delta River valley, which is 0.6 to 12 mi (1 to 20 km) wide and 60 mi (100 km) long. Because of the lack of villages, cities, and towns, references to geographical points in the valley have been referenced to mile posts on the Richardson Highway since the early part of this century. This practice will be continued in this report. Mile O on the highway is at Valdez, a town on the Gulf of Alaska and the terminus of the Trans-Alaska Pipeline System; the highway ends at mile Fairbanks 363.8.

Abstract The Alaska Range is a glacially sculptured, arcuate mountain wall extending west and southwest 600 mi (1,000 km) in central Alaska from the Canadian border to the Aleutian Range. It is extremely rugged and includes Mt. McKinley (20,443 ft; 6,195 m elevation), the highest mountain on the North American continent. The Delta River, 75 mi (125 km) long, originates on the south side of the range in the Tangle Lakes and flows northward through the range to the Tanana River. The Richard-son Highway (Fig, 1) crosses the range through the Delta River valley, which is 0.6 to 12 mi (1 to 20 km) wide and 60 mi (100 km) long. Because of the lack of villages, cities, and towns, references to geographical points in the valley have been referenced to mile posts on the Richardson Highway since the early part of this century. This practice will be continued in this report. Mile O on the highway is at Valdez, a town on the Gulf of Alaska and the terminus of the Trans-Alaska Pipeline System; the highway ends at mile Fairbanks 363.8.

To be transported far from their place of origin, dust particles must have terminal sedimentation velocities (corresponding to particle size, shape, and density) that are small compared to the root-mean-square velocity fluctuations of the supporting air. Measurements of size distribution changes with height above eroding soil surfaces confirm this. Size distribution of dust obtained by aircraft in the southwestern United States, hundreds of kilometres from the source region, show that the diameters of the largest particles range between 0.02 and 0.1 mm. In studying the production of dust, both aerodynamic and soil relationships must be considered. The partitioning of stress to nonerodible elements, for example, is an important physical mechanism in determining the threshold wind speed at which soil is eroded. Another important factor in the initiation of wind erosion is the strength of the aggregation of the soil. Measurements of the vertical flux of particles smaller than 0.02 mm above eroding soils show a sharp increase of dust production with wind speed. Soils that contain fine material (silt and clay) tend to produce more fine dust than coarse soils do for an equal amount of total soil erosion. For fine-textured soils, the history of the soil is important in determining fine-particle emissions by erosion. For example, aggregates formed in a clay soil that had been water-soaked and dried were very resistant to breakage, whereas aggregates in the same soil that had been subjected to high winter winds and drouth were more easily broken. Field observations of fine particle emissions are related to total soil movement and, by Agricultural Research Service empirical formula, to soil and wind conditions. Wind-tunnel simulations of erosion as well as high-speed measurements of concentration versus time in observed wind erosion are used to illuminate the problem of wind erosion of arid soils.

Quartz was isolated in the fine silt fraction (1 to 10 μ m in diameter) from atmospheric aerosols, wind-erosive and loessial soils, shales, and Pacific pelagic sediments of the Northern and Southern Hemispheres. Its oxygen isotopic ratio ( 18 O/ 16 O) was determined by mass spectrometry to trace provenance or origin in a study of dust sequestering of 137 Cs and other nuclear fission products. Quartz origin from two sources was established: (1) weathered igneous and metamorphic rocks and (2) low-temperature authigenic sources such as chert. High-temperature quartz preferentially accumulates in beach sands, while it decreases in finer particle sizes and in deposits farther from shore. Low-temperature authigenic quartz (for example, chert) increases in fine silt in central marine basin sediments, with δ 18 O= 17 to 24‰. Glacial and fluvial erosion carried predominantly igneous and metamorphic quartz from the suture highlands of the South Polar supercontinent, Gondwanaland, onto continental shelves during late Paleozoic-early Mesozoic time. Quartz of aerosol dust of these uplifted shelves (continents that drifted northward in Cretaceous time) and in the South Pacific pelagics has mainly δ 18 O = 13 ± 2‰. Concurrently, present Northern Hemisphere continents moved across tropical and equatorial climates under which weathering caused great desilication of soils, leaching of soluble Si(OH) 4 into rivers and seas, and accumulation of biogenic silica. The latter subsequently was crystallized into fine quartz silt of chert and other authigenic materials. A high proportion of low-temperature, high-δ 18 O (mainly 19 ± 2‰) quartz occurs in North Pacific pelagic sediments and in sediments and soils of the plains of now Northern Hemisphere continents, in contrast to the situation in the mid- and high-latitudes of the Southern Hemisphere.

A series of haze bands over Barrow, Alaska, in April and May 1976 was found to consist of crustal dust. The bulk elemental composition of the particles was crustal or nearcrustal; the particles had angular shapes, some of which were characteristic of micas; most of their mass was in the giant-particle range, a characteristic of airborne soils; most of the larger particles were rich in silicon and aluminum. The mass-median radius of the particles (2 μ m) indicated that they had probably traveled more than 5,000 km from their source, thereby effectively eliminating Alaska itself as a source. Trajectory analysis showed that the hazecontaining air had passed over the arid and semi-arid regions of eastern Asia a few days earlier, when intense dust storms had occurred there. One of the strongest of these storms, the cloud of which could be traced (by dust reports) from China past Japan and Korea and out over the Pacific Ocean, has been tentatively identified as the source of the Alaskan haze. The Asian dust layers, however, did not seem to increase the local atmospheric turbidity at Barrow. Rather, the turbidity decreased somewhat during the episode and sharply thereafter. The decrease in turbidity accompanied a temporary migration of the jet stream to near the North Pole, which allowed clean Pacific air from far to the south to sweep over Barrow. The high prehaze turbidities, which are characteristic of Barrow air during winter and spring, were associated with Arctic air from the north, which contained much higher concentrations of pollutants than did the southern air after the haze bands. Recent evidence strongly suggests that anthropogenic aerosol is responsible for much of this Barrow haze. It thus seems that distant natural and anthropogenic aerosol sources may affect the radiation balance of the Arctic.

Measurements show that in many ocean regions the major aerosol constituent is mineral matter derived from the continents. The greatest concentrations of soil aerosol particles are found over marine areas “downwind” from arid regions and deserts. Because of the transport of soil material out of North Africa, the Arabian Peninsula, and India, the geometric mean mineral aerosol concentrations over the tropical North Atlantic, the Indian Ocean, and the Mediterranean were at least an order of magnitude greater than those over the Pacific Ocean and the North and South Atlantic. The concentration of soil aerosols in these regions produces highly turbid sky conditions. The relationship between the concentration distribution of soil aerosols over the oceans and that of haze suggests that climatological records of the frequency of occurrence of haze at sea may be useful for delineating those oceanic regions where soil aerosol transport might be most significant.

The Sahara Desert is one of the major sources of atmospheric mineral dust that is transported long distances. The westward transport is discussed by means of a two-dimensional, steady-state transport model and measurements in surface air across the North Atlantic. The model is based on the specific flow conditions for this area and considers sedimentation and turbulent diffusion of dust particles. During preferential transport above the trade wind inversion layer, the aerosol is strongly depleted of particles with r > 1 μ m within 1,000 km from the source. Particles with 0.1 μ m ⩽ r ⩽ 1.0 μ m are only inappreciably removed from the dust plume. Actual mineral aerosol mass concentrations and size distributions seem to be approximated best by the model when one assumes a power-law size distribution at the source with ν * = 2 for particles with 0.1 μ m ⩽ r ⩽ 20 μ m. Based on this assumption and supported by turbidity measurements, an annual mass budget has been calculated for Saharan dust transported over the North Atlantic for various distances from the source. About 260 × 10 6 tons of mineral dust per year leave the Sahara westward. Deep-sea sediment data show no basic discrepancy with values predicted by the model.

Earth-based observations and spacecraft results show that aeolian processes are currently active on Mars. Analyses of various landforms, including dunes, yardangs, and mantling sediments of probable aeolian origin, suggest that aeolian processes have been important in the geological past. Dust storms originate in specific areas of Mars and are most vigorous during the martian summer in the southern hemisphere. In order to understand aeolian processes in the low surface pressure (∼7 mb), carbon dioxide atmosphere of Mars, a special wind-tunnel was fabricated to carry out investigations of the physics of windblown particles under martian conditions. Martian threshold wind speeds have been derived for a range of particle diameters and densities; the threshold curve parallels that for Earth but is offset toward higher wind velocities by about an order of magnitude. The “optimum” size particle (the size most easily moved by minimum wind) is about 100 pm in diameter; minimum freestream winds to generate particle motion are about 40 ms-I. Grains smaller than 100 pm (“dust”) require increasingly higher winds to initiate threshold; yet, estimates of grain sizes in the dust clouds are in the size range of a few microns and smaller. Because the Viking Lander has recorded winds no stronger than those for minimum threshold, it is suggested that some other mechanism than uniform strong winds is required for “dust” threshold. Experiments and theoretical considerations suggest that such mechanisms could be cyclonic (“dust devil”) winds, a saltation cascading effect by larger (more easily moved) particles, and injection of fine grains into the wind stream by outgassing volatiles absorbed on the grains.

The strong winds of the first winter storm to reach the drouth-stricken High Plains in February 1977 caused the largest dust storm yet observed by geostationary orbit environmental satellites (GOES). Two dust plumes, one in eastern Colorado-western Kansas, another near the Texas-New Mexico border, were first observed on GOES-1 images taken at 1700 GMT February 23, and the east-south-eastward progression of the dust pall was observed on later images. By 2030 GMT February 24, dust totally obscured about 400,000 km 2 of ground surface in the south-central United States, as seen on satellite pictures. By 1600 GMT February 26, a discrete dust pall was still visible over the mid-Atlantic Ocean. The enormity of this single dust storm and the historical recurrence of such events suggest that atmospheric transport of dust eastward from the Great Plains to the Atlantic Ocean is of sedimentologic significance. One point source of the dust, the Clovis-Portales area, New Mexico, has a long history of episodic aridity and associated eolian activity that extends from Tertiary time to the Dust Bowl events of the 1930s and similar occurrences during the 1950s. The authors have investigated wind erosion and deposition due to the February 1977 storm by aerial and ground reconnaissance of this area, which is in the windiest part of the southern High Plains. During the 1977 storm, plowed fields were locally eroded to depths of greater than 1 m, and myriads of small yardangs were formed. Fine sand winnowed from certain vulnerable soils was deposited in lobate sheets from several centimetres to more than a metre deep that extended several kilometres downwind from the plowed fields and blowouts. Several key factors contributed to the severe effects of the storm. A persistent Pacific high-pressure ridge, which had diverted earlier storms northward, contributed to a prolonged drouth in the Great Plains. Breakdown of this high permitted passage of the first winter storm into the region, accompanied by very strong winds. Soils of the Portales Valley, composed mainly of eolian sand, silt, and clay, were unusually dry and vulnerable to the wind, which accelerated suddenly on the morning of February 23. The erosive power of the wind in that area may have been further enhanced as it blew upward over the cap-rock escarpment of the Llano Estacado. Other factors that probably contributed to the severity of wind damage from this storm included certain land-use practices that had resulted from a coincidence of economic conditions and governmental policies.