Geography
Glacial Erosion
Glacial erosion refers to the process by which glaciers carve and shape the land through the movement of ice and meltwater. This process involves the plucking and abrasion of rock and sediment, resulting in the formation of features such as cirques, arêtes, and U-shaped valleys. Glacial erosion significantly impacts the landscape, shaping it over long periods of time.
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11 Key excerpts on "Glacial Erosion"
eBook - PDFPhysical Geography
Great Systems and Global Environments
- William M. Marsh, Martin M. Kaufman(Authors)
- 2012(Publication Date)
- Cambridge University Press(Publisher)
The amount of material eroded from a mountain valley by an alpine glacier over a year, for example, is substantially greater than a large stream could erode from the same valley. Measurements of sedimentation rates on the seafloor reveal that much more sediment is discharged to the oceans during ice ages that during non-glacial periods. Yet, in terms of total work output eroding land worldwide, glaciers are a poor second to runoff and streams, simply because glaciers cover only 10 percent of Earth’s land area. Nevertheless, in those areas where glaciers are or have been, they have profoundly influenced the form and composition of landscape through erosion and deposition. Erosional Processes of Glaciers: Glaciers erode by three main processes: abrasion, crushing, and quarrying. These are illustrated in Figure 23.19, but they need explanation. Abra- sion (also called scouring) involves a rasping action in which rocks carried at the base of the moving ice grind away the underlying bedrock. The result is scratching, grooving, and polishing of bedrock which is accompanied by the production of a fine residue called rock flour, which clouds and discolors meltwater at the front of the glacier. Crushing is a related process involving the fragmentation of boulders under the weight of the ice as the glacier moves over obstacles at its base. Quarrying involves plucking of large pieces of rock from underlying bedrock as the glacier moves over it. The glacier literally freezes onto a block of rock, pulls it out, and entrains it into the base of the ice. Because polar glaciers are frozen fast L a b r a d o r c u r r e n t Greenland Norway 60° 50° 40° 30° United Kingdom Iceland estimated annual maximum extent Canada Ireland exceptional sightings (1831–1972) Gulf Stream East Greenland Current Titanic, 1912 Canary Is.
eBook - PDF- Mateo Gutierrez(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
The pres- ence of this easily eroded material in certain regions must be included in the interpretation of Glacial Erosional landforms and the quantification of ice erosion. The Central Iberian sys- tem, which has thick layers of pre-Quaternary weathering deposits, is an area where this evidence should be part of the study of glacial landforms (Gutiérrez and Rodríguez, 1978). Fracturing and quarrying of the rock substrate, either inherited or of glacial origin, and the availability of loose pre- glacial material are important factors in Glacial Erosion; they are more important than abrasion because abrasion accounts for no more than 40% of total erosion (Hallet, 1996). 13.2.1.1.c Removal of detritus When a glacier slides over its bed, the rate of particle move- ment depends primarily on the size and shape of the parti- cles and the roughness of the substrate. A traction force that exceeds resistance to friction (Sugden and John, 1976) is nec- essary to move a particle. Effective erosional activity removes from the substrate fragments that have been generated by the previously discussed processes. In this way, glaciers erode exposed rock. Subglacial melt water removes some of the detritus (Hallet, 1979; Drewry, 1986). This process is significant beneath temperate glaciers but negligible under polar glaciers. Basal material under temperate glaciers is also moved by the pressure of the ice mass on fragments and small sized water-soaked particles at the rock-ice contact; these flow toward areas of lesser pressure (Rea, 2007). 13.2.2 Landforms produced by Glacial Erosion As a glacier passes over and erodes a surface, it generates various forms. Table 13.2 (Sugden and John, 1976) is a clas- sification of landforms generated by glacial activity. This clas- sification, which is necessarily somewhat subjective, has three categories: unconfined ice flow, ice flow confined within rocky channels, and the interaction of glacial and periglacial activity.
eBook - PDFModern and Past Glacial Environments
Revised Student Edition
- John Menzies(Author)
- 2002(Publication Date)
- Butterworth-Heinemann(Publisher)
131 5 PROCESSES OF Glacial Erosion N. R. Iverson 5.1. INTRODUCTION The basic processes of Glacial Erosion responsible for the spectacular landforms associated with alpine glaciation were identified over a century ago. Forbes (1846) recognized that rock clasts embedded in glacier ice abrade the underlying rock bed, and Tyndall (1864) noted that glaciers quarry rock blocks bounded by joints. Detailed observations of striation patterns and grooves made subsequently by Chamber-lin (1888) established that ice behaves as a deforming fluid rather than a rigid body. These observations helped Gilbert (1903, 1906) relate ice flow at glacier beds to mechanisms of rock fracture and erosion. The most illuminating recent studies of Glacial Erosion have paralleled Gilbert’s pioneering efforts, explicitly linking glaciological theory with the processes that erode the bed. This approach, complemented by observations in the field and laboratory, has provided a fuller understanding of erosional processes than that possible solely from inferences based upon field observations (Plate 5.1). Three mechanisms of erosion are traditionally considered: abrasion, quarrying and the action of subglacial water. Turbulent flow of water in zones where ice has separated from the bed erodes sinuous channels, pot-holes, and elongate crescentic furrows around resistant obstacles on the bed (Sharpe and Shaw, 1989) and dissolution leaves a clear imprint on carbonate bedrock (Hallet, 1976). Despite the local importance of erosion by subglacial water, it is usually considered to be volumetrically subordinate to abrasion and quarrying (Drewry, 1986, p. 90). Unequivocal data in support of this viewpoint are lacking, but the ubiquity of glaciated bedrock smoo-thed by abrasion and roughened by quarrying sug-gests that these two processes are dominant in many PLATE 5.1. Bedrock exhibiting striae and chattermarks. Glacier (Omsbreen, Norway) had flowed from left to right.
eBook - PDFGeomorphology
The Mechanics and Chemistry of Landscapes
- Robert S. Anderson, Suzanne P. Anderson(Authors)
- 2010(Publication Date)
- Cambridge University Press(Publisher)
Again, the goal is not to be encyclopedic, but to address the physics and chemistry of the processes that gave rise to each of the forms. Erosional processes Any visit to a recently deglaciated landscape will reveal clues that it was once beneath a glacier. The bedrock is often smooth, sometimes so smooth that it glints in the sun as if it has been polished. The bed-rock is also commonly scratched. The small bumps have been removed, leaving a landscape dominated by larger bumps and knobs that have characteristic asymmetry. And at the large scale we see U-shaped valley cross sections, hanging valleys, fjords, and strings of lakes dotting the landscape. At an even larger scale, fjords bite through the margins of most continents that have been subjected to repeated occu-pation by ice sheets. Each of these features cries out for an explanation, beyond “this valley was once occupied by a big moving chunk of ice.” 0 250 m/yr (a) (b) Figure 8.39 Antarctic ice speeds documented using inSAR methods, (a) covering all of the continent, and (b) focused on the ice streams draining the West Antarctic Ice Sheet toward the Ross Ice Shelf (after Ian Joughin, image courtesy RADARSAT Antarctic Mapping Project). Erosional processes 245 Abrasion The scratches, called striations, are the products of individual rocks that were embedded in the sole of the glacial ice as it slid across the bedrock. The erosion resulting from the sum of all these scratches is the process called subglacial abrasion. It is abra-sion that smoothes the bed. It is the short wave-length bumps in the bed that are gone, making it look smoother. This should trigger recollection of the regelation process by which glaciers move past small bumps. Consider again that bump, and think about a rock embedded in the ice approaching the bump. The bottom line is that while the ice can get around the bump with its regelation magic act, the rock cannot.
eBook - PDFEarth Science
An Introduction
- Mark Hendrix, Graham Thompson, Mark Hendrix(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
Glacial Erosion 317 ● FIGURE 13.12 Glaciers eroded bedrock to form this string of paternoster lakes in the Tatra Mountains of Poland. Landscape Nature Photo/Shutterstock.com ● FIGURE 13.13 The Matterhorn in Switzerland formed as three alpine glaciers eroded cirques into the peak from three different sides. The sharp ridge between two cirques is called an arête. cge2010/Shutterstock.com Basin formed by glacial weathering and erosion Exposed bedrock is fractured by freeze and thaw weathering; pieces are dislodged and transported downslope by gravity and glacial flow. Cirque ● FIGURE 13.11 (A) A glacier eroded this concave cirque into a mountainside Alberta, Canada, forming Ptarmigan Cirque. (B) To form a cirque, snow accumulates and a glacier begins to flow from the summit of a peak, shown here in cross section. (C) Weathering and Glacial Erosion form a small depression in the mountainside. (D) Continued glacial movement enlarges the depression. When the glacier melts, it leaves a cirque carved in the side of the peak, as in the photograph. 2009fotofriends/Shutterstock.com (A) (C) (D) (B) arête. When the glaciers melt, the arête will form a drainage divide that separates the two adjacent valleys or cirques. Looking downward from our peak, we may see a water- fall pouring from a small, high valley into a larger, deeper one. A small glacial valley lying high above the floor of the main valley is called a hanging valley (●FIGURES 13.9 and 13.14). The famous waterfalls of Yosemite Valley in California cascade from hanging valleys. A hanging valley forms where a small tributary glacier joined a much larger one. The tributary glacier eroded a shallow valley, while the massive main glacier gouged a deeper one. When the Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
eBook - PDF- James Petersen, Dorothy Sack, Robert Gabler, , James Petersen, James Petersen, Dorothy Sack, Robert Gabler(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
The flowing ice of glaciers is an effective and spectacular geomorphic agent on major portions of Earth’s surface. LEARNING OBJECTIVES WHEN YOU COMPLETE THIS CHAPTER YOU SHOULD BE ABLE TO: 19.1 Explain what a glacier is and how glacial ice forms. 19.2 Differentiate the three types of alpine and two types of continental glaciers. 19.3 Describe how glaciers flow. 19.4 Draw a cross section of an alpine glacier, labeling its major surface and subsurface zones. 19.5 Distinguish the two processes of Glacial Erosion. 19.6 Compare four major Glacial Erosional landforms. 19.7 Relate the principal characteristics of glacial sediment. 19.8 List the different types of glacial moraine. 19.9 Discuss what Earth’s glacial environment was like during the Pleistocene Epoch and how that environment influences people today. GLACIAL SYSTEMS AND LANDFORMS A glacier descending from Mount Iliamna, Alaska, onto an adjacent plain. NPS/Buck Mangipane Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 540 C H A P T E R 1 9 • G L A C I A L S Y S T E M S A N D L A N D F O R M S 19-1 Glacier Formation and the Hydrologic Cycle Glaciers are masses of flowing ice that have accumulated on land in areas where the annual input of frozen precipitation, especially snowfall, has exceeded its yearly loss by melting and other processes. Snow falls as hexagonal ice crystals that form flakes of intricate beauty and variety. Snowflakes have a low density (mass per unit volume) of about 0.1 grams per cubic centimeter (0.06 oz/in. 3 ).
eBook - PDF- Charles Fletcher, Dan Gibson, Kevin Ansdell(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
As the ice moves over uneven terrain, portions of the glacier compress and extend, causing changes in the surface topography of the glacier as well as differences in the internal movement of the ice. Glacial sediments are eroded from bedrock through plucking and abrasion. They may fall from surrounding valley walls onto the ice and be carried to the front of the glacier by the internal movement of ice into the zone of wastage. When the ice retreats, the resulting deposit is known as glacial drift. List and describe the ways that glaciers move and deposit sediment. 17-4 Glacial Landforms Are Widespread and Attest to Past Episodes of Glaciation • 461 Kettle lake Terminal moraine Retreating glacier Ground moraine Outwash plain Kame Drumlin field Esker Wayne Lynch/Age Fotostock America, Inc. Carlyn Iverson/Science Source E.R. Degginger/Science Photo Library Marvin Dembinsky/Photo Associates/Alamy FIGURE 17.14 (a) Glacial till is unstratified and unsorted sediment that has been deposited directly by wasting ice. (b) Moraines are deposits of till formerly in direct contact with ice. This photo of a glacier on Bylot Island, Nunavut, shows a terminal moraine and lateral moraine. (c) When valley glaciers coalesce, like those shown from the Kaskawulsh Glacier in the St. Elias range of Yukon Territory, their lateral and medial moraines come together to form strips of sediment (till) on the surface of the ice. It is common to find glaciated landforms composing kame and kettle topography where kettle lakes and kame deposits are spread across the land. Eskers are long, sinuous ridges of sand and gravel deposited by streams that former- ly ran under or within a glacier. As the ice melts, the channel deposits are lowered to the ground and form a ridge known as an esker. The land surface beneath a moving continen- tal ice sheet can be moulded into smooth, elongated forms called drumlins.
eBook - PDF- Alan F. Arbogast(Author)
- 2017(Publication Date)
- Wiley(Publisher)
Glaciers erode through the processes of abrasion (grinding rock) and plucking (pulling rock from the ground). 2. Glacial striations and grooves are produced through abrasion. 3. A roche moutonnée is a streamlined bedrock landform produced by the combined processes of abrasion (on the upstream side) and plucking (on the lee side). 4. Extensive Glacial Erosion occurs in alpine regions. In general, a preglacial landscape is converted to one that is more angular, with sharper ridges, after glaciation. Resulting landforms include cirques, tarns, arêtes, horns, troughs, hanging valleys, and waterfalls. James Balog/Stone/Getty Images FIGURE 17.18 The Matterhorn in Switzerland. This mountain is 4478 m (14,692 ft) tall and has been dramatically sculpted by alpine glaciations. Most of this shaping occurred due to erosion on the sides of the mountain. 400 CHAPTER 17 Glacial Geomorphology: Processes and Landforms Deposition of glacial till can result in very distinctive land- forms. A notable type of till landform is a moraine, which is a winding ridge-like feature that forms at the front or side of a glacier, or between two glaciers. A glacial moraine is a very poorly sorted deposit, ranging from clays to boulders, that appears when sediments are brought forward by the conveyor action within a glacier until they are dropped out of it (Figure 17.21). A well-developed moraine forms only when the ice front or side is stationary for a relatively long period of time. Only then can the persistent internal motion of the ice continu- ally bring forth enough sediment for a visible ridge to grow. The specific classification of any given moraine depends on its spatial relationship to the glacier that deposited its till. Figure 17.22 shows examples of the different kinds of moraines. A lateral moraine forms on the edge of a glacier and is usually best expressed along the sides of alpine glacial troughs.
No longer available |Learn more- James Petersen, Dorothy Sack, Robert Gabler(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
Erosional Landforms of Alpine Glaciation Glacial abrasion leaves striations—linear scratches, grooves, and gouges—where sharp-edged rocks scrape across bedrock (● Fig. 19.14). Striations indicate direction of ice flow long after the ice has disappeared from the landscape. Abrasion and plucking at the base of a glacier work together to form roches moutonnées (from French: roche, rock; mouton, sheep), asymmetric bedrock hills or knobs that are smoothly rounded on the up-ice side by abrasion, with plucking evident on the abrupt down-ice side (● Fig. 19.15). When an alpine glacier first develops in a hollow high in the mountains, its small size results in almost rotational flow lines for the moving ice. In the zone of accumulation at the glacier’s head, ice movement has a large downward component. For ice to reach the toe in the zone of abla- tion a short distance away, an upward component to the flow may be required there. Ice movement, accompanied by weathering and mass wasting, steepens the bedrock wall at the head of the small glacier while it deepens the ● FIGURE 19.12 A valley glacier on Alaska’s Kenai Peninsula displays a blue zone undergoing ablation at lower elevations contrasted with a white zone where ablation has not occurred at the glacier’s higher elevations. The visible contact between the two zones on the photograph is not necessarily the glacier’s equilibrium line, which represents the elevation at which accumulation equaled ablation for the year. What additional information would be needed to assess if the boundary between the white and blue zones on this photo is the glacier’s annual equilibrium line? USGS/Austin Post ● FIGURE 19.13 The Jakobshavn Glacier in Greenland has been retreating since scientists began monitoring it in 1850. The colored lines mark former positions of the glacier’s terminus.
eBook - PDFGeomorphological Processes
Studies in Physical Geography
- E Derbyshire, K. J. Gregory, J. R. Hails, K. J. Gregory(Authors)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
The relative importance of each of the two modes of flow (internal strain and basal sliding) and the absolute value of the internal strain are subject to wide variation with climate, but they also vary within the same glacio-climate province because of the impor-tant effect of ice thickness on the pressure melting point of ice. It follows that knowledge of the thermal regime of glaciers is fundamental to an understanding of the processes of Glacial Erosion, debris entrainment by ice, and glacial deposition. 5.3 CRYONIVAL PROCESSES The cardinal process in cryonival regions is the cyclic phase change to ice of water situated on or within rock and debris masses. It is useful to distinguish those processes that act without significant translocation of material (processes in situ) and those processes that result in debris transport. The latter processes have already been discussed: free-fall, sliding, granular creep, flow, solifluction and surface wash in Chapter 2, wind transport in Chapter 3 and plastic deformation in Section 5.2. The in situ processes which affect both bedrock and soil are freezing and thawing, salt crystal growth and the cracking of the land surface as a result of contraction at very low temperatures. 5.3a Rock disruption The action of gelivation (freeze-thaw) on rock surfaces or rock clasts within heterogeneous debris gives rise to frost-shattering or gelifraction. Marked oscillations of temperature subject rock to stresses which may be strongly directional under the influence of solar radiation and the surface form and structure of the rock mass. Most rocks in the dry state have considerable resistance to such thermal stress, and breakdown resulting from fatigue may take a very long time. The presence of water in the rock greatly accelerates fatigue and the effect of freezing is maximized by the 9 per cent expansion of water in pores, bedding planes and joints.
eBook - PDF- Alan H. Strahler(Author)
- 2013(Publication Date)
- Wiley(Publisher)
The albedo of arctic regions has decreased significantly, resulting in the absorption of more solar insolation. This in turn propels a positive feedback loop that further increases warming, which then accelerates deglaciation at both poles, as well as in alpine environments. Glacial melting is responsible for a series of events that affect the biosphere, hence humankind. In alpine regions, especially the Himalayas, the meltwater has created huge freshwater lakes that can drain suddenly, sending cascades of water down river valleys to flood inhabited areas and affect the lives of hundreds of thou- sands living downslope in India and Nepal. Rising sea level, which is enhanced by the glacial melt, will affect coastal zones, where the majority of the population lives. The influx of large volumes of freshwater from melting ice in Greenland and Antarctica is projected to dis- rupt long-standing ocean current systems that control regional and global weather patterns. The complex interactions among all these factors make it difficult to project the effects of glacial melting with any precision. International cooperation among scientists and policymakers will be critical as the science community learns more about the Earth’s current cli- mate change. Web Quiz Take a quick quiz on the key concepts of this chapter. A Look Ahead Our chapter, which focused on glaciers and the pro- cesses that lead to the development of glacial landforms, described how flowing ice and meltwater leave their distinctive signatures on the landscape. This chapter is the also last in the group in which we reviewed landform- making agents and processes that operate on the surface of the continents, ranging from mass wasting to fluvial action, waves, wind, and glaciers. It is easier to distinguish among the wide variety and complexity of landforms by examining each agent in turn, as we have done here.
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