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Glacial Landforms UPSC: Erosional and Depositional
Glaciers, massive rivers of ice, have played a pivotal role in shaping Earth’s topography over millennia. Their relentless movement and transformative power create distinctive landforms, categorized broadly into erosional and depositional. Understanding these features is critical for aspirants of the Union Public Service Commission (UPSC) as they form a significant component of the Physical Geography syllabus. This article provides a comprehensive analysis of glacial landforms, emphasizing their formation processes, characteristics, and global examples, with a focus on relevance to competitive examinations.
Table of Contents
Erosional Glacial Landforms
Glacial erosion occurs through two primary mechanisms: plucking and abrasion. Plucking involves the glacier freezing onto bedrock, tearing out rock fragments as it moves. Abrasion refers to the grinding action of ice-entrained debris against the underlying surface, akin to sandpaper. These processes collectively sculpt the landscape into unique erosional features.
Cirques, also known as corries or cwms, are amphitheater-shaped hollows formed at the head of a glacier. They originate from the accumulation of snow in sheltered mountain hollows, which gradually transform into glacial ice. As the glacier grows, rotational movement within the ice deepens the basin, while freeze-thaw weathering at the headwall steepens the back and sides. A tarn lake often occupies the floor post-glaciation. Notable examples include the Cirque de Gavarnie in the Pyrenees and the Nanda Devi Cirque in the Indian Himalayas.
Adjacent cirques eroding a mountain from opposite sides create sharp, knife-edged ridges called arêtes. The Matterhorn in the Swiss Alps exemplifies a pyramidal peak or horn, formed when three or more cirques converge. In India, the Trishul Peak in Uttarakhand showcases similar characteristics.
U-shaped valleys, or glacial troughs, are perhaps the most iconic glacial erosional features. Unlike the V-shaped valleys carved by rivers, glaciers widen and deepen valleys into broad, flat-bottomed troughs with steep, straight sides. The Yosemite Valley in the United States and the Lauterbrunnen Valley in Switzerland are classic examples. In India, the Alaknanda Valley in Uttarakhand demonstrates a U-shaped profile, a testament to past glacial activity.
Smaller tributary glaciers often carve shallower valleys that hang above the main glacial trough, forming hanging valleys. Waterfalls, such as Yosemite Falls, cascade from these elevated valleys. Fjords, submerged U-shaped valleys carved by coastal glaciers, are prominent in Norway, New Zealand, and Chile. India’s Pangong Tso in Ladakh, though a lake, occupies a glacial valley reshaped by tectonic activity.
Roche moutonnée is a rocky outcrop smoothed by glacial abrasion on the upstream side and plucked into a jagged slope downstream. These features indicate the direction of ice flow and are widespread in Canada’s Canadian Shield and Scotland’s Highlands.
Depositional Glacial Landforms
When glaciers retreat, they deposit an assortment of materials collectively termed glacial drift. This includes till, an unsorted mixture of clay, silt, sand, and boulders, and stratified drift, which is sorted by meltwater. Depositional landforms provide insights into past glacial extent and dynamics.
Moraines are ridges of till deposited along glacier margins. Terminal moraines mark the maximum advance of a glacier, forming crescent-shaped ridges across valleys. The Kettle Moraine in Wisconsin and the Rogen Moraine in Sweden are significant examples. In India, the Pir Panjal Range exhibits terminal moraines from ancient glaciers. Lateral moraines form along glacier sides, while medial moraines emerge when two glaciers merge, combining their lateral moraines. Ground moraines, or till plains, are sheets of debris left as the glacier retreats, contributing to fertile agricultural regions like the American Midwest.
Drumlins are streamlined, elongated hills composed of till shaped by overriding ice. They often occur in clusters, termed drumlin fields, with their tapered ends pointing in the direction of ice movement. The Drumlin Belt in New York State and Ireland’s Clew Bay are notable. These features aid in reconstructing paleo-ice flow patterns.
Eskers are sinuous ridges of stratified drift deposited by meltwater streams flowing within or beneath glaciers. They can stretch for hundreds of kilometers, such as the Thelon Esker in Canada. In India, eskers are less common but identified in the Kashmir Valley. Kames, steep-sided mounds of stratified drift, form at glacier margins or in crevasses. Kettle lakes occupy depressions created by buried ice blocks melting within till plains, exemplified by Minnesota’s Lake Itasca.
Outwash plains are expansive, flat areas of stratified drift deposited by meltwater streams beyond the glacier’s terminus. The Skeiðarársandur in Iceland and the Gangetic Plains in India, though primarily fluvial, contain glacio-fluvial deposits from Himalayan glaciers.
Significance and Case Studies
Glacial landforms influence human activities and ecosystems. U-shaped valleys provide fertile soils and routes for transportation. The Swiss Alps and Himalayan valleys support agriculture and tourism. Moraines act as natural dams, creating lakes vital for irrigation and hydropower. Conversely, glacial lake outburst floods (GLOFs) pose risks in the Himalayas, as seen in the 2013 Kedarnath disaster.
India’s Himalayan glaciers, such as Gangotri and Siachen, are critical freshwater reservoirs. Their retreat due to climate change threatens water security for millions. UPSC aspirants must recognize the interplay between glacial dynamics and contemporary issues like sustainable development and disaster management.
Depositional features like drumlins and eskers offer clues to past climates, aiding in paleoclimatology research. The Indian Geological Survey studies these formations to understand Quaternary glaciations and their impact on regional hydrology.
Conclusion
Glacial landforms, both erosional and depositional, are integral to Earth’s geomorphic tapestry. For UPSC aspirants, mastering these concepts necessitates understanding their formation processes, global distribution, and socio-environmental implications. With climate change accelerating glacial retreat, the study of these landforms gains urgency, linking physical geography to pressing global challenges. A thorough grasp of glacial geomorphology not only enriches geographical knowledge but also equips future policymakers to address issues of resource management and environmental sustainability in glaciated regions.