Glacial Landforms: Cirques, Drumlins, Eskers and Their Spatial Distribution

A. Types of Glaciers

Before examining individual landforms, it helps to understand the types of glaciers:

• Continental Ice Sheets: Vast, dome-shaped glaciers covering entire continents (e.g., Antarctic Ice Sheet, Greenland Ice Sheet). They shape landscapes through massive erosion and create extensive depositional plains.
• Valley (Alpine) Glaciers: Glaciers confined within mountain valleys. They carve the dramatic U-shaped valleys and cirques typical of the Alps, Rockies, Andes, and Himalayas.
• Piedmont Glaciers: Formed when multiple valley glaciers merge at the foot of a mountain range and spread outward.
• Cirque Glaciers: Small glaciers occupying armchair-shaped hollows (cirques) near mountain summits.

B. Glacial Erosion Processes

Glaciers erode bedrock through two main mechanisms:

• Plucking (Quarrying): The glacier freezes onto rock fragments in the bedrock (especially along joints and fractures) and, as it moves, pulls them away. This creates an irregular, jagged, upstream face on rock outcrops.
• Abrasion: The glacier acts like sandpaper — rock fragments embedded in the base of the ice grind against the bedrock, polishing and scratching it. This produces glacially striated and polished rock surfaces (roches moutonnées).

C. Erosional Landforms

• Cirque (Corrie/Cwm): An armchair or amphitheatre-shaped hollow carved into a mountainside at the head of a glacial valley. It forms by a combination of frost action, nivation (erosion under a snow patch), and glacial erosion. The back wall is steep; the floor is a rock basin (sometimes holding a tarn — a glacial lake). A classic cirque lake: Bedni Kund (Uttarakhand, India), Pushkar Lake (contentious — some scholars), and the famous Wastwater in the UK Lake District.
• Arête: A sharp, knife-edged rock ridge formed when two adjacent cirques erode toward each other from opposite sides, eventually leaving only a narrow, serrated ridge between them. Example: the ridges of the Chamonix area in the Alps; numerous ridges in the Zanskar Range (J&K).
• Horn (Pyramidal Peak): When three or more cirques gnaw away at a central mountain from different sides, the result is a steep, pyramid-shaped peak. The Matterhorn in the Alps is the classic example. In India, K2 (though primarily shaped by glaciation and tectonic uplift), Nanda Devi, and several peaks in Himachal Pradesh exhibit this form.
• Tarn: A small, often deep lake that occupies the rock basin of a cirque after the glacier retreats. Tarns are common in glaciated mountain regions worldwide.
• U-shaped Valley (Glacial Trough): Perhaps the most visually distinctive glacial feature. As a glacier moves down a pre-existing river valley, it erodes the valley floor and sides, converting the V-shaped cross-section of a river valley into a characteristic flat-floored, steep-sided U-shape. The valley floor may be deepened into a rock basin that fills with water (ribbon lake / paternoster lake). Example: Zanskar Valley, Spiti Valley (India); Yosemite Valley (USA).
• Hanging Valley: A tributary valley whose glacier was smaller and therefore eroded less deeply than the main valley glacier. After deglaciation, the tributary valley floor is left 'hanging' at a higher elevation than the main valley, with streams tumbling down as spectacular waterfalls. Example: Bridal Veil Falls, Yosemite (USA); numerous tributaries of the Indus and Chenab in Ladakh.
• Fjord: When a U-shaped valley is carved below sea level and later flooded by seawater (following deglaciation and sea level rise), it creates a fjord. Fjords are characterised by deep, narrow, elongated sea inlets with steep, cliff-like walls. Examples: Sognefjord, Norway (world's longest at ~204 km); Milford Sound, New Zealand. India has no fjords.
• Roche Moutonnée: A glacially abraded bedrock knob with a smooth, gently inclined upstream face (stoss side, abraded smooth) and a steep, rough downstream face (lee side, plucked/quarried). They indicate the direction of past ice flow.

D. Depositional Landforms

As glaciers melt or slow down, they deposit their load of sediment (till — unsorted glacial material) and glaciofluvial sediments (sorted by meltwater). This creates a distinctive set of depositional landforms:

• Drumlins: Smooth, elongated, egg-shaped or boat-shaped hills composed of glacial till (sometimes with a rocky core). They occur in swarms ('basket of eggs' topography) and are always oriented with their long axis parallel to the direction of past ice movement. The steeper, blunter end faces upstream; the tapered end points downstream. Formation is debated — most likely shaped when the overriding ice moulded previously deposited till. Examples: Clew Bay, Ireland (hundreds of drumlins); Edina, Minnesota, USA; Rajouri district, J&K (India — limited occurrences).
• Eskers: Long, narrow, sinuous ridges of sorted sand, gravel, and boulders, typically a few metres to tens of metres high and ranging from a few kilometres to over 500 km in length. They are deposited by meltwater streams flowing in tunnels within or beneath the glacier. As the ice melts, the sediment load of these subglacial streams is left behind as a ridge, often winding across the landscape. Eskers are invaluable sources of sand and gravel aggregate. Examples: the Esker of Versailles (Ireland, ~200 km); numerous eskers in Finland (which has some of the world's finest esker systems). In India: limited esker-like features have been reported in the moraine landscapes of Ladakh.
• Moraines: Moraines are ridges or mounds of till, directly deposited by the glacier. Types include:
• Terminal moraine: Marks the maximum extent of glacier advance; a ridge across the valley.
• Recessional moraine: Forms during a temporary halt in glacier retreat.
• Lateral moraine: Ridge along the side of a valley glacier.
• Medial moraine: Ridge along the centre of a glacier, formed when two glaciers merge (merging lateral moraines).
• Ground moraine: A sheet of till deposited beneath and in front of the glacier as it retreats.
• Kames: Irregular, steep-sided hills or mounds of glaciofluvial sand and gravel, deposited by meltwater at or near the glacier's margin or in depressions in the ice surface.
• Kettle Holes and Kettle Lakes: When blocks of glacial ice are buried in outwash deposits and later melt, they leave behind depressions called kettle holes. If these fill with water, they become kettle lakes. The lakes in Ladakh and the numerous prairie potholes of North America (critical waterfowl habitats) are kettle lakes.
• Outwash Plain (Sandur): A broad, gently sloping plain of glaciofluvial sediments deposited by meltwater streams flowing outward from a glacier's snout beyond the terminal moraine. These are sorted, layered deposits — unlike the unsorted till of moraines.

Spatial Distribution in India

India's glacial landscapes are concentrated in the Himalayan and Karakoram ranges:

• Siachen Glacier (Ladakh/Karakoram): The world's second-longest non-polar glacier (~76 km); strategically important and a source of the Nubra River. Site of the world's highest battlefield.
• Gangotri Glacier (Uttarakhand): Source of the Bhagirathi River (Ganga's main tributary); one of the largest in the Himalayas (~30 km). Has retreated over 22 km since 1780.
• Zemu Glacier (North Sikkim): The largest glacier in the Eastern Himalayas (~26 km); feeds the Teesta River.
• Bara Shigri Glacier (Himachal Pradesh): The largest glacier in the Spiti Valley; feeds the Chenab.
• Pindari Glacier (Uttarakhand): Popular trekking destination in the Kumaon Himalayas.

Cirques and U-shaped valleys are well developed in Ladakh, Spiti, and the Zanskar Range. Lateral and terminal moraines are visible across all major Himalayan glaciated valleys. Roche moutonnées and glacial striations are documented in several exposed bedrock areas of Ladakh.

Current Relevance

• Himalayan Glacier Retreat: ISRO's Space Applications Centre and the Wadia Institute of Himalayan Geology have documented accelerated glacier retreat across the Himalayas. The Gangotri Glacier alone has retreated over 22 km since the late 18th century.
• Third Pole Crisis: The Himalayas contain the world's largest freshwater reserves outside the polar regions — often called the 'Third Pole.' Glacier retreat threatens the water supply of over a billion people in Asia.
• National Mission for Sustaining the Himalayan Ecosystem (NMSHE): One of eight missions under the National Action Plan on Climate Change (NAPCC), specifically focused on monitoring and protecting glacial ecosystems.
• Glacial Lake Outburst Floods (GLOFs): As glaciers retreat, glacial lakes (often dammed by moraines) form. When these dams breach suddenly, catastrophic floods result. The Chamoli disaster (February 2021, Uttarakhand), caused by a rock and ice avalanche into the Rishiganga River, highlighted the GLOF hazard in the Himalayas.
• Carbon in glacial till: New research suggests glacial sediments may store significant organic carbon, with implications for carbon accounting in climate models.
• Army and glaciers: India's Siachen Glacier is not just a physical geography landmark but a live geopolitical and military concern — frequently in the news.