Glacial Depositional Landforms: Glacial Till, Moraines, Eskers, Outwash Plains, Drumlins
Geography › Geomorphic Processes and Landform Evolution · Topic 3.24
Glaciers carry rock debris of all sizes and drop it as the ice melts. The mixed, unsorted material is called glacial till, and it builds moraines: lateral, medial, terminal and ground moraines. Meltwater streams from the ice deposit sorted material in eskers (winding ridges of sand and gravel), kames and outwash plains. Drumlins are oval, streamlined hills of till formed beneath moving ice, and erratics are boulders carried far from their source. India's glaciers such as Gangotri leave moraines at their snouts.
6 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution
At a Glance
- Till Unsorted glacial debris
- Moraines Ridges of till
- Esker Sinuous sand ridge from meltwater
- Drumlin Oval hill of till
- Outwash plain Sorted sand and gravel beyond the ice
- Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution
Where Does It Fit?
This topic follows the one on glacial erosion and covers the deposits left by the same ice. It ends the group of topics on the landforms of glaciers and links to the glaciers of the Himalaya. Previous topic: Glacial Erosional Landforms: Cirques, Tarns, Horns, Arêtes, Glacial Troughs/Fiords. Next topic: Coastal Erosional Landforms: Cliffs, Terraces, Caves, Stacks.
What Are the Depositional Landforms of Glaciers?
- Moraines: ridges of debris carried or dropped by glaciers; terminal moraine at the end of the glacier, lateral moraine along the sides, medial moraine in the centre where two glaciers join, and ground moraine, a sheet of till left behind.
- Erratics: boulders carried far from their source and left in an area of different rock.
- Drumlins: oval, streamlined hills of till, elongated in the direction of ice movement, often in swarms, like an inverted boat.
- Eskers: long, winding ridges of sand and gravel deposited by streams flowing in tunnels under the ice.
- Kames and kettles: mounds of sand and gravel, and depressions left by melting blocks of buried ice, that often become kettle lakes.
- Outwash plain: a broad plain of sorted sand and gravel spread by meltwater streams beyond the ice front.
The material left by glaciers, unsorted, is called till, while meltwater deposits are sorted and layered. The distinction is helpful in Prelims questions.
How Do the Main Deposits Compare?
| Landform | Material | Description |
|---|---|---|
| Glacial till (boulder clay) | Unsorted mix of clay, sand, gravel and boulders | Dropped directly by the ice; no layers |
| Ground moraine | Till | Sheet of till spread under the glacier as it retreats |
| Lateral moraine | Till and rock fallen from the valley sides | Ridge along the edge of the glacier |
| Medial moraine | Till | Ridge down the middle where two glaciers join |
| Terminal (end) moraine | Till | Arc-shaped ridge marking the farthest advance of the ice |
| Drumlin | Till | Oval, whale-back hill, with its long axis along the ice flow; found in clusters called swarms |
| Esker | Sorted sand and gravel | Long, winding ridge laid by a stream flowing in a tunnel under the ice |
| Kame | Sand and gravel | Mound or short ridge deposited by meltwater at the ice margin |
| Outwash plain | Sorted sand and gravel | Flat plain beyond the ice, laid down by meltwater streams |
| Erratic | Boulder | Rock carried far from its source and left on different rock |
Lakes called kettles form in hollows left where blocks of buried ice melted. The hollows scooped out by glaciers fill with water, so that regions such as Finland, Canada and the Alps have thousands of lakes.
What Are the Glaciers of India and Their Hazards?
The Himalayas, Karakoram and Hindu Kush, sometimes called the Third Pole, hold the largest ice volume outside the polar regions. The Siachen Glacier in the Karakoram, about 70 km long, is one of the longest glaciers outside the polar regions. The Gangotri glacier, about 30 km long, in Uttarakhand, is the source of the Bhagirathi, a headstream of the Ganga, and other glaciers are Zemu in Sikkim, Pindari and Milam in Uttarakhand, and many in Ladakh and Kashmir. Himalayan glaciers feed the Indus, Ganga and Brahmaputra systems, as in Geological Regions of India: Deccan Plateau, The Himalayas, Other Peninsular Mountain Ranges, Indo-Gangetic-Brahmaputra Plain, so their melting affects water supply for millions.
Most Himalayan glaciers are retreating because of warming, and meltwater forms lakes behind moraines, which can burst in glacial lake outburst floods, GLOFs. In October 2023 a GLOF from South Lhonak lake in Sikkim damaged the Teesta valley and the Teesta III dam, and in 2013 and 2021 high-mountain disasters affected Uttarakhand. As an analytical point, the retreat of glaciers is a double risk: more water in the short term and floods, but reduced dry-season flow in the long term, so monitoring of glacial lakes and early warning in the valleys below are priorities for disaster management.
Why Do Glacial Deposits Matter?
- Soils and farms: the till and outwash plains of the northern USA, Canada and Europe form fertile farmland, though much of it is stony.
- Resources: eskers and outwash plains are sources of sand and gravel for construction, and moraine lakes feed hydropower.
- Evidence of climate: moraines and erratics show how far glaciers once spread, and map the ice ages, as in Pangaea, about 300 to…">Geological History of the Earth. Terminal moraines mark the places where the ice stopped.
- Hazards: lakes held back by moraine dams in the Himalaya can burst, causing glacial lake outburst floods, such as the South Lhonak Lake event in Sikkim in October 2023.
The erosional forms of glaciers are in Glacial Erosional Landforms: Cirques, Tarns, Horns, Arêtes, Glacial Troughs/Fiords. As an analytical point, glacial deposits, unlike river deposits, are unsorted, and that is the simplest way to tell them apart in the field.
Why Is This Topic Important?
- Terms Moraines and drumlins are asked
- India Glaciers and GLOF hazards
- Evidence Past ice ages
What Came Next?
The next topic moves to the coast and describes the erosional landforms made by waves. Next topic: Coastal Erosional Landforms: Cliffs, Terraces, Caves, Stacks.
Key People and Terms
- Till Unsorted glacial debris
- Moraine Ridge of glacial debris
- Esker Ridge of subglacial stream deposits
- Drumlin Streamlined till hill
- Erratic Out-of-place boulder
- GLOF Glacial lake outburst flood
Exam Corner
Points to Remember
- Till is unsorted; outwash is sorted.
- Terminal moraine marks the glacier’s farthest advance.
- Medial moraine forms where two glaciers meet.
- Drumlins are oval hills of till.
- Eskers are formed by meltwater streams under ice.
Do Not Confuse With
- Esker and drumlin Sorted winding ridge versus unsorted oval hill
- Till and outwash Direct ice deposit versus meltwater deposit
- Lateral and medial moraine Along the edge versus down the centre
Memory Hook
Till is mixed, outwash is sorted; moraine in rows, drumlins in rows.
Mains Angle
Questions ask for glacial features and Himalayan glaciers. These points add depth.
- Forms Moraines, eskers, drumlins
- India Glacier retreat
- Hazard Lake outburst floods
A Question You May Face
An original practice question, not a past paper question.
“Describe the depositional landforms of glaciers and discuss the hazards linked with Himalayan glaciers.”
How to Answer
- Deposits Till and moraines.
- Meltwater Eskers and outwash.
- India Gangotri and Siachen.
- Hazard GLOFs and retreat.
GS Relevance
Frequently Asked Questions
What is a moraine?
A moraine is a ridge or sheet of rock debris carried and deposited by a glacier. Types include terminal moraines at the glacier's end, lateral moraines on its sides, medial moraines where glaciers join, and ground moraines of till spread under the ice.
Which are the major glaciers of India?
The Siachen Glacier in the Karakoram, about 70 km long, is the longest in India. Others include the Gangotri glacier in Uttarakhand, the source of the Bhagirathi, the Zemu glacier in Sikkim, and the Pindari and Milam glaciers in Uttarakhand.
What is glacial till?
Glacial till is the unsorted, unlayered mixture of clay, sand, gravel and boulders that is dropped directly by melting ice. It is different from river deposits because the material is not sorted by size. Till forms moraines and drumlins and covers large areas of the northern continents.
What is an esker?
An esker is a long, winding ridge of sorted sand and gravel, formed by a stream that flowed in a tunnel beneath or within a glacier. When the ice melted, the old stream bed was left as a ridge, often many kilometres in length.
What is a glacial lake outburst flood?
A glacial lake outburst flood, or GLOF, is a sudden release of water from a lake held back by a moraine or ice dam. In the Himalaya, melting glaciers form such lakes, and a burst can send a flood down the valley, as happened at South Lhonak Lake in Sikkim in October 2023.
PYQ Practice — Statement Analysis
1 A drumlin is a winding ridge of sand deposited in an ice tunnel.
That is an esker; a drumlin is an oval hill of till.
2 The Gangotri glacier is the source of the Bhagirathi river.
The Bhagirathi is a headstream of the Ganga.
3 Terminal moraines mark the farthest advance of a glacier.
They are arc-shaped ridges.
4 Glacial till is well sorted by size.
It is unsorted.
Past Mains Questions on This Topic
This topic comes under Geomorphic Processes and Landform Evolution. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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