Glacial Erosional Landforms: Cirques, Tarns, Horns, Arêtes, Glacial Troughs/Fiords
Geography › Geomorphic Processes and Landform Evolution · Topic 3.23
Glaciers are slow rivers of ice that erode by plucking, pulling blocks of rock away as the ice freezes to the bed, and by abrasion, grinding the rock with the stones frozen in the ice. Their erosional landforms include cirques (armchair-shaped hollows), tarns (lakes in cirques), arêtes (sharp ridges between cirques), horns (pyramid peaks such as the Matterhorn), U-shaped glacial troughs, hanging valleys, and fiords (glacial troughs drowned by the sea).
6 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution
At a Glance
- Processes Plucking and abrasion
- Cirque Armchair-shaped hollow at the head of a valley
- Horn Pyramid peak from several cirques
- Trough U-shaped valley
- Fiord Drowned glacial trough
- Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution
Where Does It Fit?
This topic begins the pair on glacial landforms, after the topics on wind and water. It takes up the high mountains and polar lands where ice, not water, is the main geomorphic agent. Previous topic: Karst Depositional Landforms: Stalactites, Stalagmites, Pillars. Next topic: Glacial Depositional Landforms: Glacial Till, Moraines, Eskers, Outwash Plains, Drumlins.
What Is a Glacier and How Does It Move?
In short: a glacier is a river of ice that slowly carves valleys and drops debris.
A glacier is a large mass of ice that forms on land where more snow falls in winter than melts in summer, so that the snow compacts into ice over many years. Once the ice is thick enough, it flows slowly downhill under its own weight and gravity, at a speed from a few centimetres to several metres a day. Glaciers occupy about 10 per cent of the Earth’s land area, mostly in Antarctica and Greenland. The main types are valley or alpine glaciers, confined to mountain valleys; ice sheets or continental glaciers, which cover vast areas such as Antarctica and Greenland; piedmont glaciers, which spread out at a mountain foot; and tidewater glaciers, which end in the sea. The features that moving ice leaves behind are called glacial landforms. The ice carries rock debris and so acts like a huge bulldozer and sandpaper, eroding the land in a way that rivers cannot.
What Are the Erosional Landforms of Glaciers?
| Landform | Description |
|---|---|
| Cirque (corrie, cwm) | An armchair-shaped hollow at the head of a glacier, cut by ice and frost action; may hold a small lake called a tarn |
| Arête | A sharp, knife-edged ridge between two cirques or valleys |
| Horn (pyramidal peak) | A pointed peak left when several cirques cut back into a mountain; the Matterhorn in the Alps is the classic example |
| U-shaped valley (glacial trough) | A valley widened and deepened by a glacier, with steep sides and a flat floor |
| Hanging valley | A tributary valley left high above the main trough; often ends in a waterfall |
| Truncated spur | A river valley spur that is cut off by the passage of a glacier |
| Fjord | A U-shaped valley drowned by the sea; Norway, Chile, New Zealand |
| Roche moutonnée and striations | Smoothed and polished rock outcrops and scratch marks showing the direction of ice flow |
How Do the Main Erosional Landforms Compare?
| Landform | Description | Formation |
|---|---|---|
| Cirque (corrie, cwm) | Armchair-shaped hollow with steep back wall at the head of a glacial valley | Snow collects in a hollow, turns to ice, and plucks and grinds out the rock; the ice rotates as it moves |
| Tarn | Small lake in a cirque after the ice melts | Water fills the rock basin |
| Arête | Knife-edged ridge between two cirques or troughs | Cirques grow back to back and cut away the ridge |
| Horn (pyramidal peak) | Sharp pyramidal peak with three or more faces | Cirques cut into a mountain from several sides; the Matterhorn in the Alps is an example |
| U-shaped valley (glacial trough) | Wide valley with a flat floor and steep sides | A glacier deepens and widens a river valley |
| Hanging valley | Tributary valley whose floor is high above the main trough | The small tributary glacier cut down less; waterfalls often spill from it |
| Fiord | Long, narrow, steep-sided inlet of the sea | A glacial trough drowned by rising sea level; found in Norway, Chile, New Zealand and Alaska |
| Roche moutonnée | Rock hump smoothed on the up-ice side and plucked on the down-ice side | Abrasion and plucking |
How Did Past Ice Ages Shape Landscapes?
During the Pleistocene epoch, which began about 2.6 million years ago, ice sheets repeatedly covered northern North America, northern Europe and parts of Asia. They carved the Great Lakes basins, scoured the Canadian Shield and left the fjords of Norway, and drumlins and moraines across northern Europe and North America. Sea level fell by over 100 metres during glaciation and rose after melting. The present interglacial epoch, the Holocene, began about 11,700 years ago.
Where Are These Features Found and Why Do They Matter?
Cirques and horns are common in the high Himalaya, the Alps, the Rockies, the Andes and Scandinavia. The Himalayan glaciers of Gangotri and Siachen leave large U-shaped valleys, and the Kashmir Valley has glacial features. The valleys of Ladakh and Spiti show glacial troughs and hanging valleys. As an analytical point, many valleys that are now ice-free were shaped by ice in the last glacial period, so the landscape records past climates, as in Pangaea, about 300 to…">Geological History of the Earth. Glacial troughs also make natural routes for roads and sites for hydropower, but are prone to avalanches and glacial lake outburst floods as ice melts under climate change. The deposition made by the same ice is in Glacial Depositional Landforms: Glacial Till, Moraines, Eskers, Outwash Plains, Drumlins.
Why Is This Topic Important?
- Terms Cirque and horn are asked
- India Himalayan glaciers
- Climate Past ice ages and melting
What Came Next?
The next topic describes the depositional landforms of glaciers: till, moraines, eskers and drumlins. Next topic: Glacial Depositional Landforms: Glacial Till, Moraines, Eskers, Outwash Plains, Drumlins.
Key People and Terms
- Cirque Glacial hollow at a valley head
- Tarn Lake in a cirque
- Arête Sharp ridge
- Horn Pyramid peak
- Fiord Drowned glacial trough
- Plucking Pulling out of rock blocks by ice
Exam Corner
Points to Remember
- Glacial valleys are U-shaped; river valleys are V-shaped.
- A tarn lies in a cirque.
- The Matterhorn is a horn.
- A fiord is a drowned glacial trough.
- Glaciers erode by plucking and abrasion.
Do Not Confuse With
- U-shaped and V-shaped valleys Glacier versus river
- Arête and horn Ridge versus peak
- Fiord and ria Drowned glacial valley versus drowned river valley
Memory Hook
Cirque carves, tarn fills, arête slices, horn thrills.
Mains Angle
Questions compare glacial and fluvial landscapes. These points add depth.
- Processes Plucking and abrasion
- Forms Cirque to fiord
- Change Retreating glaciers
A Question You May Face
An original practice question, not a past paper question.
“Describe the landforms produced by glacial erosion and compare a glaciated valley with a river valley.”
How to Answer
- Process Plucking and abrasion.
- Forms Cirque, horn, trough, fiord.
- Compare U versus V.
- Link Himalaya.
GS Relevance
Frequently Asked Questions
What are glacial landforms?
Glacial landforms are those made by moving ice. Erosional ones include cirques, arêtes, horns, U-shaped valleys, hanging valleys and fjords, while depositional ones include moraines, drumlins, eskers, kames, erratics and outwash plains, all of which are best seen in mountain valleys and in northern lands.
What is a cirque?
A cirque, also called a corrie or cwm, is an armchair-shaped hollow with steep walls at the head of a glacier valley. It is carved by ice and frost action and often holds a small lake called a tarn after the ice melts.
How does a U-shaped valley differ from a V-shaped valley?
A V-shaped valley is cut by a river that erodes downward, so it has steep sides narrowing to the bottom. A U-shaped valley is cut by a glacier, which erodes sideways and downward, leaving wide, steep walls and a flat floor.
What is a hanging valley?
A hanging valley is a tributary valley whose floor lies high above the floor of the main glacial trough, so that the stream plunges down as a waterfall. It forms because the large main glacier cut its trough deeper than the smaller tributary glacier could cut its valley.
What is a fiord?
A fiord is a long, narrow, steep-sided inlet of the sea, formed when a glacial trough is drowned by rising sea level after the ice melts. Fiords occur in Norway, Chile, Greenland, Alaska and New Zealand, and often have great depth and high cliffs.
PYQ Practice — Statement Analysis
1 A U-shaped valley is a feature of glacial erosion.
Glaciers widen and deepen valleys.
2 The Matterhorn is a horn formed by glacial erosion.
Several cirques cut back to form it.
3 A tarn is a lake that forms in a cirque.
Water collects after the ice melts.
4 An arête is a pyramid-shaped peak.
That is a horn; an arête is a ridge.
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:
Related Topics
Browse the full Geography index