A cirque is a steep-walled, bowl-shaped hollow carved into a mountainside by a glacier. Often called a corrie in Scotland or a cwm in Wales, it commonly contains a small lake after its glacier melts, and it can mark where a mountain glacier began.
What a cirque looks like
A cirque usually has a curved headwall that rises sharply behind a basin, with a lower lip or threshold at its open end. The basin may be rocky, filled with sediment, or occupied by a lake known as a tarn. The enclosing walls can form a near-amphitheater shape, although real examples vary in size and outline rather than matching a perfect bowl.
Cirques occur high in mountain regions where snow can accumulate and survive from year to year. They may sit below a sharp ridge or summit, and neighboring cirques can cut into opposite sides of the same ridge. Where erosion narrows the ridge into a steep, blade-like crest, the resulting landform is called an arête.
How glaciers carve cirques
A cirque develops as snow collects in a sheltered hollow and gradually compacts into ice. Once thick enough, the ice moves under gravity. Its movement and the processes acting at the glacier’s base enlarge the hollow and steepen its headwall.
Two important processes are plucking and abrasion. Plucking occurs when meltwater enters cracks in bedrock, freezes or refreezes, and helps loosen blocks that moving ice can remove. Abrasion happens as rock fragments carried by the glacier scrape and grind the underlying bedrock. Freeze-thaw weathering and other slope processes also weaken exposed rock, which can then fall onto the glacier or be carried away.
The ice is not simply a static tool grinding a ready-made bowl. The cirque’s shape reflects interacting factors, including the glacier’s movement, local rock structure, water, climate, and the amount of time the ice remains. The glacier may deepen its basin while erosion and rockfalls steepen the headwall. When the ice disappears, the hollow and its surrounding cliffs remain as evidence of past glaciation.
Formation and development
Cirque formation generally begins where snow is repeatedly trapped by topography, such as on a shaded slope or beneath a ridge. Snow that survives summer becomes firn, a dense transitional material, and may eventually become glacier ice. In a sufficiently cold climate, this ice can persist and flow out of the hollow.
As erosion enlarges the hollow, its basin can become deeper than the opening at its lower edge. That raised edge is a threshold, sometimes strengthened by bedrock structure or deposits left by ice. If water later gathers behind it, a tarn may form. A cirque can also exist without a lake: drainage, porous rock, sediment, or later erosion can leave the basin dry.
Not every hollow that resembles a cirque was carved entirely by a glacier. Weathering, landslides, and other processes can create or modify mountain hollows. Geologists therefore consider the wider landscape—such as nearby glacial valleys, polished bedrock, and deposits—rather than identifying a landform by appearance alone.
Cirques in a glacial landscape
Cirques are one part of a larger set of landforms produced by mountain ice. A glacier that flows out of a cirque may occupy a U-shaped valley, whose broad floor and steep sides contrast with the narrower V-shaped valleys commonly cut by rivers. Several cirques can erode toward one another, leaving a sharp peak called a horn or a narrow arête between them.
- Cirque: a glacially eroded basin at the head of a mountain valley.
- Arête: a narrow, steep ridge often formed between neighboring glacial hollows or valleys.
- Horn: a pointed peak shaped by erosion from several cirques.
- Tarn: a mountain lake occupying a cirque basin, often behind a rock threshold or a deposit.
These features are related but not interchangeable. A tarn is water in a basin, not the basin itself, and a cirque is not simply any lake beneath cliffs. The landform’s glacial origin and position at the head of a mountain valley are central to the term.
Where cirques are found and what they reveal
Cirques occur in mountain ranges around the world, including the Alps, the Andes, the Himalaya, and parts of North America and northern Europe. Their distribution reflects where past or present mountain glaciers could form. Today, some cirques hold active glaciers, while others contain lakes, snowfields, or bare rock.
A cirque can help researchers reconstruct former glaciation. Its elevation and orientation, along with evidence from surrounding landforms, can indicate where ice accumulated and how glaciers shaped a region. However, one cirque alone does not provide a precise record of climate: local shade, wind-driven snow, rock type, and drainage also affect its development.
Frequently Asked Questions
Is a cirque the same as a corrie or cwm?
They are regional terms for the same general type of glacial hollow. “Corrie” is commonly used in Scotland, while “cwm” is a Welsh term; “cirque” is widely used in geographical writing.
Does every cirque contain a lake?
No. A lake, or tarn, may form where water is held by the cirque’s threshold, but some basins drain away or remain rocky and dry.
How is a cirque different from a U-shaped valley?
A cirque is a bowl-like hollow near the head of a mountain glacier. A U-shaped valley is a longer trough carved as glacier ice moves down a valley.
Can cirques form where glaciers no longer exist?
Yes. Many are glacial landforms left behind after the ice that carved them retreated or melted. Their present-day appearance can include bare rock, snow, or a tarn.
What is the difference between a cirque and a tarn?
A cirque is the landform: the hollow and its steep enclosing walls. A tarn is a lake that occupies such a hollow. A cirque may have no tarn, and the lake is not what defines the cirque.
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