Cirque
A cirque (French: ). A cirque may also be a similarly shaped landform arising from fluvial erosion.
The concave shape of a glacial cirque is open on the downhill side, while the cupped section is generally steep. Cliff-like slopes, down which ice and glaciated debris combine and converge, form the three or more higher sides. The floor of the cirque ends up bowl-shaped, as it is the complex
The fluvial cirque or
Formation
Glacial-erosion cirque formation
Glacial cirques are found amongst mountain ranges throughout the world; 'classic' cirques are typically about one kilometer long and one kilometer wide. Situated high on a mountainside near the
Cirques form in conditions which are favorable; in the Northern Hemisphere the conditions include the north-east slope, where they are protected from the majority of the Sun's energy and from the prevailing winds. These areas are sheltered from heat, encouraging the accumulation of snow; if the accumulation of snow increases, the snow turns into glacial ice. The process of nivation follows, whereby a hollow in a slope may be enlarged by ice segregation weathering and glacial erosion. Ice segregation erodes the vertical rock face and causes it to disintegrate, which may result in an avalanche bringing down more snow and rock to add to the growing glacier.[4] Eventually, this hollow may become large enough that glacial erosion intensifies. The enlarging of this open ended concavity creates a larger leeward deposition zone, furthering the process of glaciation. Debris (or till) in the ice also may abrade the bed surface; should ice move down a slope it would have a 'sandpaper effect' on the bedrock beneath, on which it scrapes.
Eventually, the hollow may become a large
If two adjacent cirques erode toward one another, an arête, or steep sided ridge, forms. When three or more cirques erode toward one another, a pyramidal peak is created. In some cases, this peak will be made accessible by one or more arêtes. The Matterhorn in the European Alps is an example of such a peak.
Where cirques form one behind the other, a cirque stairway results, as at the Zastler Loch in the Black Forest.
As glaciers can only originate above the snowline, studying the location of present-day cirques provides information on past glaciation patterns and on climate change.[7]
Fluvial-erosion cirque formation
Although a less common usage,.
Yet another type of fluvial erosion-formed cirque is found on Réunion island, which includes the tallest volcanic structure in the Indian Ocean. The island consists of an active shield-volcano (Piton de la Fournaise) and an extinct, deeply eroded volcano (Piton des Neiges). Three cirques have eroded there in a sequence of agglomerated, fragmented rock and volcanic breccia associated with pillow lavas overlain by more coherent, solid lavas.[9]
A common feature for all fluvial-erosion cirques is a terrain which includes erosion resistant upper structures overlying materials which are more easily eroded.
Notable cirques
- Australia
- Blue Lake Cirque, New South Wales, Australia
- Asia
- Chandra Taal, Himachal Pradesh, India
- Cirque Valley, Hindu Kush, Pakistan
- Makhtesh Ramon, Negev desert, Israel
- Western Cwm, Khumbu Himal, Nepal
- Europe (glacial)
- Cadair Idris, Wales
- Circo de Gredos, Sierra de Gredos, Spain
- Cirque de Gavarnie, Pyrenees, France
- Cirque d'Estaubé, Pyrenees, France
- Maritsa cirque, Rila Mountain, Bulgaria
- Malyovitsa cirque, Rila Mountain, Bulgaria
- Seven Rila Lakes cirques, Rila Mountain, Bulgaria
- Banderishki cirque, Pirin Mountain, Bulgaria
- Coire an t-Sneachda, Grampian Mountains, Scottish Highlands
- Karkonosze, Poland
- Coumshingaun Lake, County Waterford, Ireland [10]
- Europe (fluvial)
- Cirque de Navacelles, Grands Causses, France
- Cirque du Bout du Monde, Grands Causses, France
- Cirque du Bout du Monde, Burgundy, France
- North America
- Cirque of the Towers, Wyoming, United States
- Iceberg Cirque, Montana, US
- Summit Lake cirque, and others on Mount Blue Sky, Colorado, US
- Great Basin and others on Mount Katahdin, Maine, US
- Great Gulf, New Hampshire, US
- Tuckerman Ravine, New Hampshire, US
See also
- Cirque stairway – Stepped succession of glacially eroded rock basins
- Glacial landform – Landform created by the action of glaciers
References
Notes
- ^ This concern is not new, see Evans, I.S. & N. Cox, 1974: Geomorphometry and the operational definition of cirques, Area. Institute of British Geographers, 6: 150–53 regarding term usage.
Footnotes
- ^ Chisholm, Hugh, ed. (1911). . Encyclopædia Britannica. Vol. 7 (11th ed.). Cambridge University Press. p. 196.
- ISBN 978-1-4020-4551-6.
- ISBN 978-0-416-68820-7. Retrieved 2010-01-24.
- ^ S2CID 128580365.
- S2CID 10308635.
- ^ "Mt Field National Park: Landforms, Flora and Fauna". Parks and Wildlife Service Tasmania. Archived from the original on 2011-06-09. Retrieved 2009-05-12.
- S2CID 54921081.
- ^ Distinguishing signal from noise: Long-term studies of vegetation in Makhtesh Ramon erosion cirque, Negev desert, Israel ; David Ward, David Saltz and Linda Olsvig-Whittaker; Plant Ecology, 2000, Volume 150, Numbers 1–2, pp. 27–36
- ^ Early volcanic rocks of réunion and their tectonic significance; B. G. J. Upton and W. J. Wadsworth; Bulletin of Volcanology, 1969, Volume 33, Number 4, pp. 1246–68
- ^ John O'Dwyer. "Go Walk: Coumshingaun, Co Waterford". The Irish Times.