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26-562: There are only a small number of glaciers in the Genaldon River's basin, the largest being Maili at approximately 6.8 km (2.6 sq mi) in area. The Kolka Glacier, located next to Maili, is a cirque / valley glacier , with some hanging parts. Kolka is fed by avalanches and collapses of firn and ice all year round. Its lowest and highest points are located at 3,000 m (9,800 ft) and 3,450 m (11,320 ft) above mean sea level respectively. More than two-thirds of

52-638: 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. Although

78-496: A 9 km stretch of the valley floor was buried underneath a mass of ice and rocks. Its thickness at times approached 50 m, the scouring of the valley slopes reaching a height of 100 m. The estimated volume of ice that was ejected into the valley, obstructing the gorge, was in excess of 100 million m. The mudflow speed averaged 60–70 km/h, peaking at 100 km/h. At least 32 people were killed. Another notable surge started on September 28, 1969. Because its onset occurred during

104-514: A colder season with minimal presence of meltwater in the glacier's basin, the event was not catastrophic. By October 4, Kolka's tongue again reached the Maili glacier, having moved 1.3 km. After a month of relative calm, the glacier was on the move again by the beginning of November. A mass of fractured ice, 100–130 m thick, blocked the Upper Karmadon Springs and moved into the upper parts of

130-577: 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 bowl shape in the side of the mountain, with the headwall being weathered by ice segregation, and as well as being eroded by plucking . The basin will become deeper as it continues to be eroded by ice segregation and abrasion. Should ice segregation, plucking and abrasion continue,

156-487: A less common usage, the term cirque is also used for amphitheatre-shaped, fluvial-erosion features. For example, an approximately 200 square kilometres (77 sq mi) anticlinal erosion cirque is at 30°35′N 34°45′E  /  30.583°N 34.750°E  / 30.583; 34.750  ( Negev anticlinal erosion cirque ) on the southern boundary of the Negev highlands . This erosional cirque or makhtesh

182-412: A mountainside near the firn line , they are typically partially surrounded on three sides by steep cliffs . The highest cliff is often called a headwall . The fourth side forms the lip , threshold or sill , the side at which the glacier flowed away from the cirque. Many glacial cirques contain tarns dammed by either till (debris) or a bedrock threshold. When enough snow accumulates, it can flow out

208-440: Is formed by intermittent river flow cutting through layers of limestone and chalk leaving sheer cliffs. A common feature for all fluvial -erosion cirques is a terrain which includes erosion resistant upper structures overlying materials which are more easily eroded. 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

234-479: Is most often overdeepened below the level of the cirque's low-side outlet (stage) and its down-slope (backstage) valley. If the cirque is subject to seasonal melting, the floor of the cirque most often forms a tarn (small lake) behind a dam, which marks the downstream limit of the glacial overdeepening. The dam itself can be composed of moraine , glacial till , or a lip of the underlying bedrock . The fluvial cirque or makhtesh , found in karst landscapes,

260-416: 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 convergence zone of combining ice flows from multiple directions and their accompanying rock burdens. Hence, it experiences somewhat greater erosion forces and

286-412: The ablation zone's surface is covered by a morainal layer up to 1 m (3 ft 3 in) thick. This and other features, such as relatively gentle slopes, a deep cirque and the presence of a lateral moraine restricting the ice flow and forcing it to make a sharp turn, makes the glacier very prone to accumulation of subglacial meltwater. Historically, the local population have been well aware of

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312-469: The leeward slope of a mountain, where it is sheltered from wind. Rock fall from above slopes also plays an important role in sheltering the snow and ice from sunlight. If enough rock falls onto the glacier, it may become a rock glacier . Randklufts may form beneath corrie glaciers as open space between the ice and the bedrock, where meltwater can play a role in deposition of the rock. Cirque A cirque ( French: [siʁk] ; from

338-549: The Genaldon valley, travelling at 20–50 m per day. By January 1970 it had stopped but, by then, the glacier had extended its length by 4.1 km and descended 800 m. The most catastrophic surge to date occurred on September 20, 2002, when a mass of ice, water and rocks streamed down a 4 km stretch of the valley with an icy mudflow traveling a further 12 km. Ice within the debris began to melt almost immediately, creating new lakes and flooding some settlements which, contrary to

364-452: The Latin word circus ) is an amphitheatre -like valley formed by glacial erosion . Alternative names for this landform are corrie (from Scottish Gaelic : coire , meaning a pot or cauldron ) and cwm ( Welsh for 'valley'; pronounced [kʊm] ). A cirque may also be a similarly shaped landform arising from fluvial erosion. The concave shape of a glacial cirque

390-451: The bergschrund changes very little, however, studies have shown that ice segregation (frost shattering) may happen with only small changes in temperature. Water that flows into the bergschrund can be cooled to freezing temperatures by the surrounding ice, allowing freeze-thaw free mechanisms to occur. If two adjacent cirques erode toward one another, an arête , or steep sided ridge, forms. When three or more cirques erode toward one another,

416-572: The dangers associated with the glacier, which is evident in the unusual locations of the auls . Most settlements of the Caucasus Mountains valleys were built on the valley floor, however, all the old auls of the Karmadon Valley were built on the valley slopes or even on the crests of the nearby ridges. More recently however, a number of settlements have been built on the valley floor. The first well-documented surge occurred on July 3, 1902, in

442-406: The dimensions of the cirque will increase, but the proportion of the landform would remain roughly the same. A bergschrund forms when the movement of the glacier separates the moving ice from the stationary ice, forming a crevasse. The method of erosion of the headwall lying between the surface of the glacier and the cirque's floor has been attributed to freeze-thaw mechanisms. The temperature within

468-542: The end of June, the heavily cracked glacier tongue was seen in a narrow gorge next to the Maili glacier. The tongue then partially collapsed, temporarily damming the river. A pulp of ice, water and morainal material then formed a mudflow which streamed down the river's course, stopping near the Tmenikau aul high on the valley slope. The glacier, which was still on the move, then blocked the gorge causing it to fill up with meltwater. A second mudflow surge occurred on July 6 when

494-401: The glacier leaving behind an empty cirque , a phenomenon not previously observed anywhere else. The large amount of subglacial water resulted in a surge so powerful, that the glacier was practically ejected from its basin. Nonetheless, it reappeared only 2 years later and is currently growing again. Cirque glacier A cirque glacier is formed in a cirque , a bowl-shaped depression on

520-497: The midst of an unusually hot summer, when the mean temperature was 2.7 °С higher than normal. A series of heavy rains occurred in June and early July, filling the river basins with rain and melt water and by the middle of June, a tongue of the Kolka glacier was on the move. Loud crackling was heard in the nearby settlements and, at times, the Genaldon river was turned into a stream of black mud. By

546-481: The old traditions, had been built on the valley floor. The height of the mudflow peaked at 140 m, with the height of the debris near the wall of the Skalisty Ridge reaching 100 m. The village Nizhniy Karmadon, along with several rest houses beside the river were obliterated. At least 125 people were killed and many others were injured. The village has not been rebuilt. The surge resulted in the complete destruction of

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572-524: The opening of the bowl and form valley glaciers which may be several kilometers long. 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,

598-448: The side of or near mountains. Snow and ice accumulation in corries often occurs as the result of avalanching from higher surrounding slopes. If a cirque glacier advances far enough, it may become a valley glacier . Additionally, if a valley glacier retreats enough that it is within the cirque, it becomes a cirque glacier again. In these depressions, snow persists through summer months, and becomes glacier ice. Snow may be situated on

624-472: 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. Eventually, this hollow may become large enough that glacial erosion intensifies. The enlarging of this open ended concavity creates

650-469: 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. A common feature for all fluvial-erosion cirques

676-587: Was formed by intermittent river flow in the Makhtesh Ramon cutting through layers of limestone and chalk, resulting in cirque walls with a sheer 200 metres (660 ft) drop. The Cirque du Bout du Monde is another such feature, created in karst terraine in the Burgundy region of the department of Côte-d'Or in France . Yet another type of fluvial erosion-formed cirque is found on Réunion island , which includes

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