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22-503: Cwm Idwal is a cirque (or corrie) in the Glyderau range of mountains in northern Snowdonia , the national park in the mountainous region of North Wales . Its main interest is to hill walkers and rock climbers , but it is also of interest to geologists and naturalists, given its combination of altitude (relatively high in UK terms), aspect (north-facing) and terrain (mountainous and rocky). In

44-638: 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

66-457: A 2005 poll conducted by Radio Times , Cwm Idwal was ranked the 7th greatest natural wonder in Britain. Cwm Idwal is a spectacular product of glaciation , surrounded by high crags, screes , moraines and rounded rocks, with a lake on its floor ( Llyn Idwal ). Cwm Idwal comprises volcanic and sedimentary rock which was laid down in a shallow Ordovician sea, and later folded to give rise to

88-487: 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

110-405: Is a terrain which includes erosion resistant upper structures overlying materials which are more easily eroded. Notes Citations Bedrock In geology , bedrock is solid rock that lies under loose material ( regolith ) within the crust of Earth or another terrestrial planet . Bedrock is the solid rock that underlies looser surface material. An exposed portion of bedrock

132-413: 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 a mountainside near the firn line , they are typically partially surrounded on three sides by steep cliffs . The highest cliff

154-506: Is also a home of the Snowdon lily , a plant which can only be found in the UK on Snowdon and its surroundings. Evan Roberts , the renowned botanist and explorer from Capel Curig , did probably as much as any other (self-taught) botanist to document the area. The Snowdonia hawkweed, Hieracium snowdoniense is only known to occur in Cwm Idwal. Rhiwiau Caws (Idwal Slabs) and the cliffs around

176-423: 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 the opening of the bowl and form valley glaciers which may be several kilometers long. Cirques form in conditions which are favorable; in

198-472: Is often called an outcrop . The various kinds of broken and weathered rock material, such as soil and subsoil , that may overlie the bedrock are known as regolith . The surface of the bedrock beneath the soil cover (regolith) is also known as rockhead in engineering geology , and its identification by digging, drilling or geophysical methods is an important task in most civil engineering projects. Superficial deposits can be very thick, such that

220-572: 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

242-459: 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,

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264-433: The bedrock lies hundreds of meters below the surface. Exposed bedrock experiences weathering , which may be physical or chemical, and which alters the structure of the rock to leave it susceptible to erosion . Bedrock may also experience subsurface weathering at its upper boundary, forming saprolite . A geologic map of an area will usually show the distribution of differing bedrock types, rock that would be exposed at

286-451: 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,

308-406: 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

330-587: The distinctive trough-shaped arrangement of strata known today as the Idwal Syncline . This fold in the rock is visible today, thanks to the layering of the sedimentary rocks. The area was then eroded by glacial action to form the classic semicircular valley. Given its elevation and north-facing aspect, Cwm Idwal is the most southerly place in Britain where Arctic plants such as moss campion and some alpine saxifrages , such as tufted saxifrage ( Saxifraga cespitosa ) and Micranthes nivalis , can be found. It

352-465: 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, is formed by intermittent river flow cutting through layers of limestone and chalk leaving sheer cliffs. A common feature for all fluvial -erosion cirques

374-510: The head of Cwm Idwal are a popular area for rock climbing; Rhiwiau Caws (on the eastern side of the Cwm) in particular are popular with inexperienced climbers learning their skills. They were first climbed in 1897 by Rose and Moss. Twll Du has some excellent ice climbing during the winter. The Cwm is also popular for hill walking and scrambling , given its proximity to Tryfan and Glyder Fach and Glyder Fawr and their profusion of rocky ridges. In

396-455: The mid-to-late 1950s and into the 1960s, this was the reunion excursion campsite of the first ascenders of Mount Everest and Kangchenjunga , held at Pen-y-Gwryd , many of whom were keen geologists and botanists . [REDACTED] Cirque 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

418-469: 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

440-429: 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 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,

462-401: 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 a larger leeward deposition zone, furthering the process of glaciation. Debris (or till) in the ice also may abrade

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484-587: 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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