Arête

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Striding Edge, an arete viewed from Helvellyn with the corrie Red Tarn to the left and Nethermost Cove to the right Striding Edge.jpg
Striding Edge, an arête viewed from Helvellyn with the corrie Red Tarn to the left and Nethermost Cove to the right

An arête is a narrow ridge of rock which separates two valleys. It is typically formed when two glaciers erode parallel U-shaped valleys. Arêtes can also form when two glacial cirques erode headwards towards one another, although frequently this results in a saddle-shaped pass, called a col. [1] The edge is then sharpened by freeze-thaw weathering, and the slope on either side of the arête steepened through mass wasting events and the erosion of exposed, unstable rock. [2] The word ‘arête’ is actually French for edge or ridge; similar features in the Alps are often described with the German equivalent term Grat.

Contents

Where three or more cirques meet, a pyramidal peak is created.

Cleaver

Clouds Rest in Yosemite National Park is an arete. Clouds Rest with Half Dome in the background.jpg
Clouds Rest in Yosemite National Park is an arête.

A cleaver is a type of arête that separates a unified flow of glacial ice from its uphill side into two glaciers flanking, and flowing parallel to, the ridge. Cleaver gets its name from the way it resembles a meat cleaver slicing meat into two parts. A cleaver may be thought of as analogous to an island in a river. A common situation has the two flanking glaciers melting to their respective ends before their courses can bring them back together; the exceedingly rare analogy is a situation of the two branches of a river drying up, before the downstream tip of the island, by evaporation or absorption into the ground.

The location of a cleaver is often an important factor in the choice among routes for glacier flow. For example, following a cleaver up or down a mountain may avoid travelling on or under an unstable glacial, snow, or rock area. This is usually the case on those summer routes to the summit whose lower portions are on the south face of Mount Rainier: climbers traverse the ‘flats’ of Ingraham Glacier, but ascend Disappointment Cleaver and follow its ridgeline rather than ascending the headwall either of that glacier or (on the other side of the cleaver) of Emmons Glacier.

Examples

Crib Goch, Snowdonia, is an arete. Crib Goch, Snowdonia, Wales - August 2007.jpg
Crib Goch, Snowdonia, is an arête.
The Garden Wall, an arete in Glacier National Park Garden Wall.jpg
The Garden Wall, an arête in Glacier National Park

Notable examples of arêtes include:

See also

Related Research Articles

Glacier Persistent body of ice that is moving under its own weight

A glacier is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. Glaciers slowly deform and flow under stresses induced by their weight, creating crevasses, seracs, and other distinguishing features. They also abrade rock and debris from their substrate to create landforms such as cirques, moraines, or fjords. Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that forms on the surface of bodies of water.

Valley Low area between hills, often with a river running through it

A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over a very long period of time. Some valleys are formed through erosion by glacial ice. These glaciers may remain present in valleys in high mountain or polar areas. At lower latitudes and altitudes, these glacially-formed valleys may have been created or enlarged during ice ages but now are ice-free and occupied by streams or rivers. In desert areas, valleys may be entirely dry or carry a watercourse only rarely. In areas of limestone bedrock, dry valleys may also result from drainage taking place underground rather than at the surface. Rift valleys arise principally from earth movements, rather than erosion. Many different types of valley are described by geographers, using terms that may be global in use or else applied only locally.

Moraine Glacially formed accumulation of unconsolidated debris

A moraine is any accumulation of unconsolidated debris, sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice sheet. It may consist of partly rounded particles ranging in size from boulders down to gravel and sand, in a groundmass of finely-divided clayey material sometimes called glacial flour. Lateral moraines are those formed at the side of the ice flow, and terminal moraines were formed at the foot, marking the maximum advance of the glacier. Other types of moraine include ground moraines and medial moraines.

Glaciology Scientific study of ice and natural phenomena involving ice

Glaciology is the scientific study of glaciers, or more generally ice and natural phenomena that involve ice.

Landforms are categorized by characteristic physical attributes such as their creating process, shape, elevation, slope, orientation, rock exposure, and soil type.

Geology of the Yosemite area

The exposed geology of the Yosemite area includes primarily granitic rocks with some older metamorphic rock. The first rocks were laid down in Precambrian times, when the area around Yosemite National Park was on the edge of a very young North American continent. The sediment that formed the area first settled in the waters of a shallow sea, and compressive forces from a subduction zone in the mid-Paleozoic fused the seabed rocks and sediments, appending them to the continent. Heat generated from the subduction created island arcs of volcanoes that were also thrust into the area of the park. In time, the igneous and sedimentary rocks of the area were later heavily metamorphosed.

Tarn (lake) Mountain lake or pool in a glacial cirque

A tarn is a proglacial mountain lake, pond or pool, formed in a cirque excavated by a glacier. A moraine may form a natural dam below a tarn.

Pyramidal peak Angular, sharply pointed mountainous peak

A pyramidal peak, sometimes called a glacial horn in extreme cases, is an angular, sharply pointed mountain peak which results from the cirque erosion due to multiple glaciers diverging from a central point. Pyramidal peaks are often examples of nunataks.

Pirin

The Pirin Mountains are a mountain range in southwestern Bulgaria, with Vihren at an altitude of 2,914 m being the highest peak. One hypothesis is the mountain was named after Perun, the highest god of the Slavic pantheon and the god of thunder and lightning. Another version is that the etymology of the range derives from the Thracian word Perinthos, meaning "Rocky Mountain".

Pirin National Park National park in Bulgaria

Pirin National Park, originally named Vihren National Park, encompasses the larger part of the Pirin Mountains in southwestern Bulgaria, spanning an area of 403.56 km2 (155.82 sq mi). It is one of the three national parks in the country, the others being Rila National Park and Central Balkan National Park. The park was established in 1962 and its territory was expanded several times since then. Pirin National Park was declared a UNESCO World Heritage Site in 1983. The altitude varies from 950 m to 2,914 m at Vihren, Bulgaria's second highest summit and the Balkans' third.

Cirque An amphitheatre-like valley formed by glacial erosion

A cirque is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie and cwm. A cirque may also be a similarly shaped landform arising from fluvial erosion.

Glacial landform Landform created by the action of glaciers

Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have extensive occurrences of glacial landforms; other areas, such as the Sahara, display rare and very old fossil glacial landforms.

Glacial lake Lake formed by a melted glacier

A glacial lake is a body of water with origins from glacier activity. They are formed when a glacier erodes the land, and then melts, filling the depression created by the glacier.

Mount Lyell (California)

Mount Lyell is the highest point in Yosemite National Park, at 13,114 feet (3,997 m). It is located at the southeast end of the Cathedral Range, 1.2 miles (1.9 km) northwest of Rodgers Peak. The peak as well as nearby Lyell Canyon is named after Charles Lyell, a well-known 19th century geologist. The peak had one of the last remaining glaciers in Yosemite, Lyell Glacier. The Lyell Glacier is currently considered to be a permanent ice field, not a living glacier. Mount Lyell divides the Tuolumne River watershed to the north, the Merced to the west, and the Rush Creek drainage in the Mono Lake Basin to the southeast.

Vihren

Vihren is the highest peak of Bulgaria's Pirin Mountains. Reaching 2,914 metres (9,560 ft), it is Bulgaria's second and the Balkans' third highest, after Musala and Mount Olympus. Although due to the karst topography Vihren is deprived of lakes and streams, a number of Pirin's lakes are located around the peak, as is Europe's southernmost glacial mass, the Snezhnika glacielet. Until 1942 Vihren was known as Eltepe ; it was also called Buren (stormy) and Malnienosets (lightning-bringer). The UNESCO World Heritage Site Pirin National Park was originally known as the Vihren National Park. Vihren is included in the 100 Tourist Sites of Bulgaria under No. 2.

Paternoster lake

A paternoster lake is one of a series of glacial lakes connected by a single stream or a braided stream system. The name comes from the word Paternoster, another name for the Lord's Prayer derived from the Latin words for the prayer's opening words, "Our Father"; Paternoster lakes are so called because of their resemblance to rosary beads, with alternating prayer beads connected by a string or fine chain.

Black Buttes

The Black Buttes, also known historically as the Sawtooth Rocks, make up an extinct stratovolcano in the Cascade Volcanic Arc in Whatcom County, Washington, United States. Glacially eroded remnants of this volcano rise above the Deming Glacier, part of the glacier system of the nearby volcano Mount Baker. There are three major peaks — Colfax, Lincoln, and Seward — which can all be climbed.

Malak Polezhan

Malak Polezhan is a peak in the northern section of the Pirin mountain range, south-western Bulgaria. Its height is 2,822 m which places it among the top ten summits of Pirin. The peak is built up of granite. Malak Polezhan is situated on the Polezhan side-ward ridge of the range between the peaks of Polezhan (2,851 m) to the north-east and Dzhengal (2,730 m) to the south.

Southernmost glacial mass in Europe

The southernmost persistent glacial masses in Europe are mainly small glaciers, glacierets, and perennial firn fields and patches, located in the highest mountains of the three big southern European peninsulas - the Balkan, the Apennine, and the Iberian, the southernmost ranges of the Alps and the glaciers on the european northwestern slopes of the Greater Caucasus mountains in Russia. There are summer lasting snow patches in Sierra Nevada, in Mount Olympus (40°05′08″), in Mount Korab (41°47′28″), in Rila Mountain, in Picos de Europa (43°11′51″) in the Cantabrian Mountains, in Mount Maglić (43°16′52″) and others. However, none of them have both persistency and indications of dynamic motion. In southern direction, some 4000 km away, are the glaciers in Africa in Rwenzori Mountains (00°23′09″N), Mount Kenya (00°09′03″S) and Mount Kilimanjaro (03°04′33″S).

Kuklite

Kuklite is a 2,686 m-high peak in the Pirin mountain range, south-western Bulgaria. It is located in the northern part of Pirin on the Kamenitsa secondary ridge between the summits of Yalovarnika (2,763 m), Zabat (2,688 m) to the north-east and Golena (2,633 m) to the south. It is built up of granite. The western and north-western slopes of Kuklite are very steep and are open to the pebbly Begovitsa cirque; the foothills contain accumulations of moraines, densely covered in mountain pine at places. The eastern and south-eastern slopes facing the Bashmandra cirque are grassy and oblique. The Begovishko glacial lake is situated at the northern foothills of the summit.

References

  1. BBC bitesize
  2. Orlove, Ben. "Glacier Retreat: Reviewing the Limits of Human Adaptation to Climate Change". Environment Magazine. Retrieved 30 September 2011.