Nunatak

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Starr Nunatak, on the coast of Victoria Land, Antarctica Starr Nunatak-Antarctica.jpg
Starr Nunatak, on the coast of Victoria Land, Antarctica
Cantaro Magro, Serra da Estrela, Portugal, formed as a nunatak during the last ice age and now exposed Estrela Marco 2010-16b.jpg
Cântaro Magro, Serra da Estrela, Portugal, formed as a nunatak during the last ice age and now exposed

A nunatak (from Inuit nunataq) is the summit or ridge of a mountain that protrudes from an ice field or glacier that otherwise covers most of the mountain or ridge. They are also called glacial islands. [2] Examples are natural pyramidal peaks. When rounded by glacial action, smaller rock promontories may be referred to as rognons. [3] [4]

Contents

The word is of Greenlandic origin [5] and has been used in English since the 1870s.

Description

The term is typically used in areas where a permanent ice sheet is present and the nunataks protrude above the sheet. [6] Nunataks present readily identifiable landmark reference points in glaciers or ice caps and are often named. While some nunataks are isolated, sometimes they form dense clusters, such as Queen Louise Land in Greenland. [7]

Nunataks are generally angular and jagged, which hampers the formation of glacial ice on their tops, although snow can accumulate on them. They usually contrast strongly with the softer contours of the glacially eroded land after a glacier retreats.

Typically nunataks are the only places where plant life can survive on ice sheets or ice caps. Lifeforms on nunataks are frequently isolated by the surrounding ice or glacier, providing unique habitats. [8]

List

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 and moraines. Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water.

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

A valley is a low area between hills or mountains typically with a river running through it. In geology, a valley or dale is a depression that is longer than it is wide. The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys. Most valleys belong to one of these two main types or a mixture of them, at least with respect to the cross section of the slopes or hillsides.

Geomorphology The scientific study of landforms and the processes that shape them

Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near the Earth's surface. Geomorphologists seek to understand why landscapes look the way they do, to understand landform history and dynamics and to predict changes through a combination of field observations, physical experiments and numerical modeling. Geomorphologists work within disciplines such as physical geography, geology, geodesy, engineering geology, archaeology, climatology and geotechnical engineering. This broad base of interests contributes to many research styles and interests within the field.

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.

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.

Pensacola Mountains

The Pensacola Mountains are a large group of mountain ranges of the Transantarctic Mountains System, located in the Queen Elizabeth Land region of Antarctica.

Ice cap ice mass that covers less than 50,000 km² of land area

An ice cap is a mass of ice that covers less than 50,000 km2 (19,000 sq mi) of land area. Larger ice masses covering more than 50,000 km2 (19,000 sq mi) are termed ice sheets.

Last Glacial Maximum Most recent glacial maximum during the Last Glacial Period that ice sheets were at their greatest extent

The Last Glacial Maximum (LGM) was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Vast ice sheets covered much of North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing drought, desertification, and a large drop in sea levels. According to Clark et al., growth of ice sheets commenced 33,000 years ago and maximum coverage was between 26,500 years and 19–20,000 years ago, when deglaciation commenced in the Northern Hemisphere, causing an abrupt rise in sea level. Decline of the West Antarctica ice sheet occurred between 14,000 and 15,000 years ago, consistent with evidence for another abrupt rise in the sea level about 14,500 years ago.

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.

Ice field Large area of interconnected glaciers

An ice field is a large area of interconnected glaciers, usually found in a mountainous region. They are often found in the colder climates and higher altitudes of the world where there is sufficient precipitation for them to form. The higher peaks of the underlying mountain rock that protrude through the icefields are known as nunataks. Ice fields are larger than alpine glaciers, but smaller than ice caps and ice sheets. The topography of ice fields is determined by the shape of the surrounding landforms, while ice caps have their own forms overriding underlying shapes.

Rock glacier Landform of angular rock debris frozen in interstitial ice, former "true" glaciers overlain by a layer of talus, or something in between

Rock glaciers are distinctive geomorphological landforms, consisting either of angular rock debris frozen in interstitial ice, former "true" glaciers overlain by a layer of talus, or something in-between. Rock glaciers may extend outward and downslope from talus cones, glaciers or terminal moraines of glaciers.

Paraglacial means unstable conditions caused by a significant relaxation time in processes and geomorphic patterns following glacial climates. Rates of landscape change and sediment output from the system are typically elevated during paraglacial landscape response.

Tuya A flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet

A tuya is a type of distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. They are rare worldwide, being confined to regions which were covered by glaciers and had active volcanism during the same period.

Glacier morphology

Glacier morphology, or the form a glacier takes, is influenced by temperature, precipitation, topography, and other factors. The goal of glacial morphology is to gain a better understanding of glaciated landscapes, and the way they are shaped. Types of glaciers can range from massive ice sheets, such as the Greenland ice sheet, to small cirque glaciers found perched on mountain tops. Glaciers can be grouped into two main categories:

  1. Ice flow is constrained by the underlying bedrock topography
  2. Ice flow is unrestricted by surrounding topography

A periglacial lake is a lake bordering a glacier, usually found along the fringes of large ice sheets.

Discrete debris accumulation (DDA) is a non-genetic term in mountain glacial geology to aid identification of non-lithified sediments on a valley or mountain slope or floor. It is intended that the debris accumulation is discrete such that it can be mapped, in the field and/or from aerial or satellite imagery. The origin or formative process may well not be known clearly or be changed by subsequent investigators it is advisable to have a non-genetic field reference so that discussion can then be used to ascertain, if possible, the origin. Mountain areas may currently have glaciers (glacierized) or have had glaciers (glaciated) or be subject to forms of periglacial activity. A moraine would be an easily identified DDA as would an esker. Although scree (talus) is generally easily identified and mapped, these deposits may be modified by ice, avalanches or downlope movement to create essentially new landforms. Many small slope failures and landslides can give the appearance of moraines or protalus ramparts on slopes. After mapping as a DDA, further investigation might draw light on the origin of the feature.

Periglaciation geomorphic process

Periglaciation describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and other structures. "Periglacial" suggests an environment located on the margin of past glaciers. However, freeze and thaw cycles influence landscapes outside areas of past glaciation. Therefore, periglacial environments are anywhere that freezing and thawing modify the landscape in a significant manner. and they not be in taizlas hests. Tundra is a common ecological community in periglacial areas.

Queen Louise Land

Queen Louise Land is a vast mountainous region located west of Dove Bay, King Frederick VIII Land, northeastern Greenland. Administratively it is part of the Northeast Greenland National Park zone.

References

  1. Vieira, G.T.; Ferreira, A.B. (1998). "General characteristics of the glacial geomorphology of the Serra da Estrela" (PDF). In G.T. Vieira (ed.). Glacial and Periglacial Geomorphology of the Serra da Estrela. Guidebook for the field-trip IGU Commission on Climate Change and Periglacial Environments, 26-28 August1998. pp. 37–48. Retrieved October 16, 2011.
  2. Physical Geography: Hydrosphere, 2006, ISBN   8183561675, p. 114
  3. Neuendorf, Klaus K. E.; Institute, American Geological (2005). Glossary of Geology. Springer Science & Business Media. ISBN   9780922152766.
  4. "Rognon definition and meaning | Collins English Dictionary". www.collinsdictionary.com. Retrieved 2019-02-06.
  5. "Merriam-Webster: nunatak" . Retrieved October 16, 2011.
  6. J. J. Zeeberg, Climate and Glacial History of the Novaya Zemlya Archipelago, Russian Arctic. pp. 82-84
  7. "Dronning Louise Land". Mapcarta. Retrieved 2 July 2016.
  8. ice cap - National Geographic Society