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Blue-ice area
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Blue-ice area
A blue-ice area is an ice-covered area of Antarctica where wind-driven snow transport and sublimation result in net mass loss from the ice surface in the absence of melting, forming a blue surface that contrasts with the more common white Antarctic surface. Such blue-ice areas typically form when the movement of both air and ice are obstructed by topographic obstacles such as mountains that emerge from the ice sheet, generating particular climatic conditions where the net snow accumulation is exceeded by wind-driven sublimation and snow transports.
Only about 1% of Antarctic ice area can be considered to be blue-ice area, but they have attracted scientific interest due to the large numbers of meteorites that accumulate on them; these meteorites either fall directly on the blue-ice area and remain there, or they fall elsewhere into the ice sheet and are transported to the blue-ice area by ice flow. Additionally, ice up to 2.7 million years old has been obtained from blue-ice areas. Blue-ice areas are sometimes used as runways for aircraft.
Blue-ice areas have a generally smooth and often rippled appearance, a blue colour and a sparseness of bubbles in the ice. This light blue colour is a consequence of the absorption of light by ice and air bubbles encased within it, and is the source of the name "blue-ice area". It contrasts markedly with the white colour of Antarctic plains and can be seen from space and from aerial images, while the density of the blue ice makes it appear on radar images as a dark ice form. Scalloped or rippled surfaces have almost regular surface patterns, although wholly smooth blue-ice areas exist as well, and the terrain even of rippled surfaces features very low aerodynamic roughness, perhaps among the lowest of all permanent natural surfaces. This is because most aerodynamic drag is caused by surface anomalies less than a centimetre long, not larger uneven forms. Wave structures form through sublimation.
The occurrence of supraglacial moraines at blue-ice areas has been reported; these form when debris contained within a glacier accumulates at the surface due to melting or sublimation. Small depressions in the ice known as cryoconite holes are common and are formed where rocks got embedded in the ice, but are absent on more mountainous blue-ice areas.
Typical blue-ice areas often feature intense katabatic winds, with average winds reaching 80 kilometres per hour (50 mph) and gusts of up to 200 kilometres per hour (120 mph); such winds can remove and take up large amounts of snow. They are usually warmer than comparable snow-covered areas, sometimes by up to 6 °C (11 °F), which makes them identifiable from brightness temperature imaging. This warming is due to the lower albedo of the blue ice compared to snow, which results in them absorbing more sunlight and warming more. Blue-ice areas also alter the climate above them.
As commonly defined, blue-ice areas display little or no evidence of melting, thus excluding glaciers and frozen lakes in the Antarctic Dry Valleys where sublimation-dominated ice also occurs, but which may be more comparable to the ablation areas of regular glaciers.
Blue-ice areas were first discovered in 1949–1952 by the Norwegian–British–Swedish Antarctic Expedition. They have been identified only in Antarctica, although similar ice patches on Greenland have been reported and blue ice is widespread at glaciers worldwide. Blue-ice areas make up only about 1% of the Antarctic surface ice; however, they are locally common and scattered across the continent, especially in coastal or mountainous areas, but not directly beside the coastline.
They have been found in Dronning Maud Land, the catchment of the Lambert Glacier, the Transantarctic Mountains and Victoria Land. Individual locations in Antarctica include areas of the Allan Hills, the Queen Fabiola Mountains (the Yamato ice field there covers an area of 4,000 square kilometres (1,500 sq mi) and is the largest such structure), Scharffenberg-Botnen and the Sør Rondane Mountains. Their location has been correlated with specific atmospheric pressures, temperatures and a relative humidity of less than 100%.
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Blue-ice area
A blue-ice area is an ice-covered area of Antarctica where wind-driven snow transport and sublimation result in net mass loss from the ice surface in the absence of melting, forming a blue surface that contrasts with the more common white Antarctic surface. Such blue-ice areas typically form when the movement of both air and ice are obstructed by topographic obstacles such as mountains that emerge from the ice sheet, generating particular climatic conditions where the net snow accumulation is exceeded by wind-driven sublimation and snow transports.
Only about 1% of Antarctic ice area can be considered to be blue-ice area, but they have attracted scientific interest due to the large numbers of meteorites that accumulate on them; these meteorites either fall directly on the blue-ice area and remain there, or they fall elsewhere into the ice sheet and are transported to the blue-ice area by ice flow. Additionally, ice up to 2.7 million years old has been obtained from blue-ice areas. Blue-ice areas are sometimes used as runways for aircraft.
Blue-ice areas have a generally smooth and often rippled appearance, a blue colour and a sparseness of bubbles in the ice. This light blue colour is a consequence of the absorption of light by ice and air bubbles encased within it, and is the source of the name "blue-ice area". It contrasts markedly with the white colour of Antarctic plains and can be seen from space and from aerial images, while the density of the blue ice makes it appear on radar images as a dark ice form. Scalloped or rippled surfaces have almost regular surface patterns, although wholly smooth blue-ice areas exist as well, and the terrain even of rippled surfaces features very low aerodynamic roughness, perhaps among the lowest of all permanent natural surfaces. This is because most aerodynamic drag is caused by surface anomalies less than a centimetre long, not larger uneven forms. Wave structures form through sublimation.
The occurrence of supraglacial moraines at blue-ice areas has been reported; these form when debris contained within a glacier accumulates at the surface due to melting or sublimation. Small depressions in the ice known as cryoconite holes are common and are formed where rocks got embedded in the ice, but are absent on more mountainous blue-ice areas.
Typical blue-ice areas often feature intense katabatic winds, with average winds reaching 80 kilometres per hour (50 mph) and gusts of up to 200 kilometres per hour (120 mph); such winds can remove and take up large amounts of snow. They are usually warmer than comparable snow-covered areas, sometimes by up to 6 °C (11 °F), which makes them identifiable from brightness temperature imaging. This warming is due to the lower albedo of the blue ice compared to snow, which results in them absorbing more sunlight and warming more. Blue-ice areas also alter the climate above them.
As commonly defined, blue-ice areas display little or no evidence of melting, thus excluding glaciers and frozen lakes in the Antarctic Dry Valleys where sublimation-dominated ice also occurs, but which may be more comparable to the ablation areas of regular glaciers.
Blue-ice areas were first discovered in 1949–1952 by the Norwegian–British–Swedish Antarctic Expedition. They have been identified only in Antarctica, although similar ice patches on Greenland have been reported and blue ice is widespread at glaciers worldwide. Blue-ice areas make up only about 1% of the Antarctic surface ice; however, they are locally common and scattered across the continent, especially in coastal or mountainous areas, but not directly beside the coastline.
They have been found in Dronning Maud Land, the catchment of the Lambert Glacier, the Transantarctic Mountains and Victoria Land. Individual locations in Antarctica include areas of the Allan Hills, the Queen Fabiola Mountains (the Yamato ice field there covers an area of 4,000 square kilometres (1,500 sq mi) and is the largest such structure), Scharffenberg-Botnen and the Sør Rondane Mountains. Their location has been correlated with specific atmospheric pressures, temperatures and a relative humidity of less than 100%.
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