Arctic Archipelago

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surging glaciers Surging, or surge-type, glaciers are those that undergo periodic phases of rapid flow, punctuating longer intervals of stagnation. Fast flow may last from a few months to a few years, and the inactive phase from between about 20 and 200 years. Velocities at the ice surface can reach up to 50m day⁻¹ during a surge, and the ice becomes heavily crevassed (Fig. 1). These high velocities are often associated with rapid advance of the glacier terminus. One glacier in Svalbard, the island archipelago north of Norway, advanced by 20 km along a 30 km-wide front in less than 2 years, thus earning the name Bråsvellbreen, that is, rapid-growth glacier. Large amounts of ice are transferred from an upper or ‘reservoir’ area to a lower or ‘receiving’ area during surges (see glaciers and glaciology).

The high velocities recorded during the active phase of the surge cycle are linked to the presence of lubricating water at the glacier bed. It is clear from investigations of the subglacial hydrology of surging glaciers that reorganization of this drainage system controls the onset and termination of rapid flow. At Variegated Glacier in Alaska, for example, little melt-water escapes from the glacier during a surge, whereas the rapid shift to low velocities at the termination of a surge is linked closely with the draining of large quantities of sediment-rich water from the glacier.

Only a few per cent of all glaciers are known to surge, and the geographical distribution of surge-type glaciers is remarkably non-random. For example, Alaska, the Yukon, Iceland, the Russian Pamirs, and Svalbard all contain relatively large numbers of surging glaciers, whereas there are very few in the Russian and Canadian Arctic archipelagos. No surges have been observed in Antarctica. Both small and large glaciers surge, including ice-cap outlet glaciers of over 1000 km² in area. Glaciers which have undergone surges in historical times, and at which no direct observations of the active phase have been made, are identified by characteristic series of looped medial moraines on the ice surface, which can easily be recognized from aerial photographs and satellite images.

Surges of glaciers ending in fjords can pose a significant natural hazard. Not only do they calve large numbers of icebergs into the fjord waters during the active phase, making navigation hazardous, but they may also advance across fjords to form a glacier dam. Water levels rise and flooding may follow, together with a shift towards less saline water with potentially disastrous consequences for local marine life.

Julian A. Dowdeswell

Bibliography

Dowdeswell, J. A.,, Hamilton, G. S.,, and and Hagen, J. O. (1991) The duration of the active phase on surge-type glaciers: contrasts between Svalbard and other regions. Journal of Glaciology, 37, 388–400.

Pacific Ocean Largest and deepest ocean in the world, covering c.33% of the Earth's surface and containing more than 50% of the Earth's seawater. The Pacific extends from the Arctic Circle to Antarctica, and from North and South America in the e to Asia and Australia in the w. The e Pacific region is connected with the Cordilleran mountain chain, and there is a narrow continental margin. The ocean is ringed by numerous volcanoes, known as the Pacific ‘Ring of Fire’. There are a number of large islands in the Pacific, most of which are in the s and w. The major ones are New Zealand, and the Japan and Malay archipelagos. The principal rivers that drain into the ocean are the Columbia in North America, and the Huang He and Yangtze in Asia. The average depth of the Pacific is 4300m (14,000ft). The greatest-known depth is that of the Challenger Deep (sw of Guam in the Mariana Trench), which has a depth of 11,033m (36,198ft). The current pattern of the Pacific is made up of two gyres: n of the Equator are the North Equatorial Current, the Kuroshio Current, the North Pacific Drift and the California Current; s of the Equator are the South Equatorial Current, the East Australian Current and the Humboldt Current. The Equatorial Counter-Current separates the two gyres. Most fishing in the Pacific is done on the continental margins. Crab, herring, cod, sardine and tuna are the principal catch. Area: c.166,000,000sq km (64,000,000sq mi).

Arctic Archipelago , group of more than 50 large islands, Northwest Territories and Nunavut, N Canada, in the Arctic Ocean. The southernmost members of the group include Baffin (the archipelago's largest island), Victoria, Banks, Prince of Wales, and Somerset islands; N of Viscount Melville and Lancaster sounds are the Queen Elizabeth Islands, of which Ellesmere is the largest. Tundra and permanent ice cover the islands, on which oil and coal have been discovered. After Greenland, the Archipelago is the world's largest high-arctic land area.