Surge (glaciology)

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False color image of the Susitna Glacier in Alaska in August 2009. The folded central moraines show that the tributary glacier flowing into the center of the image (coming from the top right), which hardly shows any surge behavior, drives a wedge into the main stream, which is in a resting phase . This had practically cut off the northwest branch during its surge in the years 1951 to 1952, which can be recognized by the separated "drop" in the lower (left) glacier area.

A surge ( English [ sɜːd͡ʒ ] literally for wave) is a typically periodic increase in the flow speed of a glacier . Glaciers where it occurs are called surge glaciers (also known as galloping glaciers). In such glaciers, long periods of normal, slow flow are followed by shorter phases in which they flow 10 to 1000 times faster. The quiescent phase can last decades or centuries, the active phase (surge phase) typically lasts from one to fifteen years. During a surge, considerable amounts of ice are shifted from the nutrient zone to the lower areas of the glacier; the end of the glacier can also advance considerably, but does not have to. There are regional clusters of surge glaciers, especially in Alaska and the northwest of Canada , Iceland , Svalbard and the Pamirs . On average worldwide, surges occur in less than one percent of glaciers. A very noticeable feature of surge glaciers is the appearance of folded central moraines , which form when the main arm or tributary glacier of a glacier system show different surge behavior.

The fastest precisely measured speed during a surge was recorded in 1963 at Brúarjökull in Iceland at 125 meters per day. "The world's fastest glacier" is often known as Kutiah Glacier in the Karakoram called the 12-kilometer should have come during a surge from March to June of 1953, about as average speed 113 meters per day are thereby given. The most spectacular information comes from the Yengutz Har Glacier , also in the Karakoram , which is said to have covered 3.2 kilometers in eight days during its surge that began in 1902.

Geographical distribution

One percent of the world's glaciers are classified as surge glaciers, although advances in remote sensing mean that glaciers are added almost every year. Surges occur across a wide range of glacier types and sizes. It cannot be overlooked, however, that the geographical distribution is not even, with clusters occurring at both global and regional level. In large areas there are no surge glaciers at all, especially many in Alaska , the Yukon Territory , the central Andes , the Tian Shan , the Pamir , Kamchatka , the Karakoram , Iceland , Svalbard , in the Canadian and Russian high Arctic and on Edge of the Greenland Ice Sheet . The catastrophic advances of the Vernagtferner in the Ötztal Alps between the end of the 16th and the beginning of the 20th century are mostly classified as surge behavior, but today there is no such glacier in the Alps anymore.

Possible causes

It has now been established that there must be more than one cause for this phenomenon. Two clearly different types of surge glaciers were identified: the Alaska type (Alaskan type) with a very sudden transition between resting and active phases and the Spitzbergen type (Svalbard type) with more continuous transitions, longer phase duration and significantly shorter ones Flow velocities. The Alaska type are tempered glaciers and it is assumed that the phase transition is caused by a sudden change in the subglacial runoff system in connection with the debris deposits on the glacier floor. In the case of the Spitzbergen type, a thermal cause is assumed which leads to the destabilization of the rubble-infused glacier bed of a polythermal glacier . The Variegated glacier is the prototype of the Alaska type , the counterpart of the Spitzbergen type is the Monacobreen .

literature

  • Hester Jiskoot: Glacier Surging. In: Vijay P. Singh, Pratap Singh, Umesh K. Haritashya (Eds.): Encyclopedia of Snow, Ice and Glaciers. Springer, Dordrecht 2011, pp. 415-428, ISBN 978-90-481-2641-5
  • William D. Harrison, Austin S. Post: How much do we really know about glacier surging? In: Annals of Glaciology. Vol. 36, 2003, pp. 1–6 ( online ; PDF file; 272 kB)
  • Tavi Murray, Tazio Strozzi, Adrian Luckman, Hester Jiskoot, Panos Christakos: Is there a single surge mechanism? Contrasts in dynamics between glacier surges in Svalbard and other regions. In: Journal of Geophysical Research. Vol. 108, 2003, p. 2237 ( doi : 10.1029 / 2002JB001906 )
  • Charles F. Raymond: How do glaciers surge? A review. In: Journal of Geophysical Research. Vol. 92, 1987, pp. 9121-9134 ( doi : 10.1029 / JB092iB09p09121 )

Individual evidence

  1. ^ Hester Jiskoot, Tavi Murray, Paul Boyle: Controls on the distribution of surge-type glaciers in Svalbard. In: Journal of Glaciology. Vol. 46, 2000, pp. 412-422 ( online ; PDF file; 346 kB)
  2. ↑ a b c d H. Jiskoot: Glacier Surging. See literature
  3. ↑ Copland et al .: Expanded and Recently Increased Glacier Surging in the Karakoram. In: Arctic, Antarctic, and Alpine Research. Vol. 43, 2011, pp. 503-516 ( online ; PDF file; 2.77 MB)