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Glacial surges are short-lived events where a glacier can advance substantially, moving at velocities up to 100 times faster than normal. Surging glaciers cluster around a few areas. High concentrations of surging glaciers occur in Svalbard, the Canadian Arctic islands, Alaska and Iceland. In some glaciers, surges can occur in fairly regular cycles, with 15 to 100 or more surge events per year. In other glaciers, surging remains unpredictable.〔Summerfield, Michael A., 1991, ''Global Geomorphology, an introduction to the study of landforms,'' Pearson, Prentice Hall. Harlow, England〕 In some glaciers, however, the period of stagnation and build-up between two surges typically lasts 10 to 200 years and is called the quiescent phase.〔 Dowdeswell, J. A., B. Unwin, A. M. Nuttall and D. J. Wingham. 1999. Velocity structure, flow instability and mass flux on a large Arctic ice cap from satellite radar interferometry. Elsevier Science B.V. 〕 During this period the velocities of the glacier are significantly lower, and the glaciers can retreat substantially. ==Types of glacier surges== Glacier surges have been divided into two categories depending on the character of the surge event. Glaciers in Alaska exhibit surges with a sudden onset, extremely high (tens of meters/day)maximum flow rate and a sudden termination, often with a discharge of stored water. These are called Alaskan-type surges and it is suspected that these surges are hydrologically controlled.〔Sharp, M., 1988, ''Surging glaciers: geomorphic effects,'' Progress in Physical geography, http://ppg.sagepub.com〕 Surges in Svalbard typically exhibit different behavior. Svalbard surges are typically associated with slower onset with an acceleration phase, rising to a maximum velocity which is typically slower (up to four or five meters per day) than Alaskan surges, and a return to quiessence often taking years.〔Jiskoot, H. and D. T. Juhlin, 2009, ''Surge of a small East Greenland glacier, 2001–2007, suggests Svalbard-type surge mechanism,'' Journal of Glaciology, Vol. 55, No. 191, pp. 567–570〕〔Murray, T., T. Strozzi, A. Luckman, H. Jiskoot, and P. Christakos (2003), ''Is there a single surge mechanism? Contrasts in dynamics between glacier surges in Svalbard and other regions,'' J. Geophys. Res., 108(B5), 2237, 〕 Features observed during the active or surge phase include potholes, known as lacunas 〔Post, A. 1969, ''Distribution of surging glaciers in western North America,'' J. Glaciol., 8(53), 229-240.〕 and medial moraines.〔Benn, Douglas I. and David J. A. Evans, ''Glaciers and Glaciation,'' Hodder Arnold, 1997 ISBN 978-0-340-58431-6 (verification and page number needed)〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Surge (glacier)」の詳細全文を読む スポンサード リンク
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