Two major outlet glaciers in East Greenland have suddenly begun to accelerate and retreat. The speeds of Kangerdlugssuaq and Helheim remained steady during the 1990s despite progressive and substantial thinning, but have abruptly increased within the last two years, more than doubling ice flux to the ocean. Had it been an isolated example, the comparable 1998 speed-up of Jakobshavn Isbræ in West Greenland might have been explained simply by its chance retreat past a pinning point. Now that two further Greenland outlets have exhibited similar behavior, a common process seems likely. A remarkable correspondence in the inter-annual patterns of speed and ice-front variation between Kangerdlugssuaq and Helheim implies a significant sensitivity to regional environmental factors. The period of continued warming and thinning appears to have primed these glaciers for a step-change in dynamics not included in current models. We should expect further Greenland outlet glaciers to follow suit.
Introduction Outlet glaciers in Greenland have been thinning over the 1990s
at a rate that cannot easily be explained by changes in surface mass balance. It has been suggested that part of this thinning must result from dynamic change , and indeed two significant outlet glaciers have been observed to have increased in speed in recent years. Jakobshavn Isbræ in West Greenland began a process of thinning, acceleration and retreat in 1998 and Helheim in East Greenland has recently been reported to have accelerated, also in association with a period of substantial thinning .
Nevertheless, the temporal sparsity of velocity data have made it difficult to explain the nature of the relationships between thinning, acceleration and retreat in these glaciers and Jakobshavn and Helheim remain the only reported observations of significant dynamic change in Greenland despite observed thinning on the majority of measured glaciers. In both of these glaciers the acceleration and retreat has been sudden, despite the progressive nature of warming and thinning over some years. Jakobshavn had a floating tongue and the relationship between thinning, acceleration and retreat was complicated by the probable influence of pinning points beneath it . Helheim, and other glaciers in South East Greenland which have been thinning , are not believed to have floating tongues , but thinning is likely to increase buoyancy near the calving front . The thinning during the 1990s was especially strong in the South East, with up to 10 m yr-1 reported for Kangerdlugssuaq and 2 m yr-1 for Helheim and subsequent measurements show that this thinning rate has since increased .
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http://geography.swan.ac.uk/glaciology/adrian/luckman_GRL_feb06.pdf
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