Box 24 Surgetype Glaciers In Svalbard

An estimated 35% of the glaciers on Svalbard are surge-type; that is they are prone to dramatic increases in velocity and rapid frontal advances, followed by periods of quiescence during which velocities are generally low. Surge-type glaciers in Svalbard typically have relatively long quiescent phases (10-200 years) between short-lived surge events (1-5 years). Jiskoot et al. (2000) analysed statistically the possible controls on the distribution of surge-type glaciers in Svalbard using a large number of glacial and geological attributes. They looked at the potential effects of geology, mass-balance conditions and thermal regime on surging. They concluded from their analysis that long polythermal glaciers with relatively steep slopes overlying young fine-grained sedimentary lithologies are most likely to be of surge type in Svalbard. They found no statistical relationship between geology and surge-type behaviour. Possible explanations for the importance of glacier length are transport-distance-related substrate properties, distance-related attenuation of longitudinal stresses and the relationship between glacier size and polythermal glacier regime. The overall conclusion of their study is that the surge-type potential of Svalbard glaciers is greatest for polythermal glaciers overlying fine-grained potentially deformable beds. The photograph over the page shows the snout of a small surging glacier (Arebreen) in Svalbard.

Source: Jiskoot, H., Murray, T. and Boyle, P. (2000) Controls on the distribution of surge-type glaciers in Svalbard. Journal of Glaciology, 46, 412-22. [Photograph: M.R. Bennett]

Figure 2.12 Hummocky moraines in front of a receding glacier in Svalbard, interpreted as the product of englacial thrusting within the ice. [Photograph: N.F. Glasser]

5. Deformation of permafrost is also important in the formation of ice-cored moraines and push moraines (see Section 9.1.1). Stresses beneath the advancing glaciers are transmitted to the proglacial sediments and can be sufficient to cause proglacial deformation of the permafrost layer. Folding, thrust-faulting and overriding of proglacial sediments are also possible under these conditions. The nature of the deformation is controlled by the mechanical properties of the sediment, which is influenced by the water content and thermal condition, whether it is frozen or unfrozen.

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