Modelling of the extensional deformation caused by the catastrophic advance (surge) of the lower Horcones Glacier, Mendoza

Abstract

The 1985 lower Horcones Glacier surge offers a unique opportunity to study the deformation mechanisms involved in this surge. This is possible because the glacier had a continuous debris cover over its top, previous to the surge-driven deformation. After the surge, the glacier surface was characterised by evenly separated and equally rotated blocks, pointing to a possible domino-like fault system. The inclination of the limiting faults and the block rotation, were used to estimate glacier stretching under a domino system. Besites, values of glacier-front advance and glacier thinning offer two other ways to control roughly the extension of the system. All these data suggest that a domino system was considered insufficient to explain the minimum amount of stretching observed. Instead, the deformation has been interpreted as being caused by a system of linked planar rotational extensional faults, using a model that explains equally rotated blocks by applying an important amount of internal shear within each block. The deformation of a glacier in relation to a fault system linked to a basal detachment explains the fast advance of the glacier and provides a reasonable explanation for the origin of this event, which was a gravitational collapse produced by an unbalanced accumulation in the up-glacier area with respect to the normal glacier flow. This model explains the initiation of the collapse but does not explain the fast basal sliding. This instead, is interpreted as being related to a phenomenon comparable to a linked-cavity system or a high-pore pressure due to the possibility that this glacier slides over a soft-bed.