A model for the Horcones Inferior Glacier surge (Aconcagua region, Argentina): Brittle vs. Plastic glacier flow

MILANA, J. P

JOURNAL OF GLACIOLOGY

INT GLACIOL SOC

Lugar: London; Año: 2007 vol. 53 p. 565 - 572

0022-1430

The deformation, resulting from a surge in 1985, of the Horcones Inferior Glacier is analyzed using structural geological models. During the surge, previously continuous debris-cover was deformed by the formation of regularly-separated and rotated ice blocks, suggesting a system of linked rotational extensional faults. Block tilting was measured from photographs taken shortly after the surge, showing rotation of the debris-cover surface. Fault inclination was assumed to be coincident with the debris-free side of the block. Glacier advance during the surge was obtained by comparing pre-surge aerial photographs with the position of maximum advance after the surge. Glacier thinning was estimated from the debris surface average lowering (relief generated at lateral scarps coincident with shear zones) and ice thickness measurements using a portable radar after surge termination. Three independent sets of information, geometry of the deformation (i.e. depth of detachment, fault traces, fault spacing, block rotation), glacier thinning and net advance, limit possible interpretations. Surface geometry suggests a domino-style or a linked planar rotational extensional fault system. In the observed configuration however, only 12 to 13% of the extension can be explained. Glacier thinning suggests 30%  local extension, and total glacier advance implies 16% extension. This needs to include some observed frontal compression. A linked curved rotational extensional fault model fits the data well, implying a significant degree of internal deformation within each block. The model satisfactorily explains the observed deformation produced by the surge. It might also explain some modes of fast glacier flow, since the observed style of block tilting is present in other glaciers with high relief.