Abstract
AbstractInterferometric radar images collected by ERS-1, ERS-2 and RADAR- SAT-1 are used to observe the rupture tip of rifts that propagate along Hemmen Ice Rise on the Ronne Ice Shelf, Antarctica. Interferograms generated in 1992 and 1997 allow for the observation of ice deformation accumulated over 9 and 24 days respectively. These interferograms are combined, in order to separate the continuous process of creep deformation from the more cyclic motion caused by variations in ocean tide. An examination of local gradients in creep deformation reveals the pattern of ice deformation around and near the rupture tips and rifts with great precision (up to 10 cm a-1). We compare the observations with a deformation model for ice and obtain the following results: (1) The tidal oscillation of the Ronne Ice Shelf only yields small deformations along the rifts and near the rupture tips. (2) Along the ice front, the rifts and at the rupture tips, vertical bending is observed which is well explained by a model of viscous deformation of ice. Furthermore, the model indicates that the deformation pattern observed at the rupture tips is a sensitive indicator of the propagation state of the rifts (i.e. active vs inactive). (3) The viscous adjustment of ice is the dominant mode of deformation, masking the deformation pattern predicted by linear elastic fracture mechanics (LEFM). (4) Yet, at a spatial scale equivalent to the length of a rift, the propagation rate is well predicted by LEFM.
Highlights
The evolution of ice shelves is controlled by many factors (Jacobs and others, 1992), one of which is the episodic calving of large tabular icebergs
(3) The viscous adjustment of ice is the dominant mode of deformation, masking the deformation pattern predicted by linear elastic fracture mechanics (LEFM). (4) Yet, at a spatial scale equivalent to the length of a rift, the propagation rate is well predicted by LEFM
This study shows that very subtle patterns of deformation are revealed by InSAR along rupture tips of rifts in an ice shelf
Summary
The evolution of ice shelves is controlled by many factors (Jacobs and others, 1992), one of which is the episodic calving of large tabular icebergs. The iceberg detached along a pre-existing line of weakness, namely a rift emanating from HIR This event provides a unique opportunity to study the mechanics of rift propagation because extensive satellite imagery was collected before (and after) the event. Surface crevasses are clearly visible in the radar imagery, but there are probably numerous bottom crevasses (Van derVeen, 1998b) Some of these crevasses develop into rifts, i.e. deep incisions through the entire ice-shelf thickness, which create major lines of weakness in the ice shelf. On 13 October 1998, the rift marked 3 in Figure 1a became unstable and rapidly propagated through the ice shelf, giving birth to tabular iceberg A38 This large calving event was soon followed by a series of other calving events in the same region
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