Glacier-volcano interactions deduced by SAR interferometry

Glacier-surface displacements produced by geothermal and volcanic activity beneath Vatnajokull ice cap in Iceland are described by field surveys of the surface topography combined with interferograms acquired from repeat-pass synthetic aperture radar images. A simple ice-flow model serves well to confirm the basic interpretation of the observations. The observations cover the period October 1996-January 1999 and comprise: (a) the ice-flow field during the infilling of the depressions created by the subglacial Gjalp eruption of October 1996, (b) the extent and displacement of the floating ice cover of the subglacier lakes of Grimsvotn and the Skafta cauldrons, (c) surface displacements above the subglacier pathways of the jokulhlaups from the Gjalp eruption site and the Grimsvotn lake, (d) detection of areas of increased basal sliding due to lubrication by water, and (e) detection of spots of temporal displacement that may be related to altering subglacial volcanic activity. At the depression created by the Gjalp eruption, the maximum surface displacement rate away from the radar decreased from 27 cm d(-1) to 2 cm d(-1) over the period January 1997-January 1999. The observed vertical displacement of the ice cover of Grimsvotn changed from an uplift rate of 50 cm d(-1) to sinking of 48 cm d(-1), and for Skafta cauldrons from 2 cm d(-1) to 25 cm d(-1).