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GEOPHISICAL RESEARCH LETTERS, VOL.25, NO. 7, PAGES 1059-1062, APRIL 1, 1998

Effects of Subglacial Geothermal Activity Observed by Satellite Radar Interferometry

Sigurjón Jónsson

Icelandic Geodedic Survey, Laugarvegur 178, 105 Reykjavík, Iceland

Nico Adam

German Aerospace Research Establishment (DLR), 82230 Oberpfaffenhofen, Germany

Helgi Björnsson

Science Institutu, University of Iceland, Dunhagi 3, 107 Iceland

We use one day Synthetic Aperture Radar (ARA) interferograms from data of the Earth Remote Sensing Satellites ERS-1 and ERS-2 to study ice flow and uplift of two surface depressions within the Vatnajökull ice cap, Iceland. The ice cauldrons are created by melting at sublacial geothermal areas. Meltwater accumulates in a reservoir under the cauldrons over 2 to 3 years until it drains in a jökulhlaup under the ice dam surrounding the reservoir. The ice surface in the depressions drops down by several tens of meters during these draining events but rises again, as ice flows into the depressions, until a jökulhlaup occours again. Using SAR interferograms we quantify an uplift rate af about 2 to 18 cm/day within the jökulhlaup cycle varying with the surface slope of the depressions. The uplift rate is high during the first mounths after a jökulhlaup when the cauldron is relativly deep with steep slopes, but the uplift rate decreases as the cauldron is gradually filled. A simple axisymmetric model simulating the ice-flow into one of the depressions describes quantitatively the filling rate of the cauldron and qualitatively the shape of the ice flow field. The best-fit model has an ice flow law parameter A₀ that is about one order of magnitude lower than typically estimated for temperate glaciers.