The effects of basal water beneath Vatnajökull, iceland, on glacier sliding observed from sar interferometry

Eyjólfur Magnússon*, Helmut Rott, Helgi Björnsson, Matthew J. Roberts, Etienne Berthier, Finnur Pálsson

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

We analysed InSAR data from the ERS1/2 tandem mission, obtained within the ERS AO projects VECTRA and A03.239, to study special ice dynamic phenomena on the ice cap Vatnajökull, Iceland. In these data unusually high velocities are observed on Skeioarárjökull, an outlet of Vatnajökull. Three case studies are shown where three dimensional velocities are derived. The first is from late December 1995, during cold and dry weather conditions. The second analysis is from 27-28 March 1996 during a jökulhlaup (glacier outburst) from Grímsvötn which flows into Skeioará, the main glacier river of Skeioarjökull. The effects of the jökulhlaup are clearly observed by 2-3 times faster surface velocities over large areas, compared to the December scene. The water also seems to accumulate at some location in the path of the jökulhlaup below or within the glacier. The observations are made from an interferogram during the early stage of the jökulhlaup when only slight increase had been measured in Skeioará water discharge compared to later stages. Classical jökulhlaup theory describing water flow via a single semi-cylindrical channel, can not alone explain the widespread impact. The second case study is from 23-24 October 1996 where autumn rainfall of medium intensity (∼10 mm/day) seems to trigger the multiple of average movements of Skeioaŕrjökull. The effects of this rainfall are observed as well over large parts of Vatnajökull as both velocity increase and accumulation of water at the glacier basin inferred from vertical motion are observed in the interferogram. An interferogram from a descending orbit on a rainy day two days earlier shows the same on Skeioarárjökull. This along with the fact that measured ice-quakes on Skeioarárjökull, caused by fracture of moving ice, are most frequent during rainfall, suggest high variability in the velocity of temperate glaciers. SPOT 5 images acquired in August and October 2004 also indicate higher average velocity than normally observed in InSAR scenes on Skeioará rjökull. This means that estimating the mass fluxes of temperate glaciers over longer time periods from InSAR data of short time intervals may result in considerable underestimate since most usable image pairs are acquired under dry conditions.

Original languageEnglish
Title of host publicationProceedings of Fringe 2005 Workshop
Edition610
Publication statusPublished - Feb 2006
EventFringe 2005 Workshop - Frascati, Italy
Duration: 28 Nov 20052 Dec 2005

Publication series

NameEuropean Space Agency, (Special Publication) ESA SP
Number610
ISSN (Print)0379-6566

Conference

ConferenceFringe 2005 Workshop
Country/TerritoryItaly
CityFrascati
Period28/11/052/12/05

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