The Grímsvötn area is one of the testsites in the ENVISAT project ID 142 "Hazard Assessment and Prediction - Longterm Observation of Icelandic Volcanoes and Glaciers Using ENVISAT-ASAR and Other Radar Data". Therefore a continuous acquisition of ENVISAT-ASAR data (modes IS 2, IS 5) from the study area is guaranteed.
The overall purpose of the AO Project is the monitoring of changes in glacier and other surfaces caused by geothermal, seismic and volcanic activity in the neovolcanic zone in southern Iceland.

On November, 1st 2004 (ca. 22.00 GMT) an eruption at Grímsvötn caldera - a subglacial volcanic system beneath the western part of Vatnajökull glacier - started, after a dormant phase of only 6 years since its last outbreak in December 1998.
In spite of the usual eruption characteristics a glacial torrent (icl. Jökulhlaup) occured (30.10.2004) before the hot phase and triggered the eruption due to the release of the overburden water pressure.

Due to special arrangement with ESA it is possible now to receive and process ASAR data around 24 hours after acquisition.
The 2004 eruption period is covered by a data sequence with short acquisition intervals. This gives us the unique chance of NRT observation of a subglacial outbreak over the whole eruption period. The scenes dating from 24.10., 31.10., 04.11., 09.11., 11.11., 12.11., 13.11., 27.11. and 28.11.2004 have already been received and fully integrated in our hazard monitoring GIS.

Early recognition of subglacial volcanic processes by radar monitoring (ESA-project AO 2 D 116) was possible during the subglacial volcanic eruption of Gjálp (30.9.-13.10.96) and Grímsvötn (18.-28.12.98) and has now been confirmed as a suitalbe tool by the new eruption (Nov. 2004).
Evaluation of the new ASAR data showed that 8 days ahead of the recent eruption on 24.10.04 the exact position of the eruption site inside the caldera could be located through the glacial ice cover. 35 hours prior to the eruption, on 31.10.04, the extent could be detected in detail.
This indicates at least 8 days before the eruption there has been a magma intrusion under the Grímsvötn caldera with the effect of melting the glacial ice layer from underneath. The meltdown led to the glacial torrent on 30.10.04 which then indirectly triggered the eruption.

Moreover examination of the ASAR data (31.10./04.11./09.11./11.11./12.11. and 13.11.04) show enormous water level changes in lake Graenalón, a water reservoir close to the Skeidarárjökull.

The ENVISAT-ASAR data sequence will be continued.

Last Update : 03.12.04