The official report from the Grimsvotn volcano, 3 nov 2010:
Grímsvötn volcano
Status Report: 17:00 GMT, 3 November 2010
Icelandic Meteorological Office and Institute of Earth Sciences, University of Iceland
Compiled by: Thorunn Skaftadottir, Egill Axelsson, Steinunn S. Jakobsdottir,
Matthew J. Roberts and Eyjólfur Magnússon
Based on: IMO seismic monitoring; IES-IMO GPS monitoring; IMO
hydrological data; aerial observations from the Icelandic Coastguard
(TF-SIF).
Meltwater: Water continues to drain from Grímsvötn. At 09:30 GMT today,
discharge was gauged at 2,600 m3/s on the Gígja river. Electrical
conductivity has increased to 560 μS/cm. Conductively levels in the
Súla river are similar, indicating that a small volume of geothermal
water is draining from the western side of the Skeiðarárjökull glacier.
It is likely that the jökulhlaup is either at, or nearing, maximum
discharge.
Seismic tremor: At 02:30 GMT today, tremor levels at seismic station 'grf' increased
considerably, particularly in the 1.5 – 5 Hz frequency band. Since then,
tremor levels at grf have remained elevated. A likely cause for the
intensification is a change in drainage rate from Grímsvötn. There is no
sign of low frequency tremor indicative of volcanic activity.
Earthquakes: At 17:44 GMT yesterday, a magnitude 1.6 earthquake was recorded
beneath Grímsvötn. Several micro-earthquakes were detected at grf
during the onset of heightened tremor at 02:30 GMT; these events were
local to grf and probably sourced from the ice. Between 09:03 and
10:45 GMT four tectonic earthquakes were detected beneath
Grímsvötn.
GPS deformation: No change; see status report from 01 November 2010.
Overall assessment: Seismic tremor at Grímsvötn has continued to amplify, indicating
enhanced drainage of water from the subglacial lake. Aerial
observations over Grímsvötn revealed no signs of volcanic activity.
Discharge continued to increase in the Gígjukvísl river, although it is
likely that the jökulhlaup is at, or nearing, maximum discharge.
Presently, there are no detectable signs of the beginning of a volcanic
eruption at Grimsvötn.
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