This page contains scientific data and results from the staff of the Institute of Earth Sciences and various collaborators. The data is posted timely to give maximum information on evaluation of an evolving natural catastrophe. Please respect copyright and authorship of the data.
Saturday morning 28 May at 6:30 UTC the volcanic tremor on Grímsfjall (Grímsvötn) rapidly decreased and had disappeared at 7 UTC. Since Thursday the tremor had been intermittent. Today, Monday 30 May, it has been confirmed by the participants of Iceland Glaciological Society's spring expedition that the eruption has ended.
Eruption of Grímsvötn volcano, begins 21 May 2011
The subglacial Grímsvötn volcano, Iceland, began erupting on 21 May 2011, around 18-19 GMT. The eruption was preceded by intensive earthquake activity lasting for about 1 hour. An ‘ash-loaded’ eruption plume rose rapidly up to about 17 km height (estimated 55000 feet from ground based radar, overview flights, and pilot reports). Ash from the lower part of the eruption plume was deflected southwards and from a higher level towards the east. Few hours after the onset of the eruption ash fall began over wide area in the nearest populated areas south of the Vatnajökull ice cap, at a distance of more than 50 km from the eruption site.
Grímsvötn is a basaltic volcano that has the highest eruption frequency of all volcanoes in Iceland. It is located near the centre of the Vatnajökull ice cap, the largest ice cap in Europe. The volcano has a caldera complex, the most recent one hosting the Grímsvötn subglacial caldera lake that is sustained by extensive geothermal activity. The volcano is almost fully ice covered and interaction of magma and meltwater from the ice causes phreatomagmatic explosive activity.
Initial overview flight, with limited visibility, and earthquakes locations suggest an eruption site in the southwestern part of the Grímsvötn caldera. Ice cover there is relatively thin (50-200 m) and meltwater is anticipated to accumulate within the Grímsvötn caldera lake. From there, it may eventually drain in a sudden glacial outburst flood, jökulhlaup, along a subglacial channel and issue from the Skeiðarárjökull outlet glacier.
The height of the initial plume in the present eruption, 17 km, is much higher than in a preceding eruption at Grímsvötn in 2004. Then an eruption produced a plume reaching an estimated height of 6-10 km above vent. The present plume is also higher than recorded in the Eyjafjallajökull eruption in Iceland last year.
A GPS-station on the rim of the Grímsvötn caldera has revealed continuous inflation and expansion of the volcano of few cm per year since the 2004 eruption, interpreted as inflow of magma to a shallow chamber. Another long-term precursor was increase in seismicity over last few months, including some bursts of tremor. Increase in geothermal activity was as well observed in the months leading to the eruption.
London VAAC forecasts air-traffic interruption limited to Iceland and surroundings.
Information contacts: Icelandic Meteorological Office (www.vedur.is), Institute of Earth Sciences and the Nordic Volcanological Centre, University of Iceland (www.earthice.hi.is).
Prepared by: Freysteinn Sigmundsson (firstname.lastname@example.org), Steinunn Jakobsdóttir (email@example.com), Björn Oddsson (firstname.lastname@example.org), Þórdís Högnadóttir (email@example.com), Sigurlaug Hjaltadóttir (firstname.lastname@example.org), Guðrún Larsen (email@example.com), Magnús Tumi Guðmundsson (firstname.lastname@example.org).