Grímsvötn volcano
Status Report: 16:00 GMT, 24 May 2011
Icelandic Meteorological Office and Institute of Earth Sciences, University of Iceland
Compiled by:
Gunnar B. Guðmundsson and Freysteinn Sigmundsson with input
from Elín Björk Jónasdóttir, Árni Sigurðsson, Bergthóra S.
Thorbjarnardóttir, Þórður Arason, Matthew J. Roberts, Gunnar
Sigurðsson, Björn Oddsson, Magnús Tumi Guðmundsson, Ingibjörg
Jónsdóttir and Sigrún Hreinsdóttir.
Based on:
IMO seismic monitoring; IES-IMO GPS monitoring; IMO
hydrological data; weather radar; ashfall reports; UK Met Office
ATDnet; MODIS and NOAA satellite images
Eruption plume:
Height (a.s.l.):
The ash plume was not visible on radar for most of the night and early
this morning due to weather conditions at the eruption site and around
it. The estimated height is below 5 km since clouds over the glacier
were at 5-7 km and the plume did not reach above the cloud deck.
The ash plume reached 8 km briefly at 14 UTC today, but decreased
shortly there after. According to pilot reports the plume is visible at
around 10 thousand feet, mostly light gray or brown in color, but
pulsating to 15 thousand feet, and becoming darker in the process.
Based on plume height, the estimated magma discharge rate equals 10-
70 tonnes/s of ash. A large part of Vatnajökull is covered by clouds
and the eruption plume is not well defined in satellite images. South of
Iceland images show visible ash extending over 800 km from the
eruption site towards the south and southeast.
Heading:
A large part of the ash heads to the south.
Colour:
Mostly light gray.
Tephra fallout:
The axis of the main tephra sector has a direction S - SSW from
Grímsvötn. Ash clouds is mainly confined between Lomagnupur and
Myrdalsjökull. It is not very thick and it is mixed with blowing ash. In
Kirkjubaejarklaustur the ashfall has decreased compared to yesterday.
The visibility this morning was around 200 m but around noon only
100 m and the sky became dark.
Lightning:
No lighning strikes have been detected since yesterday afternoon.
Noise:
No noise from the volcano has been reported.
Meltwater:
There is no sign of flooding in the rivers Gígjukvísl or Núpsvötn,
which drain from the Skeiðarárjökull glacier. As the eruption is
occurring at the same location as the 2004 eruption, little ice is
available for melting. A large outburst flood (jökulhlaup) is unlikely,
assuming that the eruption remains in the same location. The electrical
conductivity of Núpsvötn has continued to increase; this is due to ash-
fall on the western side of Skeiðarárjökull. Conductivity levels in
Gígjukvísl remain unchanged.
Conditions at eruption site: The eruption site is in the southwest corner of the
Grímsvötn caldera. Weather conditions have prevented overview
flights since yesterday. The eruption has not yet been visited on
ground.
Seismic tremor:
Seismic tremor at the Grímsfjall station has been fairly stable since
yesterday afternoon but some fluctuations are observed.
Earthquakes:
No earthquakes were recorded in the volcano today. Three earthquakes
or possible icequakes occurred about 12-20 km south of the volcano
yesterday evening.
GPS deformation:
The GPS-station at Mt. Grimsfjall showed insignificant displacements
from 00:00 - 24:00 yesterday.
Overall assessment: Based on the development of plume height, ash fall in inhabited areas
in Iceland, number of lightning strikes, seismic tremor and ground
deformation, it is inferred that the strength of the eruption continues to
decline, with present explosive activity only a small fraction of its
initial values.
Details in
status report issued collectively by the Icelandic Meteorological Office and the Institute of Earth Sciences
