Readers may recall that the Grímsvötn volcano caused quite an overwrought mess with air travel in 2011 when it erupted. FergalR writes in WUWT Tips and Notes about the nearby Bárðarbunga volcano becoming seismically active:
A large sub-glacial volcano in Iceland – Bárðarbunga – has been having a huge earthquake swarm for the last 24 hours.
The IMO have just raised the eruption alert level on it.
From the Icelandic Met Office:
Activity in Bárdarbunga volcano
Seismic activity in Bárðarbunga volcano has increased. A seismic swarm has been ongoing since 03AM this morning, and near continuous earthquakes have been occurring since then. The depths of earthquakes in the present swarm are in the upper crust and their magnitudes are mainly around 1.5; a few earthquakes are of magnitude greater than ML3.
Long-term seismic and GPS data indicate that there is increased unrest in the northwestern region of Vatnajökull glacier, where Bárðarbunga is located:
Over the last seven years seismic activity has been gradually increasing in Bárðarbunga and the fissure swarm north of the volcano. This activity dropped down at the Grímsvötn eruption in May 2011, but soon after, the activity started to gradually increase again and has now reached similar level of activity to that just before the Grímsvötn eruption. Earlier this year, in the middle of May 2014, there was a small swarm of over 200 events and now the present swarm has already generated at least 300 earthquakes.
Since early June 2014, displacements at GPS stations around Vatnajökull (Hamarinn, Grímsfjall, Vonarskarð and Dyngjuháls) show an increased upward movement and away from Bárðarbunga.
Together, these two systems indicate magma movements in Bárðarbunga. Due to increased seismicity IMO has decided to turn volcano Barðarbunga status to yellow. In case of a sub-aerial eruption, an ash plume of potential concerns for aviation will be generated. The updated map is available at the link: http://en.vedur.is/weather/aviation/volcanic-hazards/
At 23:00 on August 16, there is no unequivocal indication that magma has reached the surface.