Sunday, 7 September 2014

Magnitude 5.4 Earthquake beneath the Vatnajökull Glacier, Iceland.

The Icelandic Met Office recorded a Magnitude 5.4 Earthquake at a depth of 3.9 km beneath the Vatnajökull Glacier slightly before 7.10 am local time (which is GMT) on Sunday 7 September 2014. This was roughly 4 km to the southeast of the Bárðarbunga Volcano, which has been going through an active period for the last month. Magnitude 5.4 Earthquakes are potentially quite dangerous, but the remote location of this event makes it highly unlikely that there were any casualties or damage.

The approximate location of the 7 September 2014 Vatnajökull Earthquake. Google Maps.

Seismic activity beneath volcanoes can be significant, as they are often caused by the arrival of fresh magma, which may indicate that a volcano is about to undergo an eruptive episode. Bárðarbunga last erupted in about 1862, and has undergone several periods of raised seismic activity since then, most recently in 1996 and 2010, so there is no reason to believe that this weeks events will automatically lead to an eruption from the volcano itself. Bárðarbunga began to undergo seismic activity (Earthquakes) on 19 August, and lava began to erupt from a fissure in the Holuhraun lava field, no the north of the Vatnajökull Glacier, late in the evening of Thursday 28 August, and has continued since then. It is though likely that a magma intrusion has risen through fissures beneath the volcano and now migrated to the lava field.

Lava erupting in the Holuhraun lava field in September 2014. Armann Hoskuldsson/Extreme Iceland.

Iceland lies directly upon the Mid-Atlantic Ridge, a chain of (mostly) submerged volcanoes running the length of the Atlantic Ocean along which the ocean is splitting apart, with new material forming at the fringes of the North American and European Plates beneath the sea (or, in Iceland, above it). The Atlantic is spreading at an average rate of 25 mm per year, with new seafloor being produced along the rift volcanically, i.e. by basaltic magma erupting from below. The ridge itself takes the form of a chain of volcanic mountains running the length of the ocean, fed by the upwelling of magma beneath the diverging plates. In places this produces volcanic activity above the waves, in the Azores, on Iceland and on Jan Mayen Island.

The passage of the Mid-Atlantic Ridge beneath Iceland. NOAA National Geophysical Data Center.

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