Wednesday, May 16, 2012

Large Quake Swarm Under Herðubreið in Iceland

A large swarm of earthquakes is occurring just NE of the Askja caldera in Iceland. This began sometime yesterday and continues to the time of this writing (see below pic). It has recently been noted that Askja caldera was strangely ice free during the cold months, with the water still quite cold, yet unfrozen. Some theories about this pointed to possible underwater fumeroles, to chemical changes, and other theories, but as of yet nobody can fully explain why.


Picture graph from Iceland Meteorological Office


The current swarm of earthquakes is most likely related to magma dike intrusion. Currently I am unable to determine the depth of these quakes, but most quake swarms in Iceland are volcanic in nature, given that the entire land of Iceland is basically riding on top of a mantle plume, and is also smack-dab on the middle of a spreading ridge between the North American and European plates which are drifting away from each other.

The swarm's location is actually under a "tuya" named Herðubreið. A tuya is a volcano that most likely formed underneath a glacier, but never pierced the surface to produce an explosive eruption. There are many examples of tuyas in Iceland, Canada, Alaska, and other cold regions of the world where volcanism occurs. Most tuyas were formed during the ice age, as the ice back then was extremely thick and not even a volcanic eruption would have been able to break free of the ice. Herðubreið is theorized to have erupted in the last glacial ice period.

The nearby volcano, Askja, has also seen some recent possible activity (I covered the strange happenings at Askja in a previous post). The last time Askja erupted, according to the Smithsonian GVP, was in 1961 and produced lava flows from a fissure vent system near Öskjuvatn lake. The caldera forming event occurred in 1875, and was one of the largest eruptions seen in historical times by Iceland (with of course the exception of the famed Laki eruption that has been blamed for famine in Europe and the eventual catalyst for the French Revolution). An eruption from Askja today would likely consist of fissure fed lava flows with some minor explosions. The last report on activity at Askja included a satellite photo that seemed to show some very minor ash deposits near a crater on the rim of the lake, which may or may not be the result of an eruption (it could also be that it was ash was blown that direction from another deposit).

It is completely unknown at this time whether Herðubreið is an active volcano, however given the quake swarm, I would suspect that it is not completely dead. As Chaiten volcano, and Nabro volcano both recently proved, volcanoes long thought to be dead can spring back to life without warning. This is more than true in Iceland, so Herðubreið is a volcano that should be monitored in my opinion (and I am quite sure that it is now). There is no way to tell what type of eruption might occur at Herðubreið, but I would suspect that if any eruption occurs, it will be explosive. There are no towns or villages near Herðubreið as it is in one of the more remote and inhospitable locations in Iceland, so the danger level from pyroclastic flow or otherwise is quite low, however its location could pose a nuisance from ash to Europe.


*****UPDATE 5/18/2012*****

The quake swarm under Herðubreið is still ongoing at this time. Approximately 15+ quakes have occurred under the volcano within the last 48 hours.

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