Friday, April 26, 2013

Puzzling Seismicity at Helka, Iceland

Hekla volcano in Iceland is not known for giving much advance warning, but this time it may be. Scientists in the area have been monitoring the notorious volcano for signs that it may erupt, as it is "overdue" for a show. Hekla is one of Iceland's most active volcanoes, and also one of its most disruptive. Typically this volcano does not give much warning in the way of tremor or earthquakes, indeed the earthquakes seem to precede an eruption only by hours... yet Hekla has been rumbling now for weeks.


Image copyright Icelandic Meteorological Office at http://en.vedur.is

The above photo details tonights seismicity, and while a 1.0 quake in its vicinity may seem benign, this website does not keep a visual record of quakes over 48 hours. As of now there have been dozens along the fissure zone, main volcano, and the NW area seen here in the picture. Volcanoes don't always behave the same way, sometimes their eruption signals can change. Any seismicity and deformation in the Hekla volcanic system can be reason for worry. Previous eruptions came with not a lot of warnings, as is the case with several volcanoes in the region. 

While Eyjafjallajökull created a bit of havoc for the world in 2010, as well as Grimsvötn (Grimsnes), an eruption of Hekla now has the potential to be every bit as bothersome to the Icleandic people. From pyroclastic ash eruptions to fissure fed lava effusion, this volcano is capable of a varying medley of eruptions, and the last time it erupted was in 2000. The volcano has within the last several decades erupted nearly every 10 years, however the volcano has not always done so, so prediction is not possible. 

A list from the Icelandic Meteorological Office at http://en.vedur.is/earthquakes-and-volcanism/articles/nr/1874 details the following Icelandic eruption dates (last two known eruptions in Iceland left in for reference):

2011 Grímsvötn
2010 Eyjafjallajökull
2000 Hekla
1991 Hekla
1981 Hekla
1980 Hekla
1970 Hekla
1947 Hekla
The Smithsonian GVP profile is below:

Volcano types:
    Stratovolcano
    Fissure vents
Summit Elev: 1491 m
Latitude: 63.98°N
Longitude: 19.70°W
One of Iceland's most prominent and active volcanoes, Hekla lies near the southern end of the eastern rift zone. Hekla occupies a rift-transform junction, and has produced basaltic andesites, in contrast to the tholeiitic basalts typical of Icelandic rift zone volcanoes. A 5.5-km-long fissure, Heklugjá, cuts across the 1491-m-high volcano and is often active along its full length during major eruptions. Repeated eruptions along this rift, which is oblique to most rifting structures in the eastern volcanic zone, are responsible for Hekla's elongated ENE-WSW profile. Frequent large silicic explosive eruptions during historical time have deposited tephra throughout Iceland, providing valuable time markers used to date eruptions from other Icelandic volcanoes. Hekla tephras are generally rich in fluorine and are consequently very hazardous to grazing animals. Extensive lava flows from Hekla's historical eruptions, which date back to 1104 AD, cover much of the volcano's flanks.

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