Volcanic blast 'as great a threat to UK security as nuclear terrorism'
AN ERUPTION of a supervolcano in Iceland should pose as great a threat to Britain as nuclear terrorism, according to a high level UK government report.
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“Geologist [I'm Climate Change]”
Since: Mar 07
#1 Apr 28, 2014
Interesting: The report was missing a certain something though.
Iceland is on the junction between the Eurasian, W. Eurasian (France UK Ireland, Iberia,+ Atlantic marine to the mid Atlantic ridge), and N.American plates.
The bit missing is crustal relaxation due to megathrust earthquakes. The result is that for the bulk of the time the entire plate compresses from the subduction zones inward across the plate, resulting most of the time in slow episodic rift spreading @ the ridge, & occasionally long periods of dormancy @ the central volcanoes in Iceland where magma beneath is diverted into the rift zones of adjacent volcanoes.
The result with steady state rifting is series of eruptions of relatively small volume such as @ Eyafjatlajokull, Krafla, Grimsvotn, Hekla etc, when spreading results in a dike series & eruptions where the relatively thin dike reaches the surface. Large volcanoes over the controlling hotspot such as Katla, Grimsvotn & Veidivotn (currently dormant & bypassed by Grimsvotn), will eventually erupt gas rich magma tapped from the disc of magma accumulating @ the base of the volcano producing a plinian column (as in Grimsvotn about 3 years ago whre the column reached 20Km.
Megathrusts relax the crust of the entire plate which deforms like a rubber block. the result is a sudden widening of the rift system @ Iceland & surrounds in a great circle connected to the vector runout of the megathrust. Now the fun & games bit..
The last megathrust in the region was Lisbon in 1755 which relaxed the crust of the W. European plate along both megathrusts of the zygomorph in BOTH NW-SE vector AND NNW-SSE vectors as a result of an initial oblique megathrust in the initial vector followed by crustal relaxation stretching from the Cadiz-Lisbon zygomorph (megathrust both sides), upward to the SE part of the icelandic rift system.
This event not only relaxed the rift, it also reactivated rifting along the SE spur extending from Vestmannaejar through to the Kolbeinsey ridge N. of Krafla stretching through Grimsvotn. The reactivated rift volcanoes are as a result still active right now.
This crustal relaxation opened the rift @ Grimsvotn tapping the deep magma disc & this created the large volume lava eruption @ Lakagigar (Laki) which plated over the area SW. of Vatnajokull with 14Km3 of lava & in the process killed a large number of the icelandic population via Fluorine poisoning & killed a large number of the European population due to low level SO2 smog.
Of major interest is that this event & earlier repetitions also results in the current growth of the Vestmannaejar spur, & the dormancy of the volcanoes in the Reykjavik spur which are still accumulating magma in discs beneath them. A crustal relaxation of the N. American plate in SW. vector @ Cascadia will reactivate that now fairly long dormant part of the rift.
Also for the record, relaxation of the crust of the Eurasian plate has also been responsible for major events @ Iceland. The Aegean arc megathrust event of 1303 appears to have had a minor effect but appears mainly to have hit Jan Mayen island & the kolbeinsey ridge. Also of note the range Megathrust catastrophe which struck the Atlas, Alps, Caucasus, Bojnurd, Pashtun range, NW.Pamir junction & Taklamakan in ~14500BC or thereabouts, relaxed the entire Eurasian plate & W. European plates & completely decompressed Iceland resulting in production of large numbers of Early Holocene shield volcanoes from all over the rift system.
End result is that megathrust events are rather important in producing the big eruptions warned about in the article.
Also important appears to be late stage events caused by re accumulation of magma in discs beneath rifting volcanoes. The ~950AD eruption of Katla (Eldgja) appears to be a late stage event occurring about 1000 years after the last megathrust event @ Lisbon-Cadiz. It may have been the result of a Cascadia megathrust event.
have a nice day: Ag
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