Icelandic Bárðarbunga volcanic eruption begins

These folks are running forecasts for where the plume of ash goes if it honks.
WSI Aviation Monitoring Bárðarbunga Volcanic Activity Summer 2014
http://www.wsi.com/blog/aviation/wsi-aviation-monitoring-bardarbunga-volcanic-activity-august-2014-2/
http://www.wsi.com/blog/wp-content/uploads/simulation-21Aug_C.jpg

The two 4.0 and 4.2s from several hours ago have been upgraded to a 4.0 and 4.6 and added to by a 3.8. The relatively ‘tame’ Gjlap eruption in 1996 was triggered by several large 4s followed by a 5.6.
The density of ice is ~1.0 and density of solid basaltic rock is ~2.9, so a 700 m thick ice sheet may sound like a lot of weight and blockage but it’s only a minor equivalent to about 220 m of rock overburden. Plus it has the mechanical fragility of soft glass with a lot more flexibility.
The main obstacle is therefore melt water quenching, not ice. An initial magmatic-phreatic explosion can clear a path in the overburden ice and water in about 2 seconds if it erupts with a serious head of lava fountaining into ice. In which case a Maar crater will form, which is wide steam explosion which are great at clearing all sorts of annoying trifling overburden like a major icesheet.
So it can stay under ice for days, weeks like a simmering Mr, Grumpy, or it can appear in two seconds and roar from a giant crater. All possibilities are open to it as Grimsvotn, did not mess around long in 2011, it exploded through the ice and was in the stratosphere in a few seconds – these two are twins. But Grimsvotn didn’t have as large and rapid a major magma intrusion volume.
And any one who has read the Laki 1783-4 accounts would not be breathing a sigh of relief if it turns out to be a major fissure eruption, least of all the airlines because even without ice and lots of water for added convection, Laki still filled the air of the entire northern hemisphere with super fine solid detritus.
The only upside in this case is there should be so much water released that it would tend to wash a lot of ash out with rain downwind. But don’t forget the accounts of hail mass kills of livestock out of the blue during the much drier 1783 Laki eruption. Also, apparently the ash subsidence generated a major chill in England via sinking ash deflecting the upper atmosphere closer to the ground in the summer and briefly frosted and froze the UK before the sulfur laden dust heat-inversion took over for weeks or months.
The point is a lot of a-typical things can occur which we never thought were natural variables. We can get a re-education here … or not.

The key takeaway from that 5.3 in the caldera western side was it occurred at 10 km depth, i.e. not from roof structure slump.
http://volcanodiscovery.com/bardabunga-earthquakes.html

A new harmonic tremor surge is just beginning in the last few minutes. This is the first increase since the large seismic swarm yesterday.

OK, they have reclassified the previous mag 5.3 from 10km depth to 5 km depth, on the western side of the caldera
And the new mag 5.1 is at 6 km depth and on the eastern side of the caldera.

Coupled with the effects of grand solar minimum of solar cycle 24, this Icelandic eruption will send the big FU to man-made climate changer freaks.

Just to mention that in the prelude to the Gjlap eruption in 1996, a paper I read about that said the Bardabunga area had several low mag 5 level quakes over the preceding decade. I think I posted a link to the paper in the first Bardarbunga thread.

Lots of 2+ quakes (15 last 30 min) up and down most of the length of the primary focus of activity over last 30 minutes from over 5km deep to 1.1km deep. Looks like there might be motion up nearly the full length of the column now in fits and starts.

should be, “… has [now] exceeded …”

Yep a couple hours ago all the activity was down near 10-12 km depth looks like a slug of material is working its way up to the surface. Now tremors are in the 1.8-4.9 km depth range