Well, this is a very interesting graph. I’d not heard of a ‘cumulative seismic moment’ before, but it looks like a formal mathematical way of doing what I’m doing “intuitively” when I watch for a ramp up in number and size of quakes. This, as they say, will bear more investigation / learning…
But back at this volcano… When it goes, things are going to be messy in Iceland and probably “a bad day” in Europe as well.
What SSam had to say:
Grímsvötn along with Bárðarbunga, are the two dominant central vent volcanoes that sit under the Vatnajökull icecap with the five other volcanoes quietly biding their time.
The wiki is none too soothing either:
The Grímsvötn lakes (Icelandic: vötn, singular: vatn) are lakes in Iceland. They lie in the highlands of Iceland at the northwestern side of the Vatnajökull glacier and are covered by its ice cap. Beneath them is the magma chamber of a volcano. The location of the lakes is 64°25′N 17°20′W, at an elevation of 1,725 m (5,659 ft).
Grímsvötn has a southwest-northeast-trending fissure system, and the massive climate-impacting Laki fissure eruption of 1783-1784 was a part of the same fissure system. Grímsvötn was erupting at the same time as Laki during 1783, but continued to erupt until 1785. Because most of the volcano lies underneath Vatnajökull, most of its eruptions have been subglacial.
Harmonic tremor was recorded twice around Grímsvötn on 2 and 3 October 2010, potentially indicating an impending eruption. At the same time, sudden inflation was measured by GPS in the volcano, indicating magma movement under the mountain. On 1 November 2010 meltwater from the Vatnajökull glacier was flowing into the lake, suggesting that an eruption of the underlying volcano might be imminent.
Subglacial eruptions regularly give rise to glacial bursts as jökulhlaups. Eruptions may melt enough ice to fill the Grímsvötn caldera with water, and the pressure may be enough to suddenly lift the icecap, allowing huge quantities of water to escape rapidly. As a result, the Grímsvötn caldera is monitored very carefully by scientists. When a large eruption occurred in 1996, geologists knew well in advance that a glacial burst was imminent. It did not occur until several weeks after the eruption finished, but the monitoring let the Icelandic ring road (Hringvegur) be closed when the burst occurred. A section of road across the Skeiðará sandur was washed away in the ensuing flood, but no-one was hurt.
A week-long eruption occurred at Grímsvötn starting on 28 December 1998, but no glacial burst occurred. In November 2004, another eruption of about one week began. Volcanic ash from the eruption fell as far away as mainland Europe and caused short-term disruption of airline traffic into Iceland, but again no glacial burst followed the eruption.
So this guy definitely needs some watching. One can only hope any new eruption will be a small one like 2004.
Now I’m wondering just how commonly used and reliable this metric is for predicting volcanic activity… and it gives me even more reason to worry about the increased non-fault located earthquakes showing up on the quake watch pages. The prediction of the ‘common cause for cooling and quakes’ thesis is that they all come together when they come. This ought to manifest first as some cooling and some increased quake activity. And we’ve got some cooling and some increased quake activity. Then we ought to start seeing minor volcano news (check, got that..) and then some very significant cooling (maybe have that, need about a year to know) and then a Big One volcano lets loose. But that ought to be preceded by some proximal earthquake storms.
This is going to be “interesting times”…
That’s a lot of quakes on the map as I’m typing this. 158 in the Northern Hemisphere.