Iceland volcanoes may erupt more with global warmingWe just posted on the pulses of volcanism that r

Iceland volcanoes may erupt more with global warmingWe just posted on the pulses of volcanism that result from the cycle between glacial and interglacial eras caused by the redistribution of the weight of water between land and ocean as sea levels and ice sheets wax and wane in inverse proportion (see fb.me/472nd8pFN). These changes are linked to wobbles in the planet’s orbit around the sun and their effects on climate and sedimentation patterns (for a clear explanation of these wobbles, see our past post on astronomical rocks at http://on.fb.me/1zrSqRi). Evidence recently obtained using GPS receivers placed around Iceland has provided us with a wonderful example of the phenomenon. GPS stations are used by geologists for many things other than the obvious finding their way and marking the coordinates of any interesting rocks that they might come across. Global arrays tell us how far and in which direction tectonic plates move each year, and the rise and fall of the land, whether due to tectonic uplift/depression or isostatic rebound of land masses, as the pliable layer of the upper mantle on which the continents float (see http://on.fb.me/1C6rh6d) slowly expands after the melting of an ice sheet. The network is also used in earthquake and volcanic research.It was known for centuries (before the ice ages were even recognised as having existed) that areas once covered in ice sheets were rising. Scandinavia, Canada, Scotland and others all exhibited multiple raised terraces of old beaches around their coastlines, and the carving of marks in the 1600’s was used in the 1800’s to get a first estimate of the rate of rise. Later shells on these beaches were dated, constraining it further, and now GPS provides millimetre accuracy measurements. Iceland turns out to be rising even faster than previously thought, up to 3.5cm a year in the areas under the shrinking ice caps, and that the rate seems to have increased greatly over the last three warmer decades.The research settled the debate over how much of the uplift was due to ice loss after the ice age and how much came from the modern round of global warming. It showed a clear acceleration in uplift since 1995, and related it to increasing melting rates (which have also been quantified with fieldwork that shows the melting pace picking up since 1995). The acceleration was greatest under the ice caps and least in the regions far away from the glaciers.The rise leads to the decompression melting we discussed in our post linked in the first sentence. The release of the pressure of the ice’s weight on the rocks also allows volcanoes that are primed and ready to pop to go off when their critical point is reached and the lid blows out. The reduction in weight allows gases to come out of solution, increasing the pressure on the solidified magma plugging the volcano’s plumbing system.With three eruptions in five years (one of which shut down Atlantic airspace for a week), researchers are wondering to what extent the rebound is responsible, and what more might arise as the ice caps continue to melt. Field evidence suggests a large pulse in volcanism (a roughly 30 fold increase on background rates) during the great melt 12,000 years back, and the team think that this effect may already be returning into play.The important question is what this means for other glaciated regions that are also fast melting. How many primed, locked and loaded volcanoes lurk under the world’s ice sheets? Magma is known to be stirring under Antarctica, Greenland may have unknown volcanoes, and more importantly the north and south Patagonian ice caps sit atop regions containing known supervolcanoes and a host of lesser fry. Even single peaks such as Rainier and Kilimanjaro may erupt as their glaciers melt, it depends how close to the critical pressure the magma system is. There may be some nasty surprises lurking around the corner.Bill McGuire, a renowned volcanologist, wrote an excellent book on this complex topic called ‘Waking the Giant: Volcanism and Climate’ a couple of years ago that I heartily recommend to those who wish to take it further.LozImage credit, Grimsvotn erupting in the Vatnajokull ice cap: Oddur Sigurdsson -- source link

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