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Why Grímsvötn Is Proving Relatively Benign

Tiffany Tsai |
May 25, 2011 | 2:09 p.m. PDT

Staff Writer

Icelandic Volcano Eruption
Icelandic Volcano Eruption
If anyone had told the stranded travelers in Heathrow last April that Iceland would play host to a stronger, higher-plumed volcanic eruption the very next spring, their screams would probably have been audible all the way to the ash cloud.

A year later, Grímsvötn has blown its top, multiple European airports are calling stops to flights, and a 5-kilometer ash column hangs over the North Atlantic--yet no one is panicking.  Although air travel cancellations and delays currently plague fifteen countries outside of Iceland, experts channel an optimism unseen anywhere near Eyjafjallajökull's blast.

"Although we are partly dependent on the weather and the pattern of ash dispersion, we do not at this stage anticipate the widespread airspace closures and the prolonged disruption we saw last year," said European Union Transport Commissioner Siim Kallas in Spiegel.  

Europe's happy avoidance of continent-wide closures is owed greatly to revisions of crisis management guidelines spurred by last year's debacle.  But even within Iceland, roads not far from the volcano's ice cap site of Vatnajökull remain free for travel.  The official tourist website emphasizes that eruption effects are localized and speculates that the pendant ash plume may become a tourist attraction (scientists discourage volcano tourism, by the way).

Nature, not policy, has blown out the candles on its most recent fire child, it seems.  So if the worst is indeed over, what makes Grímsvötn such an obliging beast?

Magnús Tumi Guðmundsson, a professor of geophysics at the University of Iceland who focuses on subglacial volcanism, said "a lot of lightening [sic] accompanying it and a wide ash dispersal” when he flew over the volcano on Sunday.  Unlike the ominously still skies of 2010, the present Northern European troposphere contains enough wind to scatter the ash widely.  Ash, which has already reached England, is expected to blow northeast leading to possible dispersal over the Arctic.

Aside erupting into opportune weather, Grímsvötn represents the subglacial basaltic volcanic type, erupts more frequently than any other Icelandic volcano, and lies under the largest ice cap by volume in Europe, according to the University of Iceland.  Guðmundsson has told Ice News that Vatnajökull, Grímsvötn's ice cap, probably contains enough ice to seal the cap against new vents opening.  Without lava issuing forth, the eruption will spew only ash.

More importantly, the tephra, or erupted fragments, have been found to be coarser than in the Eyjafjallajökull plume.  Last July, the International Volcanic Task Force convened for the first time to discuss better ways of modeling volcano ash.  Their working paper explains that volcanos pack more or less ash into the air depending on plume shape, eruption rate, and plume height, but fragment size is key when determining the rate of fallout. Simple physical momentum dictates that fat apples fall first:

Fragments larger than several tens of microns can fall at a meter per second or faster, reaching the ground within several hours and usually within a few hundred kilometers of the volcano. Micron-sized fragments would theoretically fall at centimeters per second or less, staying in the atmosphere for days.

A team from the University of Cambridge, headed by Evgenia Ilyinskaya, published in March studies analyzing the size distributions of tephra from Eyjafjallajökull.  In the picture below, the vertical axis shows numbers and the horizontal axis diameters.  It can be seen that small particles dominate; moreover, fragments all come at micron scale, qualifying them for a mad whirligig"in the atmosphere for days."


The UK's National Air Traffic Services keeps a running list of updates on the ash movement.  As of Tuesday, it foresees a speedy resumption of flights: "Latest information from the Met Office shows that following the recent eruption of Grímsvötn in Iceland, no volcanic ash is currently predicted in airspace over the UK from 0100 UK time on Wednesday 25th May."  Looks like President Obama could have stayed in the land of the Moneygall Obamas, after all.


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Ilyinskaya, E., V.I. Tsanev, R.S. Martin, C. Oppenheimer, J.S. Le Blond, G.M. Sawyer and M.T. Gudmundsson (2011). Near-source observationsof aerosol size distributions in the eruptive plumes from Eyjafjallajokull volcano, March-April 2010. Atmospheric Environment.



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