Sunday, May 22, 2011

Grimsvötn eruption – frequently asked questions (and some speculations on flying)

From Volcan01010:
Iceland’s most active volcano, Grimsvötn, began erupting last night.  Fire and Ice yet again, baby!  Here are some answers to questions that you might have.

Why are you so excited?

Because it’s big!  This is the most powerful eruption in Iceland in over 50 years.  Radar measurements, pilot reports and ground observations estimate that the ash-rich eruption plume reached 17 km last night.  By comparison, the Eyjafjallajökull plume of last year was 6-9 km high.  This is important because every extra kilometre of plume requires a much faster eruption rate.  The diagram below, taken from a paper by Mastin et al (2009) compares data from past eruptions.

The diagram shows that an eruption such as Eyjafjallajökull, with a plume of ~7 km corresponds to an eruption rate of 105 m3s-1 (10 x 10 x 10 x 10 x 10, or 10,000 cubic metres per second).  This is equivalent to a few hundred tonnes per second in mass. An eruption with a 17 kilometre plume could have a discharge rate of 107 to 108 m3s-1, meaning that it is producing between 100 and 1000 times more material every second. These calculations are obviously only rough, and there are lots of complicating factors such as local weather conditions, the presence of ice over the vent and whether this comparison is even appropriate for the Eyjafjallajökull plume which was not as sustained.

If it’s so big, why is there so little fuss?

The Eyjafjallajökull eruption closed European airspace and cost billions of Euros. This eruption is much bigger, but so far only Keflavik airport (Iceland) is closed and the story is beneath the groundbreaking “Footballer Has Affair” on the BBC front page. The difference in impact on aviation comes down to three factors: the ash being produced by the eruption, the weather patterns blowing the ash around, and new rules about planes flying into....MORE