{"id":170,"date":"2011-05-22T15:39:08","date_gmt":"2011-05-22T14:39:08","guid":{"rendered":"http:\/\/all-geo.org\/volcan01010\/?p=170"},"modified":"2011-05-22T15:43:26","modified_gmt":"2011-05-22T14:43:26","slug":"grimsvotn-eruption-frequently-asked-questions","status":"publish","type":"post","link":"https:\/\/all-geo.org\/volcan01010\/2011\/05\/grimsvotn-eruption-frequently-asked-questions\/","title":{"rendered":"Grimsv\u00f6tn eruption – frequently asked questions"},"content":{"rendered":"

Iceland’s most active volcano, Grimsv\u00f6tn, began erupting last night.\u00a0 Fire and Ice yet again, baby!\u00a0 Here are some answers to questions that you might have.<\/p>\n

Why are you so excited?<\/h3>\n

Because it’s big!\u00a0 This is the most powerful eruption in Iceland in over 50 years.\u00a0 Radar measurements, pilot reports and ground observations estimate that the ash-rich eruption plume reached 17 km last night.\u00a0 By comparison, the Eyjafjallaj\u00f6kull plume of last year was 6-9 km high.\u00a0 This is important because every extra kilometre of plume requires a much faster eruption rate.\u00a0 The diagram below, taken from a paper by Mastin et al (2009)<\/a> compares data from past eruptions.<\/p>\n

\"\"<\/a><\/p>\n

The diagram shows that an eruption such as Eyjafjallaj\u00f6kull, with a plume of ~7 km corresponds to an eruption rate of 105<\/sup> m3<\/sup>s-1<\/sup> (10 x 10 x 10 x 10 x 10, or 10,000 cubic metres per second).\u00a0 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<\/sup> to 108<\/sup> m3<\/sup>s-1<\/sup>, 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 Eyjafjallaj\u00f6kull plume which was not as sustained.<\/p>\n

If it’s so big, why is there so little fuss?<\/h3>\n

The Eyjafjallaj\u00f6kull 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 ash.<\/p>\n

    \n
  1. Fine ash grains fall to the ground much more slowly than big ones, so the distal impacts of an eruption depend on how much fine ash it produces.\u00a0 The proportion of fine ash depends on the composition of the magma, and if it interacts with water (e.g. from a glacier).\u00a0\u00a0 The Eyjafjallaj\u00f6kull eruption involved sticky, bubbly magma, more than 90% of which formed grains less than 1 mm across.\u00a0 It was explosive when it melted through the glacier, but also once the interaction with meltwater had ended.\u00a0 By contrast, Grimsv\u00f6tn usually erupts basalt magma, which is rarely explosive by itself and is only explosive now because of the meltwater.\u00a0 The fragmentation is less efficient and the proportion of fine ash is lower.<\/li>\n
  2. During the Eyjafjallaj\u00f6kull eruption, there was a high pressure system over the north Atlantic whose northwesterly winds brought the ash right down into Europe.\u00a0 For the moment, the winds are sending the bulk of the ash northwards into the Arctic.\u00a0\u00a0 The plot produced by the UK Met Office shows the predicted ash dispersion until Monday morning.\n

    \"\"<\/a>

    Predicted ash distribution map from the Met Office. 22 May 2011.<\/p><\/div><\/li>\n

  3. Prior to the Eyjafjallaj\u00f6kull eruption, the rules were that aviation had to AVOID ALL ASH.\u00a0 Now they are different, and where planes can fly is based on zones of different ash concentration.\u00a0 There are real issues<\/a> with whether we are actually\u00a0 able to measure\/estimate the boundaries of these zones with real confidence, but the upshot is that even if we had an exact repeat of the Eyjafjallaj\u00f6kull 2010 eruption, the disruption to air travel would be a fraction of what we saw last year.<\/li>\n<\/ol>\n

    So my flight on Wednesday morning will be fine, then?<\/h3>\n

    <<WARNING: SPECULATION AHEAD>><\/p>\n

    Not necessarily.\u00a0 Most recent Grimsv\u00f6tn eruptions have lasted a few days to a week.\u00a0 The most recent one, in 2004, lasted 4 days and erupted the bulk of its ash in the first 36 hours.\u00a0 The Met Office surface pressure chart shows the wind moving to the northwest from Tuesday.<\/p>\n

    An individual grain of fine ash (<63 microns in diameter), falling from 17 km, can travel 1000 km before it lands, which would take it safely into Scotland.\u00a0 Although Grimsv\u00f6tn is producing relatively little fine ash proportionally<\/em>, the much larger eruption rate means that it is still producing a significant amount overall<\/em>.\u00a0 If the eruption continues, then I wouldn’t be surprised if there were UK airport closures.<\/p>\n

    We’ll see what happens…<\/p>\n

    What about local effects?<\/h3>\n

    Iceland is a country about the size of Ireland.\u00a0 For 9 months of the year, you cannot cross the middle as the roads are blocked by snow.\u00a0 Highway 1 is the tarmac ring-road that runs around the country near the coast.\u00a0 The authorities have closed this where it crosses the Skeidarasandur outwash plain in anticipation of a j\u00f6kulhlaup<\/a> (glacial flood) when the meltwater escapes the glacier.\u00a0 This means that you can no longer drive directly from V\u00edk in the south, to H\u00f6fn in the south east (271 km, about 3 hours).\u00a0 Instead, you have to go all the way round the other way (1068 km, about 13 hours).\u00a0 If the j\u00f6kulhlaup damages the bridges, then the road could be closed for weeks.\u00a0 Nightmare!<\/p>\n

    Closer to the volcano, the ash is falling fast.\u00a0 Locals have been told to bring in their livestock and to wear dustmasks and goggles.<\/p>\n

    Where can I find out more?<\/h3>\n