![\"Met](\"http:\/\/all-geo.org\/volcan01010\/wp-content\/uploads\/2011\/05\/vaac_image.jpg\")
<\/a>Met Office predictions for ash dispersal on Tuesday and Wednesday (24th, 25th). The map shows ash being blown across the UK.<\/p><\/div>\n<\/dt>\n<\/dl>\n
But I heard that the ash grains from this eruption were too big to reach us.<\/h3>\n
It is true ash being produced by the Gr\u00edmsv\u00f6tn eruption is generally coarser that that from Eyjafjallaj\u00f6kull last year, but that is not the whole story.\u00a0 Volcanoes can eject magma at all sizes, from car-size blocks to tiny grains a millionth of a metre across.\u00a0 There is not just one unique grainsize, but a grainsize distribution.\u00a0 The fine ash (<64 microns) causes most problems, because it can travel further from the volcano before falling to the ground.\u00a0 All explosive eruptions produce some fine ash, but the relative proportion can vary.<\/p>\n
OK.\u00a0 So is the problem that the Gr\u00edmsv\u00f6tn eruption is really big?<\/h3>\n
Exactly.\u00a0 Even if the eruption was producing only 50% as much fine ash as Eyjafjallaj\u00f6kull, the material was being produced over 100 times more quickly, so we still end up with a lot of ash floating about.\u00a0 You can see what I mean with this simple two part experiment.\u00a0 (If anyone actually tries this out, can you post a video on youtube, please?\u00a0 I’d love to see it!)<\/p>\n
Part 1:<\/p>\n
- \n
- Mix together 2 parts icing sugar, 2 parts castor sugar, 2 parts coarse brown sugar and 2 parts sugar cubes in a coffee mug.<\/li>\n
- Go outside, and throw the mixture as high as you can up into the air.<\/li>\n
- The result is sugar cubes scattered around your feet and a puff of sweet-tasting dust drifting off in the wind.<\/li>\n
- Repeat steps 1+2 every half hour for a whole day. This is Eyjafjallaj\u00f6kull 2010.<\/li>\n<\/ol>\n
Part 2:<\/p>\n
- \n
- Mix together 1 part icing sugar, 1 part castor sugar, 3 parts coarse brown sugar and 3 parts sugarcubes, this time filling up a really big sauce pan.\u00a0 Proportionally<\/em>, this has half as much fine ash as before.<\/li>\n
- Go up to the second floor and throw it out the window.\u00a0 This is Gr\u00edmsv\u00f6tn 2011.<\/li>\n<\/ol>\n
We’re flying to Austria on Saturday.\u00a0 Do you think that we’ll get away?<\/h3>\n
As always, it depends on a combination of the weather and what the volcano is up to.\u00a0 I think that the chances are good, though.\u00a0 The low pressure system that was blowing the ash towards us will move past in the next day or so, and all indications are that the eruption is fizzling out.<\/p>\n
How can you tell that the eruption is ending?<\/h3>\n
The height of the eruption column has been declining, from 20 km on Sunday down to ~5 km at the moment.\u00a0 The height of the column is very sensitive to rate that material is erupted from the volcano, such that a halving in column height implies that the eruption rate has declined to a 16th of what it was before.<\/p>\n
![\"Declining](\"http:\/\/all-geo.org\/volcan01010\/wp-content\/uploads\/2011\/05\/plume_height.png\")
<\/a>Changes in height of the Gr\u00edmsv\u00f6tn plume. The decline corresponds to a massive reduction in the eruption rate. The plume heights are taken from the Met Office website.<\/p><\/div>\n
Are there any other signs?<\/h3>\n
Yes.\u00a0 Seismometers at the volcano have measured continuous small earthquakes during the eruption.\u00a0 This is called tremor, and is caused by movement of magma within the volcano.\u00a0 The intensity of the tremor has been declining since the eruption began.<\/p>\n
![\"Tremor](\"http:\/\/all-geo.org\/volcan01010\/wp-content\/uploads\/2011\/05\/grf.gif\")
<\/a>Tremor data from Gr\u00edmsv\u00f6tn, showing high, but declining tremor since the eruption began on the 21st May. The plot comes from the Icelandic Met Office website.<\/p><\/div>\n
Also, GPS measurements on the volcano detected the surface gradually rising since the last eruption, as the magma chamber beneath it inflated.\u00a0 Since the eruption began, the data show a subsidence of 25 cm, as the pressurised magma within the volcano is erupted and it deflates back down.\u00a0 With the pressure in the magma chamber released, the eruption will only pick up again if fresh magma arrives from deeper in the system.<\/p>\n
![\"GPS](\"http:\/\/all-geo.org\/volcan01010\/wp-content\/uploads\/2011\/05\/gps.png\")
<\/a>GPS data from Gr\u00edmsv\u00f6tn, recording the inflation of the volcano over the last 5 years. The final datapoints record a big deflation during the eruption. The plot comes from the Icelandic Met Office website.<\/p><\/div>\n
Therefore, unless another vent opens or new magma is injected, it is probable that the eruption will not pick up again and will end completely in the next few days.<\/p>\n
So will the ash just disperse?<\/h3>\n
Yes.\u00a0 The ash above us at the moment was erupted early in the eruption, and the current eruption rate is too low for newly-erupted ash to cause problems in Britain.\u00a0 As the cloud disperses some of the finest grains will remain airborne for days, but their concentration will be too low to cause problems.\u00a0 The new flight rules brought in during the Eyjafjallaj\u00f6kull eruption will get flights back in the air quickly, too.\u00a0 This plot from the BBC website last year shows how the area of airspace that would be out of action is made much smaller by the threshold-based system.<\/p>\n
![\"Flight](\"http:\/\/all-geo.org\/volcan01010\/wp-content\/uploads\/2011\/05\/iceland_ash_cloud_17_05_1800.gif\")
<\/a>A map published on the BBC website during the Eyjafjallaj\u00f6kull eruption. It shows how changing the rules so that planes only had to avoid ash above a certain concentration (red) instead of avoiding all ash (orange) opened up large areas of airspace.<\/p><\/div>\n
Will we see ash falling here?<\/h3>\n
I hope so.\u00a0 Last year some people saw ash falling, but the majority just saw blue skies.\u00a0 This even led some people to say that there was no ash<\/a> there at all.\u00a0 They were the first ever Ash Cloud Sceptics.\u00a0 They were wrong.\u00a0 Ash grains fell through the air, and in the rain.\u00a0 The figure below shows an example.\u00a0 The ash cloud was measured by lasers on the ground (LiDAR), and sampled during special research flights.\u00a0 The lasers and research planes will be in action again this week.<\/p>\n
![\"Ash](\"http:\/\/all-geo.org\/volcan01010\/wp-content\/uploads\/2011\/05\/rain_tephra.jpg\")
An ash grain from Eyjafjallaj\u00f6kull that was collected in rainwater near Leicester during the eruption last year. Note the glassy, translucent texture, angular shape, and bubbles in crystals within the grain. This grain was transported to the UK in the ash cloud.<\/p><\/div>\n
With the high winds and the rain, it may be very difficult to see the ash grains.\u00a0 They will be very small, like dust.\u00a0 If you do find some settling where you are, the British Geological Survey<\/a> would like a sample!\u00a0 Visit their ash collection website<\/a> to find out how you can help.<\/p>\n
The weather has been wild the past few days, and those scenes from Iceland are positively hellish.\u00a0 Does this have anything to do with the Rapture?<\/h3>\n
No.\u00a0 This has nothing to do with the Rapture.\u00a0 Was the end of the world also foretold by the Gr\u00edmsv\u00f6tn eruption in 2004?\u00a0 Or the one in 1998?\u00a0 How about 1996, 1984, 1983, 1972, 1954, 1948, 1945, 1941, 1939, 1938, 1934, 1933, 1922, 1919, 1910, 1902, 1897, 1891, 1887, 1883, 1873, 1867, 1861, 1854, 1838, 1823, 1816 or any of the hundreds before that?\u00a0 No.<\/p>\n","protected":false},"excerpt":{"rendered":"
As the eruption continues, here are some answers to some more common questions. Flights are being cancelled.\u00a0 Does that mean that ash is reaching the UK? Yes.\u00a0 It is falling in the Orkneys as I write this and the Met … Continue reading
- Go up to the second floor and throw it out the window.\u00a0 This is Gr\u00edmsv\u00f6tn 2011.<\/li>\n<\/ol>\n
- Mix together 1 part icing sugar, 1 part castor sugar, 3 parts coarse brown sugar and 3 parts sugarcubes, this time filling up a really big sauce pan.\u00a0 Proportionally<\/em>, this has half as much fine ash as before.<\/li>\n