Can planes avoid the ash if they fly at lower altitudes?
Prof Jon Davidson says: “This is not a sensible option as it would take up too much fuel.”
Dr Claire Horwell adds: “The ash is falling to the ground so there’s still a problem. Likewise, the planes can't fly higher and, even if they could, they'd still have to descend through the cloud.” Have we got any better idea of when the eruption is coming to an end, or what are the signs to look out for?
Dr Colin Macpherson says that signs of decreased volcanic activity include:
· A decrease in the effusion of ash from the volcano, which experts will be able to observe visually.
· A decrease in the volume of flood water being generated by ice melt – something the Icelandic authorities are monitoring.
· A decrease in the amount of seismic tremor measured around the volcano. As there is less magma moving about under the volcano it will cause less upheaval and shaking. Again there will be close monitoring because this is a region of high risk.
· A decrease in steepness of volcano slopes. The volcano inflates like a balloon when there is magma within it, then deflates as the eruption subsides. Tilt meters, GPS and satellite dataare used to measure how the shape of the volcano changes.
· There may also be changes in the chemistry of groundwater around the volcano. Chemicals added by the volcano decrease in abundance as the amount of magma there decreases and/or solidifies. However, sampling ground water may be a challenge at present. As the ice over the eruption site melts, will that mean that the ash becomes less damaging?
Prof Jon Davidson says: “It is possible that, as the ice melts, the vent becomes free of water and ice and the fragmentation efficiency decreases. Then the ash size will be a little coarser (for a given eruption type) and may not get as far up into the atmosphere.” Is the carbon dioxide the volcano is spewing out more or less than the cancelled flights would have produced?
Prof Jon Davidson says: “This is a complex question - what about all the "extra" trains, buses etc that will be used to satisfy demand? And in terms of climate, what about all the sulphur dioxide which would form aerosols and have a cooling effect?
Dr Colin Macpherson, who has been calculating the carbon dioxide output from the volcano, says that using preliminary observati##被过滤## that the output is 150,000 tonnes per day but there is a large uncertainty on this estimate. Why has this caused so much grief to Europe when other erupti##被过滤## in the world don't seem to cause a meltdown?
Prof Jon Davidson says: “This eruption is very ordinary and unremarkable. It’s the fact that it happens to be combined with local weather systems which push the ash over North European airspace.
“There have been several incidents of aircraft flying into ash plumes, for example in the Aleutian Islands in Indonesia, with thankfully no casualties.
“In other parts of the world, volcanic ash has interrupted air traffic, for example with the eruption of Mount Ruapehu, New Zealand. In most cases, erupti##被过滤## have not been sustained for long periods and winds have not dispersed them into critical airspaces.
“The period of widespread commercial flying is less than 50 years, so we haven't yet encountered anything like the diversity of volcanic eruption possibilities that might be produced.
“It’s only in the last 30 or so years that we have recognised volcanic ash as a potentially serious threat to aviation. The first international symposium on volcanic ash and aviation safety was in 1991.” How much more/less of the sun's energy is being blocked out by the ash than is normally blocked out by aircraft contrails?
Prof Jon Davidson says: “The ash will not be a long term problem. It will more likely be the more likely the sulphur dioxide which forms aerosols and could block some incident sunlight. Even so, this is still a minor eruption and effects will be negligible. Is there anything we could do to limit the spread of ash?
Professor Jon Davidson says: “There is nothing we can do. What we could hope for is a way to better track the ash and to determine its density and know how the ash density maps onto hazard for aircraft, which I don't think we do.” Is it safe for my children to play outside?
Dr Claire Horwell says: “Yes. You may find it helpful to visit the website of The International Volcanic Health Hazard Network for more information Will the ash from Iceland be a recurring problem this year?
Professor Jon Davidson says: “This depends on two "weathers"- whether the eruption continues and how its intensity and capacity to fragment and carry ash upwards varies, and the weather as in the directi##被过滤## that sash is dispersed.” What are the risks of the eruption triggering the larger Katla volcano?
Dr Colin Macpherson says: “It appears that the last three erupti##被过滤## of Eyjafjallajoekull were followed by erupti##被过滤## at Katla. This is a recorded fact.
“At present there is no direct evidence for activity spreading to Katla, but it is something that the Icelandic seismologists will be monitoring carefully.” How are volcanoes monitored? How can you tell one is about to erupt and when?
Dr Dougal Jerram says: “We can use a variety of techniques. Seismic monitors can be used for earthquakes which can be created by movement of magma underground.
“We use tilt meters on the sides of volcanoes to see if the ground is moving. We can look at the different gases coming out of a vent to look for changes. We can monitor using satellite data to look for ground deformation and where ash plumes are going.
“You often get swarms of earthquakes and land swell, days and hours leading up to erupti##被过滤##.”作者: 魔鬼的尘埃 时间: 2010-4-23 08:43
恩 很学术的说法！