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The 2010 eruptions of Eyjafjallajökull were volcanic events at Eyjafjallajökull in Iceland which, although relatively small for volcanic eruptions, caused enormous disruption to air travel across western and northern Europe over an initial period of six days in April 2010. Additional localised disruption continued into May 2010. The eruption was declared officially over in October 2010, when snow on the glacier did not melt. From 14–20 April, ash covered large areas of northern Europe when the volcano erupted. About 20 countries closed their airspace to commercial jet traffic and it affected about 10 million travellers. Seismic activity started at the end of 2009 and gradually increased in intensity until on 20 March 2010, a small eruption started rated as a 1 on the volcanic explosivity index. Beginning on 14 April 2010, the eruption entered a second phase and created an ash cloud that led to the closure of most of the European IFR airspace from 15 until 20 April 2010. Consequently, a very high proportion of flights within, to, and from Europe were cancelled, creating the highest level of air travel disruption since the Second World War. The second phase resulted in an estimated (0.25 km3) of ejected tephra and an ash plume that rose to a height of approximately , which rates the explosive power of the eruption as a 4 on the volcanic explosivity index.〔Erica R. Hendry "(What We Know From the Icelandic Volcano )", ''Smithsonian (magazine)'', 22 April 2010. Retrieved April 2010.〕 By 21 May 2010, the second eruption phase had subsided to the point that no further lava or ash was being produced. By the evening of 6 June 2010, a small new crater had opened up on the west side of the main crater. Explosive activity from this new crater was observed with emission of small quantities of ash. Seismic data showed that the frequency and intensity of earth tremors still exceeded the levels observed before the eruption, therefore scientists at the Icelandic Meteorological Office (IMO) and the Institute of Earth Sciences, University of Iceland (IES) continued to monitor the volcano. In October 2010, Ármann Höskuldsson, a scientist at the University of Iceland Institute of Earth Sciences, stated that the eruption was officially over, although the area was still geothermally active and might erupt again. ==Background== (詳細はice caps located in the far south of the island. It's situated to the north of Skógar and to the west of the larger ice cap Mýrdalsjökull. The ice cap covers the caldera of a volcano high, which has erupted relatively frequently since the last ice age. The most recent major eruptions occurred in 920, 1612 and from 1821 to 1823. Previous eruptions of Eyjafjallajökull have been followed by eruptions at its larger neighbour, Katla. On 20 April 2010 Icelandic President Ólafur Grímsson said that, "the time for Katla to erupt is coming close ... we () have prepared ... it is high time for European governments and airline authorities all over the world to start planning for the eventual Katla eruption". The volcanic events starting in March 2010 were considered to be a single eruption divided into phases. The first eruption phase ejected olivine basaltic andesite lava several hundred metres into the air in what is known as an effusive eruption. Ash ejection from this phase of the eruption was small, rising to no more than into the atmosphere. On 14 April 2010, however, the eruption entered an explosive phase and ejected fine glass-rich ash to over into the atmosphere. The second phase was estimated to be a VEI 4 eruption, which was large, but not nearly the most powerful eruption possible by volcanic standards. By way of comparison, the Mount St. Helens eruption of 1980 was rated as 5 on the VEI, and the 1991 eruption of Mount Pinatubo was rated as a 6. This second phase erupted trachyandesite. What made this volcanic activity so disruptive to air travel was the combination of these factors: # The volcano was directly under the jet stream. # The direction of the jet stream was unusually stable at the time of the eruption's second phase, continuously south-east. # The second eruptive phase happened under of glacial ice. The resulting meltwater flowed back into the erupting volcano, which created two specific phenomena: ## The rapidly vaporising water significantly increased the eruption's explosive power. ## The erupting lava cooled very fast, which created a cloud of highly abrasive glass-rich ash. This caused a large number of flights to be cancelled in the U.K. # The volcano's explosive power was enough to inject ash directly into the jet stream. Without this combination of factors, the eruption of Eyjafjallajökull would have been a medium-sized, somewhat nondescript eruption of little interest to those outside the scientific community or those living nearby. However, the above factors were precisely those needed for the jet stream to carry the ash directly over northern Europe into some of the busiest airspace in the world. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「2010 eruptions of Eyjafjallajökull」の詳細全文を読む スポンサード リンク
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