What was the cause of the Eyjafjallajokull volcanic eruption?

Answer 1

Seismic activity started at the end of 2009 and gradually increased in intensity until on 20 March 2010, a small eruption started that was 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 Europe's 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 of the eruption started on 14 April 2010 and resulted in an estimated 250 million cubic metres (330,000,000 cu yd) of ejected tephra. The ash plume rose to a height of approximately 9 kilometres (30,000 ft), which rates the explosive power of the eruption as a 4 on the Volcanic Explosivity Index.

By 21 May 2010, the second eruption phase had subsided to the point that no further lava or ash was being produced.

By the morning of 24 May 2010, the view from the web camera installed on Þórólfsfell showed only a plume of water vapour surrounded by a blueish haze caused by the emission of sulphurous gases. Seismic data showed that there were still low intensity earth tremors happening, but scientists at the Icelandic Meteorological Office (IMO) and the Institute of Earth Sciences, University of Iceland (IES) concluded that the volcano had returned to a dormant state.

Due to the large quantities of dry volcanic ash lying on the ground, surface winds frequently lifted up an "ash mist" that significantly reduced visibility and made web camera observation of the volcano impossible.