Between March and June 2010 a series of volcanic events at Eyjafjallajökull in Iceland caused enormous disruption to air travel across Western Europe.

[2] Seismic activity started at the end of 2009 and gradually increased in intensity until on 20 March 2010, a small eruption began, rated as a 1 on the volcanic explosivity index.

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.

On 14 April 2010, however, the eruption entered an explosive phase and ejected fine glass-rich ash to over 8 km (26,000 ft) into the atmosphere.

Teams from the Icelandic Association for Search and Rescue were stationed at the eruption site as part of standard safety measures and to assist in enforcing access restrictions.

Vodafone and the Icelandic telecommunications company Míla installed webcams, giving views of the eruption from Valahnúkur, Hvolsvöllur, and Þórólfsfell.

A study by the Icelandic Meteorological Office published in December 2009 indicated an increase in seismic activity around the Eyjafjallajökull area during the years 2006–2009.

[17] The radar stations of the Meteorological Institute of Iceland did not detect any appreciable amount of volcanic ashfall during the first 24 hours of the eruption.

[18] However, during the night of 22 March, they reported some volcanic ash fall reaching the Fljótshlíð area (20 to 25 km or 12 to 16 mi northwest of the eruption's location)[19] and Hvolsvöllur town (40 kilometres (25 mi) northwest of the eruption location)[19] leaving vehicles with a fine, grey layer of volcanic ash.

[21] By 26 March 2010, the global positioning system (GPS) equipment used by the Iceland Meteorological Office at Þorvaldseyri farm in the Eyjafjöll area (around 15 km or 9.3 mi southeast of the location of the recent eruption)[19] had shown 3 cm of displacement of the local crust in a southward direction, of which a 1-cm displacement had taken place within four days.

About 500 farmers and their families had to escape from the areas of Fljótshlíð, Eyjafjöll, and Landeyjar were evacuated overnight (including a group of 30 schoolchildren and their three teachers[26][27] from Caistor Grammar School in England), and flights to and from Reykjavík and Keflavík International Airport were postponed, but on the evening of 21 March, domestic and international air traffic was allowed again.

[28][29][30] Inhabitants of the risk zone of Fljótshlíð, Eyjafjöll, and Landeyjar area were allowed to return to their farms and homes after an evening meeting with the Civil Protection Department on 22 March and the evacuation plan was temporarily dismissed.

[34] This rise in water temperature was thought to be related to the eruption nearby and was affecting part of the Krossá drainage basin.

[42] Crustal expansion continued at Þorvaldseyri for two days after the eruption began, but was slowly decreasing whilst the volcanic activity was increasing.

No unusual seismic activity was detected at the time the new fissure appeared, nor any crustal expansion according to many seismometers and GPS recorders situated in nearby areas.

Visual observations were greatly restricted due to cloud cover over the volcano, but an aeroplane of the Icelandic Coast Guard imaged eruptive craters with radar instruments.

[citation needed] Samples of volcanic ash collected near the eruption showed a silica concentration of 58%—much higher than in the lava flows.

Agriculture is important in this region of Iceland,[48] and farmers near the volcano have been warned not to let their livestock drink from contaminated streams and water sources,[49] as high concentrations of fluoride can have deadly renal and hepatic effects, particularly in sheep.

[50] The Icelandic Food and Veterinary Authority released an announcement on 18 April 2010, asking that all horse owners who keep their herds outside be on the alert for ash fall.

Cold water from melted ice quickly chilled the lava, causing it to fragment into highly abrasive glass particles that were then carried into the eruption plume.

Pulsating explosive activity on 17 April 2010, able to be observed because of the fine weather, was later understood to be due to periodic clogging/plugging of the conduit associated with the rise and degassing of more magma.

By the morning of 24 May 2010, the view from the web camera installed on Þórólfsfell[55] showed only a plume of water vapour surrounded by a bluish haze caused by emission of sulphurous gases.

[56] On 21 June 2010, data from seismic recorders in the area indicated that the frequency and strength of earth tremors had diminished, but were continuing.

[59] The IES updated the eruption flow rate on 21 April 2010 to an estimation less than 30 cubic metres per second (1,100 cu ft/s) of magma, or 75 t/s, with a large uncertainty.

While some ash fell on uninhabited areas in Iceland, most had been carried by westerly winds, resulting in the shutdown of airspace over much of Europe.

The Icelandic flag carrier airline, Icelandair, seemed at first especially vulnerable, but managed to deal effectively with the eruption, and subsequently published a detailed report about its actions and conclusions.

Large-scale release of sulphur dioxide into the troposphere also poses a potential health risk, especially to people with pre-existing breathing disorders.