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In just one day, volcanic ash spewing forth from Iceland’s Eyjafjallajokull has brought airports to a halt all across Europe. The last time this volcano blew, it was deadly, emitting large quantities of toxic fluoride gas. Word Eyjafjallajökull literally means “Island Mountain Glacier”.

Iceland sits on a large volcanic hot spot in the Atlantic’s mid-oceanic ridge. Eruptions, common throughout Iceland’s history, are often triggered by seismic activity when Earth’s plates move and when magma from deep underground pushes its way to the surface. Iceland’s Laki volcano that erupted in 1783, freeing gases that turned into smog was mentioned in one article before and now point is on Eyjafjallajokull volcano.

The last time Eyjafjallajokull erupted was in 1821, pouring tonnes of ash containing toxic fluoride gas into the atmosphere. It lasted not 24 hours, but 2 years until 1823, causing the deaths of many cattle and sheep through fluor poisoning. Eyjafjallajokull has had four eruptions in the last thousand years: in 920, 1612, 1821-1823 and now in 2010. All of the previous eruptions were precursors to more massive activity from the neighboring Katla volcano but as yet geologists have not registered any seismic activity. Katla, located under the massive Myrdalsjokull icecap, threatens disastrous flooding and explosive blasts when it blows.

Eyjafjallajokull, a glacier covering a volcano of 1,600 meters in height and with a crater of 3 to 4 km in diameter, started becoming unstable at the end of 2009, when a number of small earthquakes fueled by building pressure seven kilometers beneath the volcano gave rise to a peak in activity – 3,000 earthquakes were registered between March 3 and 5 this year. This in turn was followed by an eruption on March 20.

There were two further eruptions on April 13 and 14, under the glacier causing meltwater floods to force the evacuation of 800 people from the slopes. From Wednesday to Thursday a huge cloud of ash, which continues to billow from the volcano, spread eastwards, causing flights to be cancelled across Western and Northern Europe.

Apart from reducing visibility and affecting flight control mechanisms, volcanic ash can damage the engines of aircraft and according to international regulations, the risk is sufficiently high to merit a closing of air space. An aircraft engine takes in air, compresses it and turns it into thrust by expelling it at high speed. If the air is mixed with particles of ash, it can clog hydraulic and electronic systems.

The last time this volcano erupted in 1821-1823, sheep and cows on its slopes were killed by toxic fluoride gas which also affects horses and humans. Easily absorbed through the skin or eyes, a quantity as small as 28 mg per kilo of body mass is fatal. It is currently not possible to predict how long the ash cloud will remain over Europe’s skies, especially because if the volcano continues to spew forth tonnes of material every hour, the situation can only worsen if the wind continues to push the plume eastwards.

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