Friday, May 7, 2010

Ash-termath

For any of those who were travelling over the last few weeks you will know all too well how a volcano called Eyjafjallajokull can make for an unpleasant trip. Flights throughout Europe have seen cancellations since the eruption started back in March. Volcanoes can have a major impact on the climate, so how if any will this eruption have an effect on our climate?

When volcanoes erupt they eject ash and various gases into the atmosphere. The ash is comprised of pumice and crushed rock. The height that this ash gets thrown to can lead to aircraft being grounded. Current jet aircraft operate at an altitude of 9-15 km. The ash ejected can damage the turbine blades on a jet engine. The temperatures within a jet engine are hot enough to melt this ash and it can re-solidify on the internals in the engine which can lead to tragic consequences.

Volcanoes emit vast quantities of gases, these gas emissions are dependant on the type of eruption. Of these gases water vapor, carbon dioxide and sulphur dioxide are the most common. All these gases we commonly refer to as greenhouse gases. Of these gases sulphur dioxide poses the greatest risk. Not only does it readily convert into sulfuric acid which can fall back to earth as acid rain, it can also condense into sulfate aerosols in the upper atmosphere. These aerosols when present in the upper atmosphere act like a mirror reflecting the sun's rays back into space. This can reduce average global surface temperatures across the planet by up to 0.5K. This phenomena is referred to as a volcanic winter. The most recent of these winters occurred in 1991 when Mount Pinatubo erupted in massive explosion of gases and ash.


In this eruption 10 cubic kilometres of material was ejected into the atmosphere along with nearly 20 million tons of sulphur dioxide. When this sulphur dioxide condense in the stratosphere it triggered a global temperature drop of 0.5K.


Looking at the temperature trend during the 90's there is a very obvious bump due to the eruption of Pinatubo. There have being several other of these climate changing events in recorded human history. Several famines during the 18th and 19th centuries have been associated with volcanic eruptions. So what effect then will this newest eruption have on our delicate climatic system?

Initial reports from the Instituto Nazionale di Geofisica e Vulcanologia estimate that the Eyjafjallajokull volcano has ejected about 120-150 million cubic meters of material. This material reached a height of about 7km in the atmosphere hence the problem with flights. This amount of material is relatively small in comparison to some of the major events. It is the current thinking that this will only have a minor local effect on the atmosphere in and around Iceland. However it must be added that we have no idea how long this current eruption will last. When  Eyjafjallajokull last erupted in 1821 it continued to erupt for over 14 months. So we could see disruption to flights on going for months to come.

I will leave you with a sobering thought, as bad as this volcano is perceived to be be there is a far more dangerous threat lying in wait. Almost 70,000 years ago a volcano called Mount Toba erupted in vast explosion. This 'super-eruption' trigger a winter that last between 6-10 years globally and almost wiped out the human species. Current thinking among seismologists point to a similar event happening in the future in Yellowstone National Park, Wyoming, USA.

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