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Volcanic eruption and water

^{Gígjökull, Eyjafjallajökull’s largest outlet glacier. Picture: Andreas Tille / GNU Free Documentation License}

Docent Arto Luttinen teaches volcanology at the Department of Geology of the University of Helsinki. He explains the specific features of subglacial volcanic activity:

Iceland is a volcanic island located above a major fracture system. New magma is constantly being generated and stored in deep magma chambers. Every now and then, the pressure of the magma overcomes the strength of the overlying bedrock and the magmas erupt as lava. There are presently some 20 active volcanoes in Iceland. Thanks to the composition of the magma, the eruptions typically are rather calm and only produce lava flows and minor quantities of volcanic gases.

However, some of the active Icelandic volcanoes have grown high enough so that their summits are covered with glaciers. For example, Vatnajökull, the largest glacier in Europe, is underlain by a great volcano called Grimsvötn. These glaciated volcanoes are sites where dramatic explosive eruptions have occured, most recently at the Eyjafjallajökull (Eyjafjöll) volcano in SE Iceland.

When molten rock and ice come together, the melt solidifies as volcanic glass and ice becomes water. These transformations are nearly instantaneous and very violent. The volume change associated with the formation of water vapour is explosive and shatters the newly formed volcanic glass into solid particles, tephra. A hot mixture of vapour generated from the ice and glass particles and volcanic gases generated from the magma comprise a rapidly ascending eruption column. Larger particles fall down nearby, whereas the finest solid material, called volcanic ash, is carried upward by the hot flow of gas. Great floods of water are released from the glacier and cause havoc around the volcano.”

From the depths into the atmosphere

Ilkka Pollari works as the Director of Kemira’s Espoo Research Centre. He is also the chairman of Water group for the upcoming Millennium Youth Camp. Pollari discusses the effects of volcanic activity on water:

“In the recent volcanic eruption, both lava and gaseous substances met primarily with ice and secondly – as ice melts – with water. The powerful flow of hot gas – mostly sulphur dioxide and water vapor – carries with it large quantities of mineral particles – mostly below 0.1 mm in diameter. These particles have at the early stages of this rather powerful eruption reached up to 10 km height.

The small particles offer a seed for condensation of water vapour, if relative humidity is high. This will increase the possibility of the small particles starting to fall lower towards the ground, occasionally accelerated and “washed down” by rainfall. Typically, however, the atmospheric humidity in stratosphere (higher layer of atmosphere) is low and for this reason the volcanic ash typically prevail in upper atmosphere for months.

Sulphur dioxide of the volcanic gases dissolves into liquid water and droplets in the atmosphere and quickly reacts to form sulphurous acid H₂SO₃ (note, one oxygen atom less than in the stronger, more familiar sulphuric acid H₂SO₄). Early in the eruption, an estimated 3000 tons (as sulphur) per day was emitted from the Eyja volcano in Iceland. This daily emission corresponds to some 5% of European annual industrial sulphur emissions.

Finnish Institute of Meteorology has not detected elevations in rainwater acidity pH, even though Finland has been quite much affected by recent volcanic ash clouds. Acid rain has been shown to have adverse impacts on forests, freshwaters and soils, killing insect and aquatic life-forms as well as causing damage to buildings and having impacts on human health.”

Elisa Lautala works as web editor for University of Helsinki's Faculty of Science. Elisa likes all kinds of cultural events, good books, warm weather, and aqua-jogging.