Harrow and Hillingdon Geological Society

Volcanic CAT Scan

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CAT scan of an active volcano: Three dimensional seismic tomography at Montserrat

Dr Michele Paulatto

In July 1995 the Soufriere hills Volcano on the island of Montserrat started erupting after a long period of quiescence. The eruption soon escalated and forced the evacuation of two thirds of the island’s population, including the capitol, Plymouth, which is now uninhabitable. The eruption is still on-going and is thought to be caused by the intrusion of hot magma into the shallow crust, which has heated up and remobilized older magma. The lava erupted at the surface is a mixture of the old and new magma and, because of its high crystal content, it is highly viscous. This property determines the eruptive style which is characterised by the formation of a lava dome at the top of the volcanic edifice and by associated explosions and deadly pyroclastic flows. Using techniques similar to those employed to image patients’ limbs with CAT scans, we have imaged the volcano and the rocks beneath it with unprecedented detail, providing an image of its plumbing system including the shallow magma chamber. the combination of these results, along with the large amount of geological data collected on Montserrat over the years make it one of the best studied volcanoes on Earth.

3D perspective of the islands with sections of the 3D seismic velocity model

The RRS James Cook shooting with airguns around Montserrat in december 2007

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