Volcano CAT scan reveals Montserrat's inner workings
29 December 2008
The detailed internal structure of an active volcano in the Caribbean has been revealed for the first time.
The Soufrière Hills volcano on Montserrat has erupted on and off since 1995 and since then has been one of the most closely monitored volcanoes in the world. After the mid 90s, eruptions from the volcano destroyed the island's capital city Plymouth and have resulted in widespread evacuations. Around two thirds of Montserrat's population have fled the island.
This is the first time scientists have surveyed the whole volcano and the rocks deep beneath it in such great detail. The findings will give researchers a much clearer understanding of how the volcano works.
Professor Stephen Sparks from the University of Bristol was part of a team of researchers to present their findings at the American Geophysical Union Fall Meeting in San Francisco in mid-December. The group also included scientists from Penn State University, the National Oceanography Centre, Southampton and Cornell University.
'Working out when the volcano will erupt can be a guessing game, but now we know so much more about the rocks beneath Soufrière Hills, we have a much better idea of the speed that earthquake waves travel through the rocks underneath this volcano,' said Sparks.
The researchers used a range of methods to investigate volcanic activity. They inserted four strain meters - which measure how the Earth's crust deforms - 200 metres beneath the flanks of the volcano, 130 seismometers on the island and ocean bottom seismometers. Using the research ship RRS James Cook, the group used seismic waves generated by underwater air-gun explosions and natural earthquakes to map inside and underneath the volcano in unprecedented detail.
'This is really exciting, because we're getting information about the whole magma transport system from the deep source to when the volcano erupts.'
Professor Stephen Sparks, University of Bristol
The results from these analyses are akin to the results of a hospital CAT scan. Ten to 30 kilometres beneath the volcano, the researchers found igneous rocks - revealed when waves bounce back and are then picked up by seismometers. They also discovered a narrow feeding channel from a deeper chamber around five kilometres underneath the volcano. The magma chamber appears to be saturated with dissolved gas. When the magma in the chamber is shaken, the gas expands, increasing the pressure in the chamber.
'This is really exciting, because we're getting information about the whole magma transport system from the deep source to when the volcano erupts,' added Sparks.
Although other groups have used the same methods to investigate volcanic structure, nobody had used them all together until now. Most researchers use remote sensing technology - satellites - to get information about the insides of active volcanoes, because it's virtually impossible to get direct measurements from the inside of volcanoes. Satellites reveal information such as uplift of the ground, volcanic temperatures and the types of gases emitted.
The Soufrière Hills volcano is a typical island arc volcano. An island arc is where two parts of the Earth's crust crash into each other. When these layers collide, the heat generated by the impact melts the rock beneath the volcano. Viscous and gaseous magma finds its way through narrow channels to the surface and severe eruptions usually follow.
The Montserrat Volcano Observatory takes detailed measurements and reports on the volcano's activity to the government and people of Montserrat.
Interesting? Spread the word using the 'share' menu on the top right.