Volcano's Activity May Be Predictable, Second Study Suggests
Washington D.C. - A group of researchers from the UK have determined that the volcanic ash blanketing the Caribbean island of Montserrat may pose a serious health risk to people who have been exposed to it. The ash, which the Soufriere Hills volcano has ejected in large plumes since 1995, has a surprisingly high concentration of a mineral known as cristobalite that can cause the lung disease silicosis. In a second study, another US and UK team has determined that it may be possible to predict short-term activity of the volcano. Together, the two studies, which appear in the 19 February issue of Science, provide information that may help to reduce the risks associated with living close to an active volcano.
The violent eruptions on Montserrat have necessitated the evacuation of the southern part of the island. Many of Montserrat's inhabitants are waiting things out in the north, but even there, as the first UK study suggests, they may not have escaped all of the volcano's effects.
A team of researchers led by Peter Baxter of the University of Cambridge analyzed the ash and found that it contained harmful levels of very small grains of the silica mineral cristobalite. When inhaled over long periods of time, or possibly in large amounts, this mineral has been known to cause silicosis, a lung disease that is typically considered a hazard for workers in occupations such as quartz mining, stone cutting, blasting, and tunnel construction. Silicosis occurs when tiny particles of crystalline silica-small enough to reach the smallest air passages and air sacs, or "alveoli"-become embedded in the lungs. As these particles accumulate they cause thickening and scarring of the tissue, and eventually the lungs cannot efficiently supply oxygen to the blood. Because these effects develop over a long period of time, it is not yet clear what the effects of the exposures at Montserrat may ultimately be.
Ash has been produced in two different types of eruptions from the Soufriere Hills volcano. In the first, magma erupts from the interior of the volcano, both violently and as thick, sluggish lava that builds up into a giant dome in the volcano's crater. Periodically, when the dome's sides become too steep, it collapses, also resulting in violent (and more frequent) eruptions.
After the Soufriere Hills volcano sprang to life about three and a half years ago, generating long-lived eruptions and persistent ashfall, Baxter wondered whether the ash might contain harmful amounts of cristobalite. He gathered a team of researchers, whose fields varied from occupational health to mineralogy and volcanology, to investigate this possibility. The researchers found surprisingly high levels of harmful cristobalite particles in the ash from the lava dome eruptions. These levels were two to five times higher than were found in ash from the volcano's interior, indicating that the cristobalite crystals were growing inside the lava dome between eruptions and were further concentrated in ash eruptions. Thus, volcanoes with lava domes may pose a greater risk for silicosis than other types of volcanoes.
To further investigate this risk, the authors monitored human exposure and found that human activity made a significant contribution to the levels of harmful particles in the air. Initially the ash drops in clusters, the way falling snowflakes often clump together, but it appears that activities such as driving, sweeping, or children's schoolyard games break apart the clusters on the ground and re-suspend the tiny particles in the air. "The period after the eruption might not seem like the most dangerous, especially because you can't actually see the ash suspended in the air," said Stephen Sparks of Bristol University, who was a member of Baxter's research team. "But it does hang around for quite a long time."
More work is necessary to understand the specific health effects of inhaling the volcanic ash. For example, researchers must still determine acceptable levels of exposure to the ash and the effects of short-term exposure. "Our results suggest all sorts of avenues for further research," said Sparks.
In a second paper in the same issue of Science, Barry Voight of Pennsylvania State University and colleagues at the Montserrat Volcano Observatory describe the cyclic behavior of the Soufriere Hills volcano, which should make it easier to forecast volcanic activity in the short term (as opposed to over decades or centuries) and thus improve efforts to minimize the damage caused by eruptions.
As the lava dome grew between 1996 and 1998, the authors carefully kept track of the repetitive cycles of earthquakes, changes in steepness of the dome walls, degassing, and explosive eruptions. Using this information, they constructed a model for how the cycles work. First a plug of more solid magma forms in the uppermost conduits of the lava dome's inner plumbing. Pressure then builds inside the dome, causing it to inflate and generating a flurry of earthquakes. Once the pressure has increased past a certain point, the plug is expelled and gas escapes. Finally, a new batch of fresh magma rises to replace the plug and the process begins again.
Understanding this process should help researchers to better interpret information they collect from monitoring lava dome volcanoes such as Soufriere Hills, which could lead to improved forecasts of the timing and eruptive style of volcanic activity.
ORDER ARTICLE #9: "Cristobalite in Volcanic Ash of the Soufriere Hills Volcano, Montserrat, British West Indies," by P. J. Baxter at U. of Cambridge in Cambridge, UK; C. Bonadonna, S. C. Kohn, M. D. Murphy, R. S. J. Sparks at Bristol U. in Bristol, UK; R. Dupree at U. of Warwick in Coventry, UK; V. L. Hards, R. A. Nicholson, G. Norton, B. P. Vickers at British Geological Survey in Nottingham, UK; A. Nichols, A. Searl at Institute of Occupational Medicine in Edinburgh, UK. CONTACT: Stephen Sparks at 44-79545419 (phone), 44-79253385 (fax), or steve.sparks@bristol.ac.uk (e-mail)
ORDER ARTICLE #8: "Magma Flow Instability and Cyclic Activity at Soufriere Hills Volcano, Montserrat, British West Indies," by B. Voight, R. S. J. Sparks, A. D. Miller, R. C. Stewart, R. P. Hoblitt, A. Clarke, J. Ewart, W. Aspinall, B. Baptie, T. H. Druitt, R. Herd, P. Jackson, A. M. Lejeune, A. B. Lockhart, S. C. Loughlin, R. Luckett, L. Lynch, G. E. Norton, R. Robertson, I. M. Watson and S. R. Young at Montserrat Volcano Observatory in Montserrat, British West Indies. CONTACT: Barry Voight at , 814-863-7823 (fax), or voight@ems.psu.edu (e-mail)
For copies of these article please email scipak@aaas.org, call 202-326-6440, or fax the form below to 202-789-0455.
For images of the Soufriere Hills volcano, please contact Andrea Messer, Pennsylvania State University Communications Office at 814-865-9481 (phone), 814-865-9421 (fax) or aem1@psu.edu (e-mail).
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