Extended exposure to volcanic ash particles is proving a serious health hazard. Last year, researchers studying health effects after Montserrat’s Soufriere Hills volcanic eruption July 18, 1995, linked the ash to lung disease. But the andesitic lava dome’s extrusion has not settled down.  Pyroclastic flows and large ash plumes continue to harm residents.

The hidden hazards that one is exposed to in these volcanic eruptions have long-term health effects, says Steve Sparks of Bristol University. The greatest risk comes from volcanic ash containing significant amounts of cristobalite and other particles less than three microns in diameter.  Inhaling these particles allows for deposition deep in the lung.  Large amounts of cristobalite can cause silicosis, a permanent scarring disease of the lung.

Peter Baxter, a professor at the University of Cambridge and co-author of the paper, realized that ash was a concern because of the health issues associated with the 1980 eruption of Mount St. Helens.   Researchers established that ash from the Mount St. Helens eruption contained cristobalite but concluded that since the eruption was relatively brief, it did not pose a serious long-term health risk.
 

“It’s a very novel situation on Montserrat where a community is exposed to dusty conditions from a volcano for years,” Baxter says. “In addition, the lava dome in this volcano is producing extra cristobalite in the hot dome itself.” The researchers found that human activity was a main factor in contributing to the extent of exposure to the very fine, potentially harmful particles. “One of the initial findings suggested that ash stays on the ground for weeks if not months,” Sparks says.  And human activity can disturb the ash, break it up and resuspend it — allowing fine particles to concentrate in greater amounts than what was originally erupted.

Above:  A dense ash cloud moves downwind from the Soufriere Hills volcano, Montserrat, early 1997. Right:  Vigorous ash venting followed an explosion at Montserrat's Soufriere Hills volcano in October 1997. The wind is moving the ash cloud over western Montserrat and pyroclastic flow deposits can be seen on the flanks of the volcano.  Photos courtesy of Simon Young, Montserrat Volcano Observatory.

An andesitic lava dome grows very slowly, permitting the gradual formation of cristobalite.  Pryoclastic flows containing this crystalline silica polymorph form when an unstable part of the dome collapses.  Initially cemented, this material becomes a serious health hazard after people intervene by hitting clumps of material with their cars, for example, and crushing it into very fine particles humans can inhale.

Relative to more explosive eruptions, dome volcano eruptions also increase the possibility that the inhaled dust is more harmful. The dome’s collapse crushes pyroclastic material into ash. This not only makes more particles of inhalable size, but the percentage of harmful particles like silica and glass in fine ash is greater than in material not affected by the eruption.  “Because they are small and weak, they get selectively crushed. Dust that you breathe in has 20 percent more [harmful particles] than what is on the ground,” Sparks says.

The researchers — including scientists from the University of Warwick, the British Geoloigcal Survey and the Institute of Occupational Medicine in Edinburgh — found that ash concentrations regularly exceeded the United Kingdom’s air quality standard for areas of frequent ashfall.

To prevent adverse health effects, scientists told people living near the Soufriere Hills volcano that masks, which filter out most of the dust, are the best defense.

“We monitor the ash situation all the time to ensure that the islanders keep out of trouble, especially children,” Baxter says.  “Not all the workers take advice about masks, and we have concerns about some of them for the future if ash falls continue.”

Julia Cole
Geotimes contributing writer