Eruption on Montserrat gaining strength.

A 5-day-long series of explosive eruptions assaulted the tiny Caribbean island of Montserrat last week, piling more misery on an already embattled population. The recent outbursts marked the strongest activity to date in a volcanic crisis that has dragged on for 2 years.

"The recent increase in explosions obviously raises the level of concern over where this eruption is going to go in the future," says Willy Aspinall, a scientist with the British Geological Survey who worked at the Montserrat Volcano Observatory this summer.

The Soufriere Hills Volcano in the southern region of Montserrat, a British territory, came to life with several small eruptions in July 1995 and has since grown gradually more violent. Authorities on the island eventually evacuated the capital, Plymouth, and other cities in the south. On June 25, 1997, the volcano claimed its first victims, at least 10 people who had ventured into the evacuated zone and were engulfed by pyroclastic flows--superheated gas and ash that can exceed speeds of 100 kilometers per hour.

Margaret Mangan, a volcanologist with the U.S. Geological Survey in Hawaii, was working at the Montserrat Volcano Observatory at the time. "I think that people just had no idea of the type of fury that can come down the mountain. For many folks, June 25 was really an awakening to the dangers. In the past, my sense was that it was considered a nuisance, a pain in the neck, but not necessarily a personal threat. After the 25th, it became a lot more real and a lot more frightening for people."

Scientists are monitoring the volcano from a command center set up a few kilometers northwest of the volcano. Seismometers provide some warning of impending eruptions by picking up the tremors produced as molten rock rises through the volcano. Recent eruptions have destroyed the tiltmeters that had been gauging how much the mountain swells and deforms. The observatory is staffed by a rotating cast of researchers from the University of the West Indies in Trinidad and from the British Geological Survey. Several scientists from the USGS have also served at the observatory throughout the last 2 years.

The mountain's unrest increased this summer, with periods of explosive eruptions in early July and again in early August that destroyed Plymouth. The series of blasts last week came like clockwork almost every 10 to 12 hours, occasionally showering rocks and ash onto the northern end of the island where Montserrat's remaining residents have sought refuge. Before the eruptions, the island had a population of more than 11,000 people. Scientists estimate that 7,000 of them have left.

A central mountain provides some protection for the northern end of Montserrat, but the events of recent weeks are causing authorities to reassess residents' safety, says Richard P. Hoblitt of the USGS in Vancouver, Wash., who has served at the Montserrat observatory.

"The shift to more explosive behavior has raised the concern that this thing could have a much larger event that could endanger greater parts of the island," he says. "People are getting increasingly pushed farther and farther into the north into less commodious circumstances. It's a small island to be living with an active volcano."