The partial collapse of the dome in the volcano's crater also unleashed flows of hot gas and rocks, triggering sirens for the evacuation of about 20 people from a nearby village.
Paul Cole, director of the Montserrat Volcano Observatory, said it appeared to be the most material ejected by the volcano in about four years. He estimated 10 percent to 15 percent of the hardened lava dome had collapsed.
"When we're looking at the lava dome now, there's a large scoop out of it that's missing," Cole said. The dome has crumbled several times since the volcano became active in 1995, and Cole said it is possible activity will settle down as the dome builds itself up again. He said there is no immediate cause for concern about more dangerous eruptions.
The 1997 eruption killed 19 people and buried much of the island, including its former capital, Plymouth, which is now abandoned. Half the British territory's 12,000 inhabitants left.