It seemed like events at Soufriere Hills had been heading for a dome collapse for the past few week and sure enough, part of the summit dome collapsed last night, producing pyroclastic flows that reached the ocean along with a 40,000 foot ash column. The report I received from the Montserrat Volcano Observatory offered the following details:
The collapse started at 11:27 pm local time on Monday 28th July 2008 without any precursory activity. Part of the western side of the lava dome collapsed generating pyroclastic flows that reached Plymouth and the sea.
There were also a few explosions from the dome during the collapse, with
the largest at approximately 11:32 pm.
The height of the ash column was estimated at 12 kilometres (40,000
feet) above sea level.
Luckily, unlike the eruption in 1997 that killed 17 people, there were no reported fatalities or injuries related to this dome collapse event. The dome collapse itself is merely the failure of the oversteepened lava dome at the summit of Soufriere Hills but the avalanche becomes a pyroclastic flows because the material in the dome is still hot and mixes with whatever volcanic gases and ash are being expelled from the vent as well. This is the modus operandi of Soufriere Hills - at least in the last 10 years of eruptions at the Caribbean volcano.