Soufriere Hills volcano (Montserrat): phreatic explosions suggest rising magma

New ash eruptions have occurred at Soufriere Hills volcano on Montserrat. The activity is probably phreatic in origin and caused by rising magma under the volcano.
The ash emissions began at around 8 am local time on 23 March, following 2 volcanic earthquake swarms on 22 and 23 March, the Montserrat Volcano Observatory (MVO) reports.

The vents of the new activity are on the floor of the 11 February 2010 collapse scar, immediately south of the old English's crater wall and to the west of the long-lived hottest fumarole previously identified. Fumarolic activity on the volcano increased markedly and a new steam fumarole was discovered on the NW side of the dome immediately behind Gages Mountain.
The ash venting was pulsating and produced ash clouds reaching approx. 6000 feet above sea level (3000 feet above the volcano). At its peak, black jets of ash were seen rising a few hundred meters above the floor of the collapse scar. This type of activity is probably "phreatic" in origin, caused when superheated rock meets groundwater, which evaporates explosively and fragments rock into ash.

The volcano-tectonic earthquakes are related to fracturing rocks underneath, probably as a result of increases in pressure. It is likely that these pressure increases and the resulting earthquakes, along with the rising temperature driving the phreatic activity, are related to uprising magma below the volcano. Similar types of activity have occurred at Soufriere Hills Volcano up to several months prior to restarts in magma extrusion, for example in 2005 and 2008.