This statement was issued by the members of Scientific Advisory Committee (SAC) on 11 March 2009.

After three months of relatively little surface activity following the explosion of 28 July 2008, there was a period of one month of lava extrusion that was preceded by explosions on 2 December 2008 and culminating in further explosions on 3 January 2009. This new lava was extruded from a vent high on the western, Gages, side of the dome. Pyroclastic flows from this activity reached the sea at Plymouth, White River and entered the Tyer's Ghaut reaching as far as Lees. The new lava added to the dome on the western side increases the mass available to any collapse to the west or north. Since early January there has been no further lava extrusion. It appears from the current degassing and incandescence that the lava vent has become more centralised.

The July and December episodes of explosive and extrusive activity are unusual compared to the longer duration periods of extrusion and pause that we have seen in the past. They may reflect the way the volcano is responding to renewed magma rise beneath the large existing dome. The volcano may be entering a period of shorter episodes of extrusion and accompanying explosions with intervening shorter pauses. We think lava extrusion on the dome will be the most likely next development. Whilst the volcano appears to be quiet at the surface the MVO measurements of seismicity, deformation and gas indicate that the volcano remains active. Thus there is no sign of the end of the eruption yet and we estimate that the likelihood of that occurring during the next year is about 6%.

For people living in Zones A and B the risks have risen again slightly. The more frequent stop-start character of the dome growth will make the management of the risk levels more trying.

• < Prev