Montserrat Soufriere Hills Volcano Report

Preliminary statement issued by the Scientific Advisory Committee
August 31, 2006
 

It is now just over a year since the third episode of lava dome growth began. The main event during this period was the collapse of the dome on 20 May 2006. This event removed the whole dome that had grown since August 2005 and most of the remnants of the 2003 dome within the crater, including the one that stood above Gage’s valley. A volume of about 100 million cubic metres of lava was removed, which is about half that involved in the 12 July 2003 collapse, but still makes this the second largest collapse of the whole eruption. The explosions that accompanied the collapse sent ash to a height of 20 kilometres, the highest so far recorded for Soufriere Hills.

Lava began to form a new dome within hours of the collapse on 20 May 2006 at a high extrusion rate of about ten cubic metres per second. This rate subsequently declined and in August has been at a rate of about five cubic metres per second. The dome has been growing rapidly such that it’s top is now about 900 metres above sea level and has a volume of about 55 million cubic metres, similar in size to that of March 2006. There have been a few minor collapse events since, such as on 30 June and 29 August.

If the rapid rate of growth continues, without major collapse, then the dome will reach a sufficient size to overtop the crater rim within a few months. If the direction of dome lobe growth at that time is to the north or west then small dome collapse events sending pyroclastic flows into the Gage’s or Tyer’s Ghauts will become a possibility once again. However, the 20 May collapse event and its aftermath leads us to believe that the likelihood of future wholesale dome collapses down the Tar River Valley has increased. Such collapses would have the effect of temporarily removing the pyroclastic flow hazard to the north and west, as after 20 May.

We do not yet see any changes in the nature of the lava being extruded in this third episode compared to earlier episodes. The long-term deformation of the ground around the volcano suggests that the way magma is leaving the deep reservoir is the same as seen in the second episode of dome growth. These two observations indicate that the supply of magma continues as it has throughout the eruption. We still see no sign of the end of the eruption, but we also see nothing to indicate that the eruption could generate explosions very much  larger than before.

A full report of the hazards and detailed risk assessment for a year ahead will follow. 

Contact: Government House
Brades
Tel. no. 664-491-2688