The Preliminary Statement of the Scientific Advisory Committee has been released.
The volcano has had a quiet six months since our last report. There was no extrusion of new lava and no explosions in this period. Surface activity was restricted to rockfalls and occasional small pyroclastic flows from the dome, together with mudflows. Heavy rains in May 2009 caused substantial erosion of gulleys on the higher slopes and deposition of mudflow deposits in the lower ghauts. There is no evidence from either seismicity or visual observations that the dome was recently intruded or strained internally such that its stability has changed.
The MVO team has made excellent progress over the last six months in re-instating some volcano monitoring systems, which had deteriorated following the loss of helicopter support. MVO measurements of deformation show that the volcano has continued to inflate since mid-2007, apart from a brief deflation during the December 2008 period of lava extrusion. Gas continues to be released at rates similar to those seen throughout the eruption. These sets of measurements show that the volcanic system remains active. However, the number of earthquakes recorded has fallen to the lowest level we have seen during the eruption. This, together with the pattern of shorter duration extrusion events seen in the last 18 months, suggests that the long-term behaviour may have changed. One interpretation of this is that it hints at a possible ΓÇ£beginning of the endΓÇ¥ of the eruption, though all the formal end-of-eruption criteria are not yet met.
In terms of the risks faced over the year ahead, however, the levels in zones A, B and C have changed very little from our last risk assessment. As was seen in December last year, sudden resumption of explosive and extrusive activity can rapidly pose a threat to the areas around the Belham valley.