Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 14 June
to 4 pm 15 June 1997
The current alert level is ORANGE

Overnight activity produced significant changes in the upper Mosquito Ghaut, and some material appears to have spilled over the crater rim above Gage's. An upsurge in pyroclastic flow and rockfall activity took place later in the day with production focused in the Mosquito Ghaut and, to a lesser extent, down the south side of the Tar River Valley. Very little material entered Tuitt's Ghaut during the present episode.

The level of rockfall and pyroclastic flow activity was low at 4pm yesterday afternoon and but began to increase by 6pm. There was then a series of moderate rockfalls and small pyroclastic flows which peaked in activity about 10pm followed by a decline back to low level activity by about 1am this morning. Other than the rockfall and flow signals, the level of seismic activity was relatively low overnight with only a few small long period events.

An inspection of the volcano from the helicopter this morning revealed that there had been significant changes to the top of Mosquito Ghaut overnight. Dome material had cut a small chute through the top of the crater rim and pyroclastic flow material had advanced about 500m down the ghaut. In addition, part of the righthand (western) wall of the ghaut had been undercut and had slipped, and some of the opposite wall had also been eroded, enlarging the opening below the dome. There has not been any significant rainfall in recent days so these changes have been caused by volcanic action. A small amount of new material appeared to have gone over the Gage's crater rim also. The top of the dome, which comprises small spines and large blocks, was producing continuous steam and ash. It has several very steep faces and appears unstable.

Rockfall and pyroclastic flow activity on the dome increased markedly just before noon and was still at an elevated level at the end of this reporting period. The activity predominantly involved pyroclastic flows into Mosquito Ghaut which, at times, were being generated nearly continuously, with less frequent but moderate pyroclastic flows down the south side of the Tar River valley. Another inspection of the deposits will be made shortly to ascertain how far the most recent flows have advanced.

There were five significant long period earthquakes today, and seven hybrid earthquakes, both numbers being down on the levels of a day or two ago. However, the number of rockfall signals increased to 165, reflecting the elevated level of activity on the dome.

More COSPEC runs were made today to measure the amount of sulphur dioxide being expelled from the volcano. These and other recent sets of measurements will be processed and reported shortly.

Further pyroclastic flow and rockfall activity can expected down Mosquito Ghaut and the Tar River valley, and may become reactivated down Tuitt's Ghaut. Although today's pyroclastic flows have been relatively small, larger pyroclastic flows could occur without warning and might affect the road above Harris's and along the section past Farrell's Yard. Pyroclastic flows and surges are hot and travel extremely fast, they cannot be outrun. Zones A and B on the risk map should not be visited. WH Bramble airport remains operational, although the public are reminded it is open for essential travel purposes only: people not travelling should not visit the airport.

Montserrat Volcano Observatory