Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 31 July
to 4 pm 1 August 1997

Activity at the volcano has remained at an elevated level since 3 am on 31st August. There have been several periods of intense rockfalls and pyroclastic flow activity and hybrid swarms have restarted. Weakly convecting ash plumes have been produced throughout the period depositing ash on areas to the west of the volcano.

The period of elevated seismicity which began at 3 am on 31st July has continued with the number of long period and hybrid earthquakes being significantly greater during the past two days. 72 rockfalls, 91 long period events, 63 hybrids and one volcano-tectonic earthquake were recorded during the day. 61 of the long period events triggered rockfalls. Most of the hybrid earthquakes occurred in a single swarm which began at 5:30 am on 1st August and lasted for about 2 hours. During the peak of the swarm the frequency of events were about one per minute.

Several more intense periods of activity have occurred throughout the period, most notably between 4:39 pm and 6:00 pm and 10:00 to 11:00 pm yesterday. There were a few less intense periods of activity today but these were generally of a shorter duration and lower intensity. During these periods, high amplitude tremor saturated the seismic stations at Lees Yard and St George's Hill. In addition, ash plumes were generated in pulses every few minutes, many of which were only weakly convecting. Most of the ash generation continues to originate from near the top of Gages wall and were not necessarily associated with pyroclastic flows. Most of the plumes drifted towards the west of the volcano.

A late evening observation flight today indicated that there were no new deposits in Mosquito Ghaut, Tuitts Ghaut, the Tar River valley or Galways. There have been new pyroclastic flows into the Gages valley which extended to just below the Lower Soufriere. Flow deposits have over spilled into Gages village with two block rich lobes extending into Glen Mohr and areas just to the north of the Gages valley. The north side of the Ghaut in this area is now completed filled. A small amphitheatre appear to have been created at the top of the Gages valley due to pyroclastic flow activity during the past two days.

The tiltmeter at Chances Peak which had stopped transmitting data two weeks ago is again operational. During the past two days of elevated activity a cyclical pattern, with peaks at about 10 hour intervals, has again developed on the tiltmeter. The first cycle coincided with the elevated period of activity yesterday while the second peaked at about the time that the hybrid swarm was recorded today. The pattern currently defined by the tiltmeter is quite similar to previous patterns experienced during similar periods of activity at the volcano.

Residents should note that pyroclastic flows and ash eruptions have increased during the past 48 hours. This means that people entering the designated exclusion zone put themselves at extreme risk. People in the northern and central zones should stay on increased alert and listen to Radio Montserrat which will be on air throughout the night. This is particularly important today as the activity may increase again with no warning.

The new ash from the eruption today is still in the air in the west of Montserrat and therefore dust masks should always be worn in these areas. Drivers should also be considerate whilst driving in ashy conditions.

Professor Barry Voight of Penn State University arrived on Montserrat today for a brief visit to the MVO.

Montserrat Volcano Observatory