Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 30 July
to 4 pm 31 July 1997

The alert level system has been revised by zones

Activity at the volcano has been elevated since about 3 am this morning. The seismometers were showing high amplitude tremor for much of the day and this was associated with convecting ash clouds to 20,000 feet.

133 rockfalls, 35 long period events and one hybrid earthquake were recorded today. 14 of the long period events triggered rockfalls. This is about the same number of rockfalls as yesterday, but since 3 am this morning there have periods of continuous high amplitude tremor on the Lees Yard station. Initially this was thought to be due to pyroclastic flows. However, views of the flanks of the volcano from the helicopter late this morning and early evening showed that there were very few new deposits. A few small flow lobes could be seen in Tuitts Ghaut to about 2 km from the dome and there were new deposits in Gages valley as far as Gages village. No new deposits could be seen in the Tar River, Mosquito Ghaut or over Galway's wall.

There has been a significant increase in long period earthquakes. Similar increases have occurred before periods of major pyroclastic flow activity earlier in the eruption of the Soufriere Hills volcano.

Many ash plumes were produced throughout the day and the most vigorously convecting clouds reached above 15,000 feet. Early in the morning, these drifted to the north and north-west in light winds, but later in the day the ash clouds travelled mostly to the west. Early in the morning there were reports of small explosive sounds from the volcano, and this was confirmed by an analysis of the seismic signals on the broad band system.

Several more intense periods of activity have occurred throughout the day, most notably between 12.30 pm and 2.30 pm. At this time, the signal from the new Lees Yard seismometer was recording a near maximum amplitude signal for about 2 hours, but only one moderate sized pyroclastic flow was observed during the period. Ash plumes were generated in pulses every few minutes, and many of them were vigorously convecting. It appears that most of the ash generation has originated from near the top of Gages wall and is not necessarily associated with pyroclastic flows.

Residents should note that pyroclastic flows and ash eruptions have occurred with no direct association with seismicity. 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.

Montserrat Volcano Observatory