Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 6 July
to 4 pm 7 July 1997

The alert level system has been revised by zones

Activity at the volcano has been at about the same level as yesterday with rockfalls and hybrid earthquake swarms being the main phenomena recorded by the seismic network.

Two hybrid earthquake swarms have occurred during this period. The first began at 11:00 pm last night and continued until about 2:30 am this morning; the second began at 2 pm and is still continuing at the time of reporting. Otherwise there is little seismic activity apart from small rockfall signals.

The tiltmeter on Chance's Peak continued its cyclic pattern with another peak experienced at about 2:00 am last night. At the time of reporting, the tiltmeter is approaching its peak again. Therefore the time period between peaks seems to be increasing. No pyroclastic flow activity has been observed today.

40 rockfall signals, 43 hybrid and 2 long period earthquakes were recorded by the seismic network today which is about the same number as yesterday. No volcano-tectonic events were recorded.

Further GPS measurements were conducted on the new deformation network which was established with stations at Garibaldi Hill, Lees Yard, MVO and the Waterworks. The line between Waterworks and Lees Yard was also successfully surveyed by the EDM.

The dome was clearly visible for a short time early this afternoon. Photographs were taken from Whites to ascertain the current volume of the dome. Views from the helicopter showed that the area of growth above Mosquito Ghaut now appears as a steep continuous face, and the area above Gages valley also appears to have grown. On the eastern face of the dome, there is vigorous steaming which seems to be controlled by radial fractures in the dome. The summit area of the dome is now very broad and flat with the maximum height approximately corresponding to the height of Chances Peak.

It seems likely that the cyclic nature of the activity will continue with repeated periods of pyroclastic flows giving rise to ash clouds away from the volcano, and thus people in the safe zones should stay alert and listen to Radio Montserrat. The current area of activity in the crater makes Mosquito Ghaut and Gages the most likely pathways for pyroclastic flows, but further flows in Tuitt's, Tar River or White River are possible as well. Access to Plymouth is completely restricted.

The Belham River valley is also an area for anxiety over safety. It may provide a pathway for further pyroclastic surges and there is also a risk of hot mudflows which may form rapidly if there is a period of heavy rain. Mudflows travel extremely fast and may be near boiling point, they may extend much further along the Belham River valley than the pyroclastic surges. The pyroclastic flow and surge deposits will remain extremely hot for several days. Residents must not approach, attempt to handle or walk on the deposits because of the risk of severe burning. Residents and workers are also reminded to wear a dust mask when there is ash in the air.

Wilkie Balgobin (Seismic Research Unit) left Montserrat today after a month on the island.

Montserrat Volcano Observatory