Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 4 July
to 4 pm 5 July 1997

The alert level system has been revised by zones

Activity at the volcano since yesterday has been at about the same level. Two low intensity periods of pyroclastic flows were observed during the reporting period at 9 pm last night and after 10.55 am this morning, the latter following an intense hybrid earthquake swarm.

Some small pyroclastic flows down Mosquito Ghaut occurred from 8 pm to 9.30 pm, and glowing clouds were observed to the north of the volcano. Overnight the volcano was relatively quiet, although a hybrid swarm started at 6.46 am and lasted until 10.03 am. This was followed by a tremor episode which built up into small pyroclastic flows. The ash cloud from this event reached approximately 15,000 feet.

The tiltmeters on Chance's Peak continue their cyclic pattern although the peak associated with the pyroclastic flow activity last night was not very well defined, and the time period between peaks is now irregular.

Seismicity has been higher today with 41 rockfall signals, 1 long period and 76 hybrid earthquakes recorded by the seismic network today. No volcano-tectonic events were recorded.

An inspection of the ghauts from the helicopter revealed that the pyroclastic flows overnight and today had run-out distances of about 0.5 km from the dome, and a helicopter survey of the deposits since 25 June was undertaken. The pyroclastic flow deposits from 1 July in Fort Ghaut near the Lovers Lane Intersection were examined on the ground, and temperatures of up to 400 degrees centigrade were measured at 45 cm depth. Several houses were badly damaged.

Measurements of the sulphur dioxide flux from the volcano were made today by helicopter using a technique flying parallel and to the side of the plume. Results from these runs are currently being processed.

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.

Dr. Brian Baptie (British Geological Survey) and Dr. Rick Hoblitt (United States Geological Survey) arrived today, and Dr. Sue Loughlin (British Geological Survey) left Montserrat today.

Montserrat Volcano Observatory