Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 3 July
to 4 pm 4 July 1997

The alert level system has been revised by zones

A new risk map for Montserrat came into force today, having been accepted by the Government of Montserrat. Copies of the map will be circulated to the public, and explanations given in forthcoming broadcasts and presentations. As a consequence of the activity of 25th June, the new map is divided into three broad areas each with its own individual alert level.

Volcanic activity has been slightly reduced today with a continuation of the cyclic pattern, although the regular changes in tilt at Chance's Peak have been less clear today.

Activity at the volcano increased gradually after 4pm yesterday, and a prolonged, large ash eruption started slowly at about 6.30 pm (at about the same time as on the previous two days). This episode lasted just over an hour and produced a very large ash cloud which rose to over 35,000ft. There was a small pyroclastic flow into the top of Fort Ghaut at the start of the activity, and then further flows into Mosquito Ghaut. As far as could be seen in the failing light, the latter flows appeared to reach as far as Paradise River.

The remainder of the night was quiet. At dawn, there was some heavy rain and the mountain was in cloud. There was a sudden eruption from the volcano at 07:11am this morning, starting with a explosion, heard clearly at the observatory. Pyroclastic flows were generated in both Fort Ghaut and Mosquito Ghaut, and the ash cloud rose to over 30,000ft, accompanied by some thunder. The whole event was over in about 10 minutes. This event occurred at the appropriate point in the tilt cycle, but since then eruptive activity has been very minor.

Seismicity has been relatively low today: in total, there were 34 rockfall signals, 1 long period and 15 hybrid earthquakes were recorded by the seismic network today. No volcano-tectonic events were recorded.

Two new GPS stations were established today at Lee's Yard and Garibaldi Hill to monitor deformation of the northern part of the volcanic edifice. These replace stations lost during the big eruption last Wednesday.

An inspection of the ghauts from the helicopter revealed that recent moderate pyroclastic flows are filling the upper parts of Mosquito Ghaut and Fort Ghaut, in such a way that these valleys will provide less control on the route of any future pyroclastic flows and surges.

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.

Mr Richie Robertson arrived on the island today to resume responsibility as Chief Scientist in Post; Mr Lutchman Pollard of the SRU left after a five week tour of duty.

Montserrat Volcano Observatory