Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 9 July
to 4 pm 10 July 1997

The alert level system has been revised by zones

Visible activity at the volcano has continued at about the same level as yesterday. The seismicity is dominated by rockfalls. A few small pyroclastic flows have occurred in the Gages valley.

The amplitude of the cycles defined by the Chances Peak tilt station has continued to decline and is now almost down to background level. Two cycles were recorded during the period, one peaking at about 7:00 pm yesterday and the other at midday today. No hybrid earthquakes or tremor were associated with any of these cycles. Three small pyroclastic flows, at 10:33, 11:30 and 11:55 am today, occurred during the very low amplitude peak in the second tilt cycle. This flow did not reach further than the Lower Gages Soufriere.

Strong glowing over Mosquito Ghaut and Gage Ghaut were observed from the MVO at 8:00 pm last night. A strong seismic signal produced by an ash eruption occurred at 9:46. This occurred during a trough in the Chances Peak tilt cycle. The elevation of the plume generated was undetermined. Several ash clouds were produced by large rockfalls during the period from 14:54 to 16:42.

Observation flights made with the helicopter during the morning indicate that the road at the base of the Galways Soufriere has begun to undergo further mass movement. This is not felt to be directly related to the volcano but due to normal mass wasting processes which operate on the flanks of the volcano. Recent heavy rainfall and the already weakened state of the rocks in this area has in the past produced landslides and road slippage.

72 rockfall signals and 2 hybrid earthquake were the only signals recorded by the seismic network today. There were no volcano-tectonic or long period earthquake recorded.

The EDM line between Waterworks and Lees Yard was surveyed today. Another occupation of new GPS stations at the Waterworks, MVO, Garibaldi Hill and Lees Yard was also conducted today. The data collected from these stations is still insufficient for any clear trends to be defined.

The cyclic pattern which has been defined at the volcano during the past few weeks appear to be changing. Pyroclastic flow and ash eruptions have occurred during the past two days with no preceding increase in seismicity or direct association with the tilt cycle. This means that people entering the designated none exclusion zone put themselves at extreme risk. 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 valley the most likely pathways for pyroclastic flows, but further flows in Tuitt's, Tar River or White River are possible as well.

Plymouth is particularly vulnerable since pyroclastic flows have begun to enter the Gages valley without warning and have the potential to reach the coast. Persons entering these areas place themselves in extreme danger.

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.

Montserrat Volcano Observatory