Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 23 July
to 4 pm 24 July 1997

The alert level system has been revised by zones

Activity at the volcano continues to be dominated by rockfalls and small pyroclastic flow signals. No clear views were obtained of the summit.

A late morning observation flight indicated that the small pyroclastic flow which was observed at 6:20 am this morning had occurred in the upper parts of Tuitts Ghaut. No fresh deposits were noted in any of the other ghauts around the volcano. The scree slope of the dome now covers the Gages wall completely and rockfalls are occurring directly into the valley. Steam venting from the lower flank of the dome into the Tar River valley has decreased somewhat since this area was last observed two days ago.

Fifty-five rockfalls, three long-period events and three volcano-tectonic earthquakes were recorded by the seismic network today. The VT earthquakes were the largest recorded for the month and occurred at shallow depths beneath English's crater. Broadband tremor, which was generally of a low amplitude, was recorded for variable periods on the St George's Hill station throughout most of the period.

GPS measurements were conducted today at Lees Yard, Waterworks, Garibaldi Hill and MVO. The survey is currently being completed and the results would be given in a subsequent report. No EDM measurements were conducted today but a reconnaissance flight was carried out to help determine possible locations for new permanent target sites on the flank of the volcano.

Despite the apparent lull in seismic activity, the dome continues to grow and the potential for large pyroclastic flows onto the northern and western flanks of the volcano remains significant. There have been periods in the past when the dome has continued to grow with few earthquakes apart from rockfalls. Residents should note that pyroclastic flows and ash eruptions have occurred during the past few weeks with no direct association with seismicity. This means that people entering the designated exclusion zone put themselves at extreme risk. In addition, people in the northern and central 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.

The Belham River valley provides a pathway for mudflows which may develop rapidly following a period of prolonged rainfall. It therefore remains an area for anxiety over safety since it is also a potential pathway for pyroclastic surges. Mudflows can travel very fast and may be quite close to boiling point. In addition, they may extend much further along the river valley than the pyroclastic surges. As recent temperature measurements in the area just north of Farm's River indicate, pyroclastic flows and surges retain their high temperatures for several weeks after they were deposited. Residents are therefore urged not to approach, attempt to handle or walk on these deposits since they could sink in, due to the uncompacted nature of the deposit, and become severely burnt. Dust masks should always be worn when there is ash in the air.

Dr Keith Rowley left Montserrat after a month long tour of duty yesterday while Dr Richard Herd returned to take up duties at the MVO after a short break.

Montserrat Volcano Observatory