Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 27 May
to 16:00 28 May 1996

Volcanic activity at the Soufriere Hills volcano has been dominated during this period by continued rock avalanches from the growing lava dome which have produced several ash clouds to the west.

Seismicity has been at a moderate level throughout the period, with rock-fall signals dominating the record at all of the seismic stations. Signals were mainly at a low or moderate level, although larger signals at 16:45 on 27 May and at 05:12, 10:02 and 14:19 on 28 May were correlated with large rock fall/pyroclastic flow events which deposited hot rocks and ash in the northern part of the upper Tar River Valley down as far as the Tar River Soufriere. In addition to rock fall signals, one volcano-tectonic earthquake was recorded, located at a depth of about 0.5 km to the north of the crater, and 8 long-period and 11 hybrid events were also recorded.

Electronic Distance Meter (EDM) measurements were completed today on the northern triangle between St George's Hill, Windy Hill and Farrell's Yard; the results of the survey are still being processed. Global Positioning System (GPS) measurements are not being undertaken at present due to a technical problem which it is hoped will be solved during the week. Indications from the previous few days are that deformation of the volcano continues to be at a very slow rate, very close to the limit at which any movement can be detected using EDM and GPS techniques.

Gas measurements were today made both by COSPEC and by FTIR methods. The results of both sets of measurements are still being processed, although initial indications from the FTIR method suggests a very low Hydrogen Chloride (HCl) content in the volcanic plume. The COSPEC indicates a Sulphur Dioxide (SO2) production of about 112 tonnes per day from the volcano, similar to results from the previous several weeks.

Visual observations were made from the ground in a number of locations throughout the day and also from the helicopter in the late afternoon. No major changes in the shape or size of the dome were noted, although semi-continuous rock falls were occurring from the northeastern and eastern flanks of the dome, and some increase in rock fall activity was also noted for the northern and southwestern flanks of the dome. Several of the rock falls during the day produced light ash falls in the Amersham and Plymouth areas.

A network of ash collectors was deployed today between Gingoes and Salem; these collectors will enable better estimates of the volume of ash being produced from the volcano, which may help with estimates of dome growth rate. Analysis of the collected ash will also aid in developing a better understanding of the volcanic system.

Dr Rosalyn Lopez, Jet Propulsion Laboratory, Dr Haruldur Sigurdsson, University of Rhode Island, Professor Wagner, University of Geneva, and Dr Laurent Stieltjes, BRGM, France, all departed Montserrat yesterday afternoon after brief visits.

The present level of activity at the Soufriere Hills Volcano continues to cause concern to the scientists. The MVO urges that visits to the evacuated zone are kept to a minimum. The Tar River, Long Ground and Whites areas are extremely dangerous and should not be entered under any circumstances.

Montserrat Volcano Observatory