Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 11 April
to 16:00 12 April 1997
The current alert level is ORANGE

Activity has been at a much lower level today than it was yesterday. A swarm of hybrid earthquakes occurred during the early morning and some rockfalls have been occurring during today through the enlarged canyon in the Galway's Wall.

Seismic activity during the period under review was dominated by a swarm of hybrid earthquakes which started at about 2.30 am this morning and lasted until about 9.15 am. Two additional, large hybrid earthquakes occurred this afternoon. In total, 44 hybrids were recorded during the 24 hour period. One volcano-tectonic and two long period earthquakes were also recorded. Rockfall activity was at a relatively low level overnight following yesterday's collapse, but has picked up somewhat during today. A total of 33 rockfall signals were registered by the broadband seismological network, 6 of which were preceded by long period signals possibly related to gas release triggering the rockfalls.

Low amplitude tremor best recorded on the Gages seismic station was associated with an increase in gas emissions in the late morning and early afternoon. Vigorous degassing with a well-defined plume 500 to 1,000 feet above the dome and moving westwards was observed at this time. This plume could be traced more than 75 km downwind by weather satellites.

Visual observations were limited today by low cloud, although further observations of the new collapse scar indicated that it is of similar size to that created during the Easter Sunday collapse. Although the chute in Galway's Wall was not deepened yesterday, it does appear to be somewhat wider and is already re-filling with debris by way of rockfalls. Some of these rockfalls produced ash clouds which were blown over the southern parts of Plymouth.

Collection of ash and water samples was undertaken today. The thickness of ash deposited on land over southwestern parts of Montserrat from yesterday's activity was quite small, with most ash being carried out to sea by the wind.

No GPS or EDM surveys were carried out today. COSPEC measurements will not be made over the next 10 days or so due to the instrument being off-island; it is accompanying Mr Billy Darroux to a gas workshop in Arizona, where it will be calibrated and tested to ensure accuracy of measurements. Yesterday's measurements gave a sulphur dioxide emission rate of more than 1500 tonnes per day. This follows the normal trend of high emissions following collapses. An interesting feature of the gas plume was that there were two distinct components, related to degassing from the collapse scar and from the pyroclastic flow deposits themselves.

The alert level remains at ORANGE and pyroclastic flows could occur without warning in both the Tar River and White River valleys, and surrounding areas remain extremely dangerous. Activity could escalate quickly, and visits to zone C should be kept brief. Zone D should not be occupied again tonight.

Dr Ricky Herd left Montserrat this afternoon for a well-earned break. Dr Willy Aspinall is making a brief visit to MVO. Mr Billy Darroux departed for Arizona today to the workshop mentioned above.

Montserrat Volcano Observatory