Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 12 April
to 16:00 13 April 1997
The current alert level is ORANGE

Activity has been at a low level for most of the day. A small earthquake swarm occurred this morning. Further rockfalls have been occurring during today through the enlarged canyon in the Galway's Wall.

The main seismic activity today was a small swarm of hybrid earthquakes which lasted from 5:56 am to 8:48 am. Only nineteen (19) events were triggered during this swarm. There was one (1) volcano-tectonic earthquake, one (1) long-period earthquake and 25 rockfalls. Two regional tectonic events were recorded by the seismic network at 10:46 pm last night and 6:33 am this morning. Preliminary examination of the records of these events indicates that the earthquake was located somewhere to the north of Montserrat.

Today the earthquake counts come from the broadband seismic network, and the results from the broadband network will be used in future reports. This network was installed in October last year, and since then it has been running along side the existing seismic stations since then. The new network is a major step forward in the seismic monitoring of the volcano, and will allow more information to be gathered about the processes occurring within the volcano. The broadband network is slightly more sensitive, and so records more earthquakes than the old network.

Low amplitude tremor has been intermittently recorded on the Gages seismometer throughout the day. Slightly elevated tremor was also recorded on the Windy Hill and St. Patrick's seismometers between 2:00 pm and the end of the reporting period. This has since died away.

Visual observations were limited today by low cloud. Some of today's rockfalls produced ash clouds which were blown over the southern parts of Plymouth. The airport control tower reported seeing two rockfalls just before 3:00pm this afternoon. These originated on the northern flank of the dome. A field team was despatched to Whites for further observations. No further events have occurred in this area.

A team began an appraisal of mudflow hazards in the Plymouth area in preparation for the coming hurricane season. Information will be provided for the Authorities regarding the possible hazards from mudflows.

No GPS or EDM surveys were carried out today.

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.

Montserrat Volcano Observatory