Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 on 26 March 1996
to 16:00 on 27 March 1996

At around 06:42 this morning, a series of rockfalls on the eastern flank of the dome occurred, and caused a large ash plume which reached a height of 6000 ft and drifted over Plymouth and the surrounding areas. A second, smaller event occurred at 07:00. Ash from the first event was channeled down the Hot River Ghaut, for about 1 km from the dome, and ignited dead trees. Bigger rock fragments were deposited within a small area much closer to the base of the dome. These rockfalls started from near the base of the tallest spine, to the northwest of Castle Peak, which has grown over the last few days. There is no evidence that either event had an explosive component.

The nature of the signals recorded by the seismic stations suggest that these events were not continuous; the first event had about seven pulses within a 14-minute period, and the second had three pulses. Frequent small rockfalls have occurred in the same area during the rest of the day.

Apart from the large rockfalls, seismic activity in the last 24 hours has been generally quiet. Ten long-period earthquakes have been recorded, along with about 50 small earthquakes associated with continued dome growth. These "hybrid" earthquakes are recorded only at the closest seismic stations. In addition, two volcano-tectonic earthquakes were located, at a depth of 5 km beneath Centre Hills and at 2 km beneath Whites.

The eastern EDM triangle was measured today, and showed almost no change since yesterday. The daily measurements of the EDM lines to Castle Peak continue to show only very slow deformation of about 1 mm/day.

Measurements from Whites this morning showed that the tallest spine, which is currently the highest point on the dome, has increased in height by about 30 ft since yesterday. Dome growth in English's Crater continues, and further rockfalls and ash clouds are to be expected. The Tar River area continues to be dangerous, and the public are strongly advised not to proceed beyond the Tar River Estate house.

A new seismometer was installed at Long Ground this morning. This is a different type of instrument from the seismometers in the rest of the network, and will operate in conjunction with the existing Long Ground station. The new instrument records more information about seismic signals, and will be used to help scientists understand the processes occurring in the volcano.

Late note: A further rockfall event occurred at 17:25 this evening. It produced a large ash cloud that drifted west.

Montserrat Volcano Observatory