Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 19 December
to 16:00 20 December 1996
The current alert level is RED

There were a series of moderately large pyroclastic flows down the Tar River valley yesterday evening, and concerns that these pyroclastic flows might trigger a vertical explosion meant that the alert level was increased to Red. The pyroclastic flow activity stopped after four hours, and the volcano was quiet overnight. However, a volcano-tectonic earthquake swarm started this afternoon. The alert level remains at Red, and nobody should be in zones A to E.

The pyroclastic flows were caused by collapses from the eastern side of the December 11 dome. The flows travelled onto the fan at the base of the Tar River valley, and to within 40 metres of the sea. The main activity built up rapidly from 5:06 pm to a peak just before 6 pm. The pyroclastic flows generated ash clouds which rose to around 10,000 ft above sea level, and were carried to the southwest by the light winds.

Observations from the airport during the major pyroclastic activity suggested that fresh lava was being supplied to the dome nearly as quickly as it was being lost in pyroclastic flows.

A helicopter inspection this morning of the crater area showed that last night's collapses came from the December 11 dome, and that some of the pre-September dome was also involved. All the pyroclastic flows were channelled to the south of Castle Peak, down the Hot River valley. There was also some minor renewed activity at the northern side of the October 1 dome.

The level of seismicity was moderate until 12 noon today. Twelve rockfall / pyroclastic flow signals and four long period earthquakes were recorded. Another volcano-tectonic earthquake swarm started at 12:21 pm today. This swarm has already reached the level of intensity of the previous two swarms, although the maximum size of the earthquakes is not yet as large as before.

Gravity measurements were made today on a line of stations on the eastern flank of the volcano.

A video produced by MVO showing Galway's Wall and the new dome will be shown on Local Access Television, Channel 5, at 1 pm tomorrow (Saturday)

Montserrat Volcano Observatory