Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 10April
to 16:00 11 April 1997
The alert level was change to ORANGE this afternoon

Activity has been at an elevated level today. A period of continuous pyroclastic flow activity occurred between 9:42 am until 12:17 pm. This was not preceded by any change in activity and since lunch-time the seismicity has returned to the background level of the last few days.

Seismic activity overnight was low with only a few rock-fall signals recorded by the network. A moderate pyroclastic flow signal occurred at 4:50 am following a period of low amplitude tremor on all stations. However, activity increased gradually from 9:42 am with the recurrence of low amplitude tremor on all stations, and moderate to high amplitude tremor on the Gages seismometer. The tremor gradually increased until near-continuous pyroclastic flow activity occurred between 11:00 am and 12:17 pm. At times the level of the seismic signals exceeded the maximum recording amplitude on at least three of the short period seismometers. The intensity of the activity was greater than that of the elevated episodes of Easter weekend, but still did not reach the levels of September 17th, 1996. There were no obvious pre-cursory signals for this episode and, since lunch-time, the seismic activity has dropped down to background level.

In total only 5 volcano-tectonic and 5 long period earthquakes were recorded in the reporting period, together with 32 rockfall signals. This is not a significant change in numbers of earthquakes relative to the activity over the last few days.

Visibility of the volcano was poor during the height of the activity, but ash clouds could be seen to rise rapidly to levels of 7,000 to 13,000 feet (2000 to 4000 m) above sea level.

A helicopter flight this afternoon, following the period of heightened pyroclastic flow generation, allowed good views of the White River valley, but low cloud prevented detailed inspection of the dome. The rock fall debris in the chute through the Galway's Wall, that had accumulated since last week, has been eroded away again, but the depth of the chute is not deeper than after last week's activity.

The pyroclastic flows travelled further down the White River and the longest flow reached to 50 m upstream of the bridge across the White River at O'Garra's. The flows had also spread more widely across the valley, and there is more material deposited in the area around Galway's Soufriere and the road to the soufriere. Burning trees were observed at the end of the deposits.

A GPS survey was carried out on the western side of the volcano today. The data will be processed tomorrow. The rate of sulphur dioxide emission was measured this afternoon using the MiniCOSPEC. The data are currently being processed.

The alert level was raised to ORANGE this afternoon. The pyroclastic flows today show that the activity can escalate with very little precursory activity, and further collapses could occur. Daytime visits to zone C should be kept short, and nobody should enter zones A and B, which includes St Patrick's and Long Ground. People should not remain in zone D tonight. People should remain alert and continue to use ash masks when necessary.

Dr Simon Young arrived on Montserrat this morning to take up the Chief Scientist post.

Montserrat Volcano Observatory