Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 30 March
to 16:00 31 March 1997
The current alert level is ORANGE

Volcanic activity remained at a high level today. Further pyroclastic flows over the Galway's Wall occurred overnight, excavating a scoop into the dome on the south-western side above the Galway's Wall. A moderate sized pyroclastic flow also occurred from the eastern face of the dome into the Tar River.

A total of 2 volcano-tectonic, 12 hybrid and 8 long-period earthquakes were recorded. This is about the same number of these type of events as yesterday. However the seismic records have again been dominated by rockfall and pyroclastic flow signals. There have been 63 rockfall signals. Continuous rockfalls and pyroclastic flows over Galway's Wall occurred between 3:00 am and 5:25 am this morning. For a short period the signals exceeded the maximum level of tremor than can be recorded on the seismometers. Large ash clouds to over 10,000 feet were produced by this activity, and these drifted to the west over St. Patrick's and Plymouth. Three main pulses were recorded at 3:35 am, 4:18 am and 5:00 am. Activity decreased after this period with only small rockfalls and pyroclastic flows been detected. At 3:30pm the drum recorders were almost all saturated by a signal from a pyroclastic flow originating from the east side of the dome. Currently seismic activity is low.

Observations were made today from the helicopter throughout the day. The pyroclastic flows from the Galway's Wall were again confined to the bottom of the White River Valley with little damage to the sides of the valley. However a zone of surge damage was noted in the upper reaches of the White River today. Views of the south-western part of the dome revealed that a scoop-shaped scar has formed in the pre-September 17, 1996 and January 20 parts of the dome complex. The upper part of the scar is vertical and made up of spine-like structures. This area looks very unstable. A substantial amount of rockfall talus has also been built up at the base of the wall and the Galway's Soufriere has been almost completely buried by flow deposits. The Great Alp Falls have been extensively reduced in height due to burial by pyroclastic flow deposits. Some vegetation was observed to be burning along the length of the White River valley. The maximum run-out distance of the pyroclastic flows is now estimated to be approximately 3.65 km. Some erosion of the Galway's Wall by the flows has occurred but the main part of the wall remains intact.

Two pyroclastic flows from the eastern face of the dome were observed by a team at Whites this afternoon. The first of two reached just past the break in slope in the upper part of the Tar River Valley but the second reached within 50 metres of the delta. Vigorous convection of ash and well developed surge components were associated with both flows. This is the first activity of this type since February 12, 1997 (Ash Wednesday).

Measurement of ash thickness around the southern part of the revealed that over 1 centimetre of ash was deposited during yesterday and overnight in many places. Fifteen (15) millimetres of ash was recorded in Plymouth. This will make driving conditions hazardous and will be unpleasant for anyone entering this zone. It is very important at the moment that ash masks are worn during the present activity.

Today's heightened activity is a result of dome growth of the southern part of the dome adjacent to the Galway's Wall and shows that pyroclastic flows from the dome can occur at any time. The alert level has been raised to ORANGE as a temporary measure to allow MVO to thoroughly assess the situation. It is dangerous to spend the night in evacuated areas, because the situation could worsen rapidly again over a period of a few hours. People should not enter zones A, B, C and D tonight and should listen for further updates of the situation from the MVO. For the time being people are advised to remain vigilant while the new activity is being assessed and to always wear an ash mask in the dusty conditions. The Tar River Valley and White River area all the way to the sea are very dangerous and should not be entered at any time.

Montserrat Volcano Observatory