Montserrat Volcano Observatory

Daily Report
Report for the period 6 pm 20 October
to 6 pm 21 October 1997

There has been one explosion in the last 24 hours. This explosion was preceded by an earthquake swarm which began at about midday yesterday and was comprised of both VT and Hybrid events.

The explosion occurred at 7:02pm last night and an observation flight at about 10:30 am today showed that pyroclastic flows travelled down the Tar River valley, Whites Ghaut and Tuitts Ghaut. There was no evidence of fresh flows in the Gages valley, or in the ghauts between gages Valley and Galways or in Tyres Ghaut. The flows that travelled down the Tar River Ghaut went as far as the middle of the delta and fresh pyroclastic flow material was seen in the Whites River from the Galways area, to within a few hundred meters of the sea filling the sides of the valley. A deeply cut chute was also observed on the eastern side of the dome, that is the area over the Tar River Valley. That area is deeply undercut and slightly overhanging, indicating that more large pyroclastic flows can be generated in that area. After the explosion last night, there was pumice and light ash fallout from the plume in the areas from Salem to St.Peters. The sizes of the larger fragments collected by MVO field teams ranged from about 1.5cm in Salem, Old Towne and St.Peters to about 2.5 cm in the Woodlands area. The explosion column rose very quickly to between 15,00 and 20,000 feet drifted slowly Northwest, depositing a lot of the material in the sea. There was no report of ash fall further North of St.Peters from that event.

Seismicity has been at slightly elevated level from about 8:08 pm last night with the start of a volcano-tectonic earthquake swarm which was still going on up to the end of the reporting period. Some of these earthquakes are slightly larger than those seen over the last few days. There was reports of an earthquake which was felt in the Woodlands area by two scientists. This co-related with a large volcano-tectonic earthquake signal recorded on the network.

Between 4 o'clock yesterday afternoon and 4 o'clock today there were 95 hybrids, 69VTs, 16 long period earthquakes and 17 rockfall signals scattered throughout the reporting period. The explosion was followed by a period of tremor and ash venting.

The ash sampling program continued today and results indicate that the levels in the Olveston and Mango Hill area were low, but residents are still reminded that there is very light ash in many areas which will be re-worked during cleaning and other activities, and they should wear dust masks when operating in these areas.

More explosions are expected and larger explosions could occur without any warning change in seismicity. Recent explosions have sent pyroclastic flows into Plymouth, into the upper part of the Belham Valley and to the sea in the Tar and White rivers, and future flows will travel further still. Mu dflows are likely to continue in the ghauts as long as the rain continues. These mudflows could be hot and it is extremely dangerous to be in any ghauts in the southern part of Montserrat at the moment.

All residents of Montserrat are reminded to be vigilant, to avoid entering the evacuated zone and to stay tuned to Radio Montserrat for further information.

Montserrat Volcano Observatory