Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 29 June
to 4 pm 30 June 1997
The current alert level is ORANGE

Volcanic activity has been elevated today with a continuation of the cyclic pattern of low activity followed by hybrid earthquakes and pyroclastic flows. Three episodes of pyroclastic flow activity occurred over the last 24 hours at 9 pm, 4:45 am and 12:30 pm.

The hybrid swarm that started yesterday afternoon at 2 pm continued until about 8 pm last night. The swarm consisted of many small events interspersed with larger hybrids. The end of the swarm coincided with a drop in the tiltmeter readings. Several small pyroclastic flows then occurred between 9 pm and 10:30 pm down Mosquito Ghaut and into Fort Ghaut.

This cycle was repeated at 2:15 am with a resumption of hybrid earthquake activity. This second swarm was less intense and of shorter duration than the previous swarm with fewer and smaller events being recorded, but this was followed by major pyroclastic flow activity from 4:45 am until 7:30 am. The eruption column from this episode reached approximately 15,000 feet, and drifted to the west over Plymouth. A helicopter from HMS Liverpool reported minor pyroclastic flows down Mosquito Ghaut after 6 am, but most of the activity appeared to be down the Gages valley towards Plymouth. Again the end of hybrid activity and start of pyroclastic flow activity was marked by a decrease in tiltmeter readings.

The third period of pyroclastic flow activity started at 12:36 pm with a small flow down Mosquito Ghaut. This again followed a hybrid earthquake swarm. Background tremor increased from 12:30 pm until 2 pm after which the pyroclastic flow activity increased markedly with major flows down both Mosquito Ghaut and Fort Ghaut. Observations from a helicopter flight shortly after the activity decreased showed that the flows in Mosquito Ghaut had reached Harris, and had not gone further than the flows of yesterday morning. However several houses were burning in the Windy Hill area. The flows down Gages Valley had gone further than any other flows in this area with the maximum run-out distance to within 500 m from the sea. There were reports of burning houses in Gages Village and near the Glendon Hospital in Plymouth. In addition there was also burning vegetation in Spring Ghaut in Upper Amersham. A large ash cloud was associated with this eruption and the pilot of an aircraft in the vicinity reported that the top of the cloud was at approximately 40,000 feet. This ash drifted slowly to the west and north.

In total, 77 rockfall signals, 110 hybrid and 27 volcano-tectonic earthquakes were recorded by the seismic network. However, the Gages seismometers were both knocked out by today's activity.

It seems likely that the cyclic nature of the activity will continue with repeated periods of pyroclastic flows giving rise to ash clouds away from the volcano, and thus people in the safe zones should stay alert and listen to Radio Montserrat. The pyroclastic flows may travel further than before. The current area of pyroclastic flow activity makes Mosquito Ghaut and Gages the most likely pathways, but further flows in Tuitt's or Tar River are probable as well. Much of Mosquito Ghaut and Fort Ghaut are filled with material which will enable the surge component of any flow to spread more easily over a larger area. Access to Plymouth is completely restricted. Zones A and B are extremely dangerous and nobody should go into these areas at all.

The Belham River valley is very dangerous. It may provide a pathway for further pyroclastic surges and there is also a risk of hot mudflows which may form rapidly if there is a period of heavy rain. Mudflows travel extremely fast and may be near boiling point, they may extend much further along the Belham River valley than the pyroclastic surges.

The pyroclastic flow and surge deposits will remain extremely hot for several days. Residents must not approach, attempt to handle or walk on the deposits because of the risk of severe burning. There is a risk of hot mudflows in some of the ghauts if heavy rain falls, and these would be extremely dangerous for anyone caught in their path.

There is likely to be some re-suspension of ash in the air today especially if it does not rain. Residents and workers are urged to wear a dust mask.

The airport is closed today and will remain closed until further notice.

Montserrat Volcano Observatory