Montserrat Volcano Observatory

Morning Update
Report for the period 16:00 16 September
to 07:00 17 September 1996

Volcanic activity overnight has continued at a relatively high level. Two volcano-tectonic earthquake swarms occurred during the reporting period. The first VT swarm occurred between 19:20 and 20:00 yesterday night (September 16) and the second between about 02:36 and 03:10 this morning (September 17). The first swarm was immediately followed by a period of near-continuous rockfall activity which continued up to 23:20 last night. A period of near-continuous rockfall activity also began after the second swarm but some VTs were also recorded during the early stages of the high rockfall activity. This second period of rockfall activity continued until about 05:57 earl this morning. The vT swarms were quite similar to those seen over the previous several weeks and preliminary indications are that these earthquakes are also located beneath the crater at shallow depth (above 2 km). Several large rockfalls or pyroclastic flows occurred during both periods of near-continuous rockfall activity. Tremor has been intermittent and broadband in nature throughout the night.

Visibility during the early morning was very poor due to low cloud cover at the volcano. However, the early morning period of high rockfall activity produced an ash cloud which was observed by Brambles airport at about 05:58 drifting towards a north to north westerly direction. The height was estimated to be 7000ft; this event was directly correlated with one of the largest rockfall signals which was recorded by seismic stations at 05:57.

Further rockfalls and pyroclastic flows will occur but all indications continue to be that the flows will be confined to the Tar River Valley area. However, areas affected by associated ashfalls will depend on the direction and strength of the wind at the time. Scientists are anticipating enhanced ash generation over the next few days if the dome undergoes partial collapse as expected. Dust masks should be worn at all times in ashy environments.

The Tar River Valley and surrounding areas are extremely hazardous and should not be entered under any circumstances.

Montserrat Volcano Observatory