Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 8 August
to 4 pm 9 August 1997

Over the last 24 hours there has been a sudden change to the cyclical patterns of explosive activity previously observed over the past 5 days. There was an explosive eruption last night 2051. The explosion which was expected to occur this morning between 0700 and 0900 did not take place.

Yesterday evenings explosion was preceded by a swarm of hybrid earthquakes which consisted of 31 discrete events between 1600 to 2042. The explosive eruption occurred at 2051. A loud rumble was heard at the MVO and a red glow appeared over the vent. Incandescent material then showered down to the North and over Gages. Several intense bursts were also noted. Heavy ash and fragmented pumice fall was experienced in Old Towne for about 20 minutes after the eruption. It is not yet known if there were associated pyroclastic flows.

Precursory hybrid activity began again at 0506 today. The frequency of the individual events gradually increased until by 0800 the discrete events had merged in continuous high amplitude tremor. The tremor had identical spectral characteristics to individual hybrid events. This level of activity continued for around 2 hours then decayed until the swarm ended at 1320. Very similar activity preceded the catastrophic pyroclastic flows of the 25th June 1997, fortunately in this instance no collapse or explosion occurred. A second hybrid swarm of slightly lower intensity began at 1421 and ended at 1657, comprising of 31 events. These events were similar in character to those in the previous swarm.

The earthquake count for the reporting period is 4 rockfall signals, 14 long period earthquakes and 158 hybrid earthquakes. However, the actual number of hybrid events is expected to be much larger as during continuous tremor periods events do not trigger the system.

All ghauts on the volcano are now filled with hot pyroclastic flow deposits and under no circumstances should people venture into this area. It is expected that as the current elevated level of activity continues further pyroclastic flows will occur on all flanks of the volcano. This makes Plymouth extremely dangerous. The Belham River valley is also very dangerous and should not be entered at all. Access to the exclusion zone is completely restricted, and people should stay away from the flanks of the volcano. The central zone is evacuated overnight and people should not return to there homes until advised to do so. After an explosive event moderate ash fall can be expected throughout the island. When this occurs people in the northern zone should stay indoors until the fall is over. Ash is present in the atmosphere and dust masks should be worn outdoors.

Such changes in the pattern of activity further emphasize the inherent unpredictability in the volcanic system. The risk of further explosions remains high. People should remain vigilant and continue to listen to radio Montserrat for any announcements.

Montserrat Volcano Observatory