Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 7 July
to 4 pm 8 July 1997

The alert level system has been revised by zones

Activity at the volcano has been at about the same level as yesterday with rockfalls and hybrid earthquake swarms being the main phenomena recorded by the seismic network.

The cyclic pattern established several weeks ago has continued with another hybrid earthquake swarm recorded during the period. This was ongoing at the start of the current reporting period and finished at 7.49 pm last night. The tiltmeters on Chance's Peak showed another peak at a little after 8:00 pm. No pyroclastic flow activity was observed to be associated with this tilt cycle but there were a few large rockfall signals as the tilt dropped. A further cycle peaked at about 11 am this morning and was followed by volcanic tremor and rockfall signals. No hybrid earthquakes preceded this episode, and no pyroclastic flows were observed. Some well developed ash and steam plumes were produced and rose to 10,000 feet as they drifted to the west.

51 rockfall signals, 56 hybrid and 3 long period earthquakes were recorded by the seismic network today which is about the same number as yesterday. Two of the rockfalls were preceded by long period earthquakes. No volcano-tectonic events were recorded. One near regional earthquake was recorded by the seismic network.

Further GPS measurements were conducted on the new deformation network at Garibaldi Hill, Lees Yard, MVO and the Waterworks. The line between Waterworks and Lees Yard was also successfully surveyed by the EDM. A permanent reflector has been installed at Lees Yard so that EDM measurements can be made from Waterworks. A 24 hour GPS experiment has been started at Lees Yard this afternoon to see if there is any movement of this site that can be correlated with the tilt cycle.

The volcano has been very cloudy today and no clear views have been obtained.

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 current area of activity in the crater makes Mosquito Ghaut and Gages valley the most likely pathways for pyroclastic flows, but further flows in Tuitt's, Tar River or White River are possible as well. Access to Plymouth is completely restricted.

The Belham River valley is also an area for anxiety over safety. 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. Residents and workers are also reminded to wear a dust mask when there is ash in the air.

Dr. Willy Aspinall (British Geological Survey), Professor Steve Sparks (Bristol University), Dr. Anne-Marie Lejeune (Bristol University), and Mr. Matthew Watson (Cambridge University) left Montserrat today after tours of duty at MVO.

Montserrat Volcano Observatory