Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 10 July
to 4 pm 11 July 1997

The alert level system has been revised by zones

Visible activity at the volcano has continued at about the same level as yesterday. The seismicity is dominated by rockfalls. A few small pyroclastic flows have occurred in the Gages valley and Mosquito Ghaut.

The amplitude of the cycles defined by the Chances Peak tilt station has continued to decline and is now almost down to background level. Only one cycle was recorded during the period, peaking at about 8 am this morning. No hybrid earthquakes or tremor were associated with this cycle. Several small pyroclastic flows and ash eruptions have occurred throughout the cycle, but have been more prevalent on the deflation stage.

55 rockfall signals, 3 hybrid and 4 long period earthquakes were the only signals recorded by the seismic network today. There were no volcano-tectonic earthquakes recorded.

The EDM line between Waterworks and Lees Yard was surveyed again today. The data collected from these stations are still insufficient for any clear trends to be defined.

The cyclic pattern which has been defined at the volcano during the past few weeks appear to be changing. Pyroclastic flow and ash eruptions have occurred during the past two days with no preceding increase in seismicity or direct association with the tilt cycle. This means that people entering the designated exclusion zone put themselves at extreme risk. 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.

Plymouth is particularly vulnerable since pyroclastic flows have begun to enter the Gages valley without warning and have the potential to reach the coast. Persons entering these areas place themselves in extreme danger.

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.

Montserrat Volcano Observatory