Montserrat Volcano Observatory

Daily Report
Report for the period 16.00 23 May
to 16:00 24 May 1997
The current alert level is ORANGE

The level of volcanic activity has remained high, with further swarms of hybrid earthquakes and an increase in pyroclastic flow activity. Measurements made yesterday indicate an increase in the rate of deformation of the area around Chances Peak.

There have been two hybrid earthquake swarms during the period, with a total of 93 hybrid earthquakes recorded. Six long-period earthquakes also occurred. The first swarm started at 9 pm last night and continued until 4:11 am, and the second swarm began at 12:18 pm and was ongoing at the end of the reporting period. The number of earthquakes in the swarms is slightly lower than in previous days. The swarms occur fairly regularly, with between 16 and 20 hours between the start of each swarm. As before, the swarm in the early hours was followed by a period of enhanced pyroclastic flow activity. However the level of pyroclastic flow activity has been higher throughout today, with small flows on the northern side of the dome at regular intervals, and a total of 121 rockfall signals recorded. This continuous activity has resulted in light ash fall to the west of the volcano.

The results of a GPS survey on Chances Peak yesterday show that the peak has moved about 4 cm since it was last measured on 28 April. Also, the large crack across Chances Peak on the Galway's side was remeasured, and showed 6 cm of opening over the same period. The rate of shear movement along the crack has also increased slightly. These measurements show that there has been an increase in the rate of movement of Chances Peak in the last 3 weeks. The tiltmeters which have been installed in the huts at Chances Peak in the last week are also showing evidence of continued movement of the peak, with the volcano swelling slightly during each hybrid earthquake swarm.

No visual observations were made today, because of persistent low cloud. A further visit was made by helicopter to Chances Peak to finish the installation of the crack extensometer, and to retrieve data from the two accelerometers.

The northern EDM triangle was measured this afternoon, and the results will be reported tomorrow. The measurement of gas output using the COSPEC instrument is still being hampered by the wind direction, with the plume going to the west so that the normal route down the south-west coast cannot be used. An attempt was made to measure the sulphur dioxide flux with a traverse through the central corridor, and the results will be reported tomorrow.

The volcanic activity remains in a potentially dangerous phase, with the possibility of pyroclastic flows breaking into the northern ghauts. Dome growth continues and an escalation in the level of activity remains possible. The Tar River valley, Long Ground, White's and Tuitt's areas are very dangerous, and should not be entered because of the dangers of pyroclastic flows. Nobody should enter zones A and B, and only essential visits should be made to the evacuated zone. Ash masks should be worn when in the ashy areas.

Montserrat Volcano Observatory