Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 29 May
to 16:00 30 May 1996

Volcanic activity at the Soufriere Hills volcano is still dominated by rock avalanches from the growing lava dome which produced small ash clouds. Activity today has been less than yesterday.

Seismicity has been dominated by small- to moderate-sized rockfall signals. The number of these has decreased noticeably, with 33 rockfall events recorded today compared to 103 yesterday. The largest signals occurred at 22:35 on 29 May and at 13:34 and 15:00 on 30 May. These, and other rockfalls, produced small ash clouds which drifted on very light winds to the west. The largest ash cloud was associated with the 15:00 rockfall, but was only a few hundred feet.

Five long-period earthquakes and no hybrid events were recorded by the seismic network. One VT earthquake was recorded, at 15:03 on 30 May, immediately after the largest rockfall. The VT earthquake was located at a depth of 0.75 km beneath English's Crater. It was followed within less than a minute by another, smaller, rockfall. It is not possible to say whether there is any link between the VT earthquake and the rockfalls. Intermittent low-amplitude broadband tremor has been recorded throughout the reporting period, with two distinct periods of near-continuous tremor; from 20:55 to 23:09 on 29 May and from 07:50 to 11:05 on 30 May.

>From late morning onwards, viewing conditions were excellent and a number of observations were made from the ground and from the helicopter. The dome continues to grow. There was vigorous steaming from many parts of the dome. Rockfall activity appeared to be concentrated on the northern and northeastern flanks of the dome. A new slab-like spine which had appeared high on the northwest flank of the dome appears to have broken off during the 15:00 rockfall. This descended the north western flank of the dome and generated slight ashfall in the Upper Gages and Amersham areas.

EDM measurements were made today on the eastern triangle. Line lengths to Castle Peak have shortened by 8 mm since these were last measured on 27 May. These results continue to indicate very small changes, consistent with slow deformation of the volcanic edifice It was not possible to make measurements with the new GPS equipment due to continuing technical problems.

Both COSPEC and FTIR measurements of gas concentrations in the volcanic plume were made today. The results of these are not yet available.

Mr Desmond Supersad of the SRU returned to Trinidad today after a 3 week tour of duty - he is replaced by Mr Lutchman Pollard, who arrived on island last night.

The present level of activity at the Soufriere Hills Volcano continues to cause concern to the scientists. The MVO urges that visits to the evacuated zone are kept to a minimum. The Tar River, Long Ground and Whites areas are extremely dangerous and should not be entered under any circumstances.

Montserrat Volcano Observatory