The volcano is still a threat to all the evacuated areas. Activity since yesterday has mainly been rockfalls from the October 1 dome as it continues to grow. Activity could escalate at any time with little warning. Pyroclastic flows into the Tar River Valley are the main hazard, but there are also hazards from a sudden collapse of the Galway's Wall which is still unstable. Either of these could have serious consequences for much of the evacuated area. There is therefore no access to zone A/B. Restricted access is allowed to zone C/D, but only for essential purposes and by people who can leave rapidly. There is normal occupation of all other zones.
Visibility has been good during much of this reporting period. Last night, rockfall activity from the October 1 dome continued at a level similar to that over the last few days. Rockfalls were occurring from all the visible parts of the dome and were almost continuous at times. It was possible to see that a considerable amount of material was falling down the northern flank of the pre-September dome towards the Farrell's Wall. Rockfall activity continued today, although at a slightly lower level. The new material being added at the top of the dome seems to have changed texture, and is more slabby than a few days ago. The rockfall activity produced some small ash clouds which were blown towards the west. These are noticeably smaller than from similar rockfall activity in the past.
Seismic activity is still dominated by banded tremor, hybrid earthquakes and rockfalls. The regularly-spaced banded tremor reappeared yesterday and continued throughout today, although the size of the signals has decreased slightly. The bands of tremor are approximately 5 hours apart. Hybrid and rockfall activity has also declined slightly since yesterday, with 24 hybrid events and 19 rockfalls being recorded by the seismic system. Two long-period earthquakes and two small VT earthquakes were also recorded.
MVO field teams made good use of the favourable conditions today to carry out a number of tasks.
The cracks on Chance's Peak were measured. The crack nearest Galway's Wall, which has shown the largest movements in the past, opened up by about 2 cm since it was last measured ten days ago. This represents a significant slowing down of the deformation rate of that crack, and perhaps of the wall. The field team also took the opportunity to clean the EDM reflector and make adjustments to the extensometer on Chances Peak.
Gravity and GPS measurements were made on the line from Amersham to Chance's Peak, up Chance's Steps. The EDM lines to Castle Peak and the one from O'Garras to Chance's Peak were shot successfully. Theodolite measurements were made of points on the dome to estimate the recent growth rate. This will be helped by photographs which were taken from fixed positions.
COSPEC measurements were taken of the level of sulphur dioxide in the plume.
Samples were obtained of rocks that have fallen from the December 11 dome and from the recent material at the top of the October 1 dome.
The sirens will be tested tomorrow, between 3 pm and 6 pm.
MVO would like to thank everyone on Montserrat for their support and co-operation during 1996. We look forward to continuing good relations in 1997.