Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 on 03 Feb. 1996
to 16:00 on 04 Feb. 1996

The very small hybrid (dominant frequencies of 3 to 5 Hz) earthquakes have decreased in size during the last day They are still occurring every 10 to 20 seconds but are so small that they are only recorded at seismic station MGAT (near Gages) and the new station MHR (at Hermitage), the two stations closest to the crater. The largest of these events probably did not exceed magnitude 1.0 but the vast majority were near magnitude 0.5. Long-period earthquakes (dominant frequency of 2 Hz) became more frequent near the end of the period; about 25 were recorded in all; 14 could be located and had depths from 1.4 to 1.7 km beneath the crater. Magnitudes of these events ranged from about 1.5 to 2.2. No volcano-tectonic (rock-breaking)earthquakes were recorded during this period. Broadband (dominant frequencies of 2 to 8 Hz) tremor increased in amplitude at the beginning of this recording period but decreased and disappeared by 0800. Four signals, of the type that have often been visually correlated with rockfalls, were recorded during this period; owing to poor weather, visual confirmation could not be made.

EDM measurements were completed on the Tar River-Castle Peak line today. This line experienced a shortening of 1.5cm since it was last occupied two weeks ago (21 January). This change represents a slight increase in the very slow long term trend of shortening observed on this line. This change correlates well with the apparent increase in rate of dome growth that has occurred during the past two weeks. An attempt was made to occupy the White's-Castle Peak-Long Ground; this was aborted due to the very low cloud cover.

Brief views of the northern and southern parts of the dome were obtained from the helicopter late on the morning of 4 February. Some growth has occurred on both parts of these actively growing areas, but the rate seems lower than during the past week. The talus deposits which now occupy most of the moat areas is now in contact with some parts of the crater walls and continue to build up. Steam emissions was observed from the topmost parts of the dome.

During the helicopter flight today, scientists observed several persons at the top of the old Castle Peak dome. The public should note that English's Crater is an area of extreme danger; large rockfalls and explosions occur in this area continuously and the new dome material is extremely hot (several hundred degrees Celsius) - these areas should be avoided at all times.

Montserrat Volcano Observatory