Further pyroclastic flow activity occurred yesterday evening, resulting in a large ash cloud that was blown to the north-east, covering much of Montserrat in a thin coating of ash. Since late last night, the activity has been at a low level, although rapid dome growth has continued in the area of yesterday's collapse.
A total of 19 volcano-tectonic and 25 hybrid earthquakes were recorded. There were also 26 rockfalls and 4 long period events. All earthquakes occurred at shallow depths beneath the crater and were of magnitude less than 1.5.
Excellent views of the dome were possible from around the volcano and from the helicopter today. Last night's activity left a large scar in the overlapping structure formed by the October 1 and December 11 domes. The scar is located to the south-west of Castle Peak. A detailed survey of the dome was not possible because of ash being blown around the crater area.
The pyroclastic flows started at 6:24 pm, and peaked at about 7:05 pm. The flows were not as large as those of Thursday 16 January, but the total volume of lava lost from the dome in the event was larger. It is believed that last night's flows were hotter than the ones last week. As a result of this a large proportion of the collapsing material got converted into a large ash column. The flows travelled down the Tar River valley to the sea, and some trees on Perches Mountain were set alight. Reports of flashes of fire seen from the summit of the volcano were probably caused by glowing which was reflected in the ash and clouds above the volcano.
The ash cloud reached to about 30,000 ft above sea level. Two plumes of ash resulted- between 5,000 and 10,000 ft the ash was carried to the south-west. At higher levels, the ash was carried to the north-east, and there were reports of ash reaching Antigua. Some wet ash fell over the north and east of Montserrat.
COSPEC and GPS campaigns were carried out today. The results of the COSPEC measurements were not ready for publication. The GPS experiment was configured to test if the Dagenham to Whites line had lengthened since November 19 1996. The results suggested that it didn't.
The south-eastern and sector of the dome is still active and is therefore unstable. Further pyroclastic flows are likely in the next few days. Although the dome is likely to collapse in small chunks, producing small to large pyroclastic flows, a major collapse can not be ruled out. Should this occur, another explosion similar to that of September 1996 could result. It is however expected that there would be several hours of high level pyroclastic flow activity before any explosion. Zone E, which includes Cork Hill and the airport, remains safe.