The level of volcanic activity has increased slightly in the last 24 hours, with two swarms of volcano-tectonic earthquakes and further growth of the recent extrusion. Frequent moderate-sized rockfalls were observed this afternoon, producing some ash.
Visual observations were made today from both the ground and the helicopter. The recent extrusion has not grown much in height, but it has extended sideways to the east and north-west. The eastern face, above the remains of Castle Peak, looks very unstable, and several rockfalls were observed from there this afternoon. At times this afternoon the rockfalls were frequent, and ash production was nearly continuous. Some changes were noted to the large crack on the north-east part of the October 1 dome, and there is now a clearly defined crack that may allow a segment of the dome to collapse down into the northern Tar River valley.
No major changes were seen to the Galway's Wall, although a little more dome material has gone over the top of the wall since yesterday.
There were two swarms of shallow volcano-tectonic earthquakes during the period, from 5:20 pm to 8:10 pm and from 6:00 am to 7:48 am. A total of 72 earthquakes were recorded in these swarms. The level of recorded rockfalls continues to be low, with only 7 today, but the level of visual rockfall activity has certainly increased.
The results of yesterday's COSPEC runs are now available, and show an average sulphur dioxide flux of 780 tonnes per day. This is slightly higher than the recent background rate, although not as high as the maximum values commonly measured after dome collapses.
A survey of the western GPS network was carried out today. The results are not yet available.
The eastern face of the dome is steep, and likely to collapse soon. Any collapse is likely to be gradual, although a larger collapse cannot be ruled out. An explosion similar to that of September 1996 could result in the event of a major collapse which lasted for several hours. Zone E, which includes Cork Hill and the airport, remains safe. The Tar River Valley and the upper Galway's area are very dangerous.