Volcanic activity has continued at a slightly enhanced level during the last 24 hours. There have been few earthquakes, but several rockfalls and pyroclastic flows. Yesterday's survey of the dome gave a volume of 49 million cubic metres, with a rate of growth that has been almost constant all month.
A total of 5 volcano-tectonic, 2 hybrid and 6 long-period earthquakes were recorded. There were 15 rockfall signals. The largest signals, at 10:45 am and 3:30 pm today, were from small pyroclastic flows over the Galway's Wall.
Observations were made today from the helicopter in clear conditions. The southern area of the dome remains active, and several rockfalls were observed from the helicopter. The rest of the dome was inactive. A visit was made to the cracks on the eastern shoulder of the Galway's Mountain, where several new cracks have developed in the last few days. The crack that was measured on 25 March has not changed since then. There have been further changes to the Gages Wall area, and some more landslides have occurred since yesterday.
The EDM measurements made on the western triangle yesterday showed some changes in the line lengths between the Amersham points and Chances Steps. These lines have shown no consistent trends in the last few months.
The results of yesterday's full dome survey were processed last night. The survey was made from the helicopter using range-finding binoculars and GPS, and gave a total volume of 49 million cubic metres, the largest the dome has ever been. The rate of growth has been constant for most of this month, at about 1-2 cubic metres per second. The dome has grown in the summit region since the last survey on 19 March, with the most active area being on the south side of the dome. The top of the dome is now at 965 metres, or 3170 ft. This is almost as high as the previous maximum height, which was recorded in July 1996.
The COSPEC runs made on 24 March have been processed, and gave an average value of 200 tonnes per day of Sulphur Dioxide. Further measurements have been made today, but the results are not yet ready.
The dome is now very big and still growing, and a dome collapse with large pyroclastic flows could happen with little warning. It is dangerous to spend the night in evacuated areas, because the situation could worsen rapidly over a period of a few hours. People entering Zone C are reminded to remain alert at all times, and spend the minimum possible time in the evacuated zone. The Tar River Valley and the upper Galway's area are very dangerous and should not be entered at any time.