The level of activity at the volcano has continued to be quite low. Two swarms of earthquakes were experienced today. Visibility has been quite good for the entire day and rockfall activity was noted on the southeastern side of the dome.
Seismic activity has been dominated by the occurrence of two swarms of earthquakes consisting of volcano-tectonic and hybrid events. The first swarm occurred between 21:01 on 18 February and 02:44 on 19 February and included 46 VTs and 7 hybrids. The second swarm started at 10:43 today and continued to the end of the reporting period. A total of 63 VTs and 34 hybrids were recorded during the entire reporting period. Thirteen rockfall signals were also recorded during the period; some of these developed into small pyroclastic flows with associated ash clouds which drifted towards the west.
Visibility was very good for most of the day and excellent views were obtained from several vantage points around the volcano. Most of the rockfall activity is still concentrated in the active south-east part of the dome. A few small pyroclastic flows were also observed to originate from the area of the Castle Peak chute. A few small rockfalls were seen from an area between the October 1st dome and the northern part of the September 17th scar. Some steaming was also noted from the northern parts of the dome. Very little activity was observed on the Galway's wall and the areas appears to have undergone little change since yesterday.
EDM measurements were made on the radial lines between lower and upper Amersham and between lower Amersham and Chances Peak steps; the results of these measurements are not yet available. A GPS survey of the BIGNET which involves stations that skirt the flanks of the volcano was conducted today. The survey had not been completed by the end of the reporting period and the results will be reported in a later report.
The results of the dome survey conducted on 17 February has now been finalised. Data collected indicate that the mean extrusion rate of material at the dome has been 2.7 cubic metres per second since 11 January. The total volume of the dome has been calculated as 40.23 million cubic metres (35.78 million cubic metres dense rock equivalent). This compares with 35.56 million cubic metres (31.63 million cubic metres dense rock equivalent) on 11th January.
The dome is currently larger than ever before, and so further dome collapses and pyroclastic flows are expected. These will probably follow the recent pattern, but a change in the activity could occur at any time. Visitors to zone C are reminded to remain alert and responsible at all times, carry ash masks and spend the minimum possible time in the evacuated zone. It is advisable to have access to a battery operated radio in case of electricity power cuts. Ash levels in Plymouth are hazardous, especially during dry, windy weather, and so it is essential to wear masks in areas affected by ash. Flash floods could cut off access to areas south of Fort Ghaut; visitors should leave that area when it rains. The Tar River Valley and the upper Galway's area are very dangerous and should not be entered at any time.