Government Information Service

The Volcanic Explanation
For The 24 Hour Period Ending 6 PM On Saturday December 28, 1996
A Presentation Of The Government Information Services
In Conjunction With The MVO.

There have been numerous rockfalls from east and north-east sides of the October 1 dome. Many of these produced small ashclouds which resulted in light ashfall in St. Patrick's and Amersham during most of today (Saturday). The October 1 dome continues to grow and the new material on top of this dome is darker in colour and is probably hotter than the older material.

Seismicity is still high and there is some concern that with the changing nature of the activity there is a danger that it might escalate with little or no warning. This escalation could mean large pyroclastic flows into the Tar River Valley or the sudden collapse of the Galways Wall. The banded seismic tremor which has been prevalent since December 22 stopped yesterday afternoon. The last noticeable peak occurred at about 11 am yesterday. There have been 171 hybrid events and 75 rockfalls during this reporting period. This has been randomly spaced, but there were two small peaks at 9 am and 2 pm today. These may be the start of regular spaced seismic activity.

The EDM measurement of December 26 on Castle Peak shows a small amount of shortening of the line. The rate has again dropped today. The appearance of new material on the October 1 dome coincides with the drop in the deformation rate.

GPS measurements were taken today on the western side of the volcano. Theodolite measurements were also taken to detect recent grown of the dome. These measurements will be used with photographs of the dome from fixed positions for further analysis.

COSPEC measurements were made yesterday and today to measure the sulphur dioxide coming from the volcano. These are the first COSPEC measurements since the failure of the COSPEC in mid-November .Yesterday the average was 350 tonnes and today it peaked at 400 tonnes after one of the peaks in seismic tremor. These levels are similar to October and November.

The alert level remains at ORANGE which means there should be on one in Zones A,B,C, and D on the revised volcanic alert map for December. No one should try to sightsee the volcano from within these zones during the holiday period.

Dr. Sayadul Arafin returned to SRU today at the end of his tour of duty at the MVO

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