Montserrat Volcano Observatory

Weekly Report
Report for the period 5 p.m. 7 May 1999
to 5 p.m. 14 May 1999

The level of activity at the volcano has been higher this week when compared with the previous week.

A total of 120 rockfall signals, 1 long period, 1 hybrid and 55 volcano-tectonic earthquakes were recorded over the last week. The signals were evenly distributed throughout the week.

Four episodes of venting occurred during the period. The first of these was on 7 May. It began at 23.19 local time and lasted for about 8 minutes. It produced an ash cloud which rose to an altitude of about 10,000 feet and drifted north-eastwards, producing a light dusting of ash over the north of the island and also on Antigua. A small ash-venting event also occurred on the following day but only lasted for about a minute.

An explosion occurred on 10 May. This began at 10.23 local time and lasted for about 10 minutes. A plume of ash quickly rose to 30,000 feet and drifted to the north-north-east. Pyroclastic flows were seen travelling down the valleys of the Tar and Gages rivers and in Tyers Ghaut, although a subsequent observation flight only confirmed the presence of new deposits in the upper reaches of these drainages. Light ashfall was experienced throughout the north of the island for several hours after the event.

On 14 May at 4:07 pm, a small ash venting episode produced an ash cloud to less than 10,000 feet which drifted to the north-west.

Occasional observations during the week showed that fumarolic activity was still vigorous within the eroded dome at the top of the Tar River valley and also on the northern lobe of the dome. A reasonable view of the dome on 13 May was obtained, and it appeared that a large slab of rock had collapsed from the Galways lobe into the gulley between the top of Gages and Tar River valleys. This filled in the crater that had developed as a result of the explosions over the last few months.

Residents of Montserrat are advised to keep listening to ZJB Radio Montserrat for information in case of any changes in the state of the volcano.

Montserrat Volcano Observatory