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MVO report: Partial dome collapse at Soufrière Hills Volcano
From: "Paul Cole" <paul@xxxxxx>
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Montserrat Volcano Observatory
Weekly Report for the period 5 to 12 February 2010
Activity at the Soufrière Hills Volcano has increased significantly this week with two vulcanian explosions and a partial dome collapse.
The two explosions occurred at 1:49 pm on Friday 5 February and 7:57 pm on Monday 8 February, lasted 7 and 6 minutes and ash plumes reached 25,000 and 15,000 ft respectively. There was no ashfall from either explosion in inhabited regions of Montserrat. Pyroclastic flows associated with the explosion on 5 February reached the sea at Aymers Ghaut and smaller pyroclastic flows (maximum run out 2 km) also occurred in several other valleys including Tyers ghaut. The 8 February explosion generated pyroclastic flows only in the Gages valley and these did not reach the sea.
During the first part of the week activity was concentrated on the western side of the dome. Beginning on 9 February the focus of activity shifted from the west more to the northern side of the lava dome, although pyroclastic flows on the morning of 11 February travelled to the west, northeast and north simultaneously.
The dome collapse event on 11 February lasted 55 minutes starting at 12:35 pm and reaching a peak at 13:04, although there were several pulses. Pyroclastic flows moved mainly to the northeast travelling across the sea at several points on the eastern side of the island. Pyroclastic surges moving over the sea on the eastern side of the island were visible from Lookout village. Significant deposition from pyroclastic flows has extended the coastline several hundred meters at the old Bramble airport. Pyroclastic flows also travelled northwest into Tyers Ghaut and down the Belham valley as far a Cork Hill. The ash plume reached 50,000 ft (from pilot reports) and drifted east and then southeast. Ashfall occurred in northeastern Montserrat, and was reported in southwest Antigua, Guadeloupe and Dominica. A large collapse scar has been excavated into the northeastern flank of the dome, although the summit of the original southwestern portion is still intact.
There have been five hundred and twelve rock fall signals, one hundred and forty one long period events, eighty two hybrid earthquakes and four volcano tectonic events recorded this week.
The Hazard Level is 4. There is no access to Zone C and only daytime access (6:30 am to 5:30 pm) to part of Zone B.
Additional information on the Soufrière Hills Volcano, the Hazard Level System and a glossary of volcanic terms can be found at can be found at the MVO website http://www.montserratvolcanoobservatory.info/index.php?option=com_content&view=article&id=254&Itemid=187&lang=en
Paul Cole
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