Montserrat 411 News

Heavy rain this week has generated lahars (mudflows) on several flanks of the volcano. On afternoon of 13 April large lahars occurred in the Belham valley. Many of these lahars were hot with abundant steam and geyersing associated with them. Two large fans were formed at the coast of Old Road Bay as a result of these events. These were the largest lahar events to have occurred since November 2009.

Several small areas of incandescence (glowing) visible to the naked eye have been seen on the lava dome on a number of nights this week. These are probably due to hotter areas of the dome being exposed by small rockfalls.

The average sulphur dioxide flux this week was 194 tons per day, with a daily minimum of 105 and a maximum of 304 tons per day.
The Hazard Level is 3. There is no access to the terrestrial Zone C and daytime transit access to shipping through the maritime extension of the zone.

Authorities say that although the decision to allow reoccupancy, residents need to be vigilant at all times because activity could escalate with very little or no notice. They added that residents maintain their properties in a state of readiness for possible evacuations.

Activity at the Soufrière Hills Volcano has been at a high level this week with periods of vigorous ash-venting taking place between the night of October 4 until midnight on October 7. Activity was then low until the early hours of October 9 when rockfall activity increased.

Seismic activity this week has been very high, with one thousand two hundred and twenty four rockfall signals, three hundred and eighty two long period events and one volcano tectonic earthquake.

Despite the slightly lower seismicity numerous pyroclastic flows have occurred in most of the major valleys that drain the volcano. The majority of rockfall activity is still concentrated on the southern side of the volcano, however vigorous pyroclastic flows have occurred sporadically in the Gages valley to the west, Tuitt’s Ghaut to the northeast, and there have been some moderate flows in the Tar River to the east. However no pyroclastic flows or rockfalls were observed in Tyers Ghaut.

There have been five hundred and seventy two rockfall signals, two hundred and thirty six long period events and five volcano tectonic earthquake recorded. Hybrid earthquakes have been recorded , since the afternoon of 30 October, for the first time since the renewal of activity with one hundred and eighty nine events triggering the system. Hybrid earthquakes are occurring in cycles of between seven and three hours long, with frequency of events increasing until they merge to tremor.

There have been four hundred and twenty nine rockfall signals, one hundred and thirty nine long period events, five volcano tectonic and forty one hybrid earthquakes recorded. The cycles of hybrid earthquakes merging to tremor ceased on Saturday 7 November. Although the frequency of rockfalls has decreased the size of the largest pyroclastic flows has increased.

There have been six hundred and forty-one rockfall signals, three hundred and thirteen long period events, two volcano tectonic and five hundred and fifty seven hybrid earthquakes recorded. Hybrid and long period earthquakes increasing in frequency to form banded tremor have occurred in regular cycles all this week.