Volcano Listserv Messages (2006)

• Subject: MVO Report for the period midday 22 December to midday 29 December 2006
• From: Kimberly.Genareau@xxxxxxx
• Date: Fri, 29 Dec 2006 13:34:04 -0700

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Montserrat Volcano Observatory
Report for the period midday 22 December to midday 29 December 2006 
From: Vicky Hards <vicky@xxxxxx>
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Dome growth during the period appears to have undergone a marked increase in 
rate, and the focus appears to have shifted entirely to the western side of the 
dome. A high whaleback lobe directed towards the southwest was observed on 26 
December, and the whole western side of the dome has also bulked up. The dome 
remains contained to the north and west. This switch was marked by the onset of 
ash venting at around 09:40 (local time) on Sunday 24 December from a vent on 
the western side of the dome, possibly behind Gage's wall. This venting was 
accompanied by low-level tremor becoming noticeable on the MVO seismic network 
by 11:00. Ash clouds reached a estimated maximum of 12,000 feet during the 
early afternoon. At 13:30 a pyroclastic flow came over the crater rim into the 
upper reaches over Tyre's Ghaut (northwest) travelling slowly for a 2-300 
meters. At around 17:20 another small pyroclastic flow was observed in the 
upper reaches of Tyres Ghaut and venting became more energetic, possibly 
hotter, with ash clouds rising more rapidly despite strong winds (23 knots). At 
this point the decision was taken to raise the alert level from 3 to 4. After 
dark incandescent rockfalls were clearly visible on a sector through from the 
northwest to west and clearly visible from the Salem/Old Towne area, suggesting 
a switch in the focus of dome growth. Clear views early on 26 December revealed 
that the western part of the dome, which has been inactive for some months, had 
bulked up significantly. At around 15:30 on 27 December a distinct pulse of 
venting was observed comprising red-brown (possible old) ash. At 11:15 on 28 
December a small pyroclastic flow was observed in Gages Valley, although the 
run out was very limited. Low level gas [and ash] venting from vent on western 
side of dome has been and is still ongoing, and overnight was accompanied by a 
loud roaring sound, reportedly audible as far north as Olveston.


The most notable seismic activity during the period was a tremor episode 
started at around 11:00 on 24 December culminating in a swarm of low frequency 
events (best described as long-period earthquakes), beginning at around 20:00. 
This swarm included 88 triggered events and was most intense between around 
22:30 and 23:30. The swarm finally died away at around 00:30 on 25 December and 
seismicity returned to previous background levels. There was another short 
burst of tremor on 27 December at 15:18 which continued for about 20 minutes. 
Subsequently activity has continued at relatively low level for the remainder 
of the period, dominated by rockfalls and long-period rockfalls. During the 
period the seismic network recorded 396 rockfall signals, 57 long-period 
rockfall signals, 163 long-period earthquakes, 6 volcano-tectonic earthquakes 
and 3 hybrid earthquakes.


The measured sulphur dioxide (SO2) flux rate during the period was low, ranging 
from a maximum of 551 tones per day (t/d) on 24 December to a minimum of 85 
t/d, with an average of 200 t/d. Nevertheless, it should be noted that the 
emissions plume from 24 December onwards has contained significant amounts of 
ash, therefore these values are probably only indicative of relative highs and 
lows within the period, not absolute values. 
 

The alert level stands at 4.  
 

Residents of Montserrat and visitors to the island are advised to tune into ZJB 
Radio for up-to-date information on the volcano. Access to all areas south of 
the Belham Valley [excepting Isles Bay Hill] is now suspended. The daytime 
entry zone, comprising the top part of St. George's Hill, is closed. Access to 
all areas south of Richmond Hill, and south of Jack Boy Hill to Bramble airport 
and beyond is prohibited at all times. The maritime exclusion zone around the 
southern part of the island extends 4 km off shore from Spanish Point to Roches 
Yard on the east side of the volcano, 2 km offshore from O'Garras to Gingoes on 
the south-west, and 200 m offshore from Plymouth.

For further explanations of the volcanic phenomena described, and information 
about the Soufrière Hills Volcano and the ongoing eruption, please look at the 
MVO website: http://www.mvo.ms <http://www.mvo.ms/> .

29 December 2006.

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Dr Vicky Hards
Director
Montserrat Volcano Observatory
P.O. BOX 318 
Flemmings
Montserrat
West Indies.

Tel: 1-664-491-5647 
FAX: 1-664-491-2423 
Email: vicky@xxxxxx  
http://www.mvo.ms <http://www.mvo.ms/>