Smithsonian Institution
Global Volcanism Network Bulletin v. 20, no. 10, October 1995
Soufriere Hills (Montserrat)  Small ash explosions continue;
       three new vents formed; September dome grows

Soufriere Hills
Montserrat, West Indies
16.72N, 62.18W; summit elev. 915 m
All times are local (= GMT - 4 hours)

The observatory was moved on 1 October from the Vue Pointe
Hotel to Eifel House on Bishop View Road in Old Towne. A
phreatic eruption that day deposited ash across a large
area, including the capital city of Plymouth. This eruption
was followed by a volcano-tectonic (VT) earthquake swarm,
with 70 events located beneath the volcano at depths of 1-6
km. Two of the earthquakes, at 2257 and 2319, had magnitudes
of ~2.5 and were felt at the observatory; several were felt
in the Long Ground area. After about 0500 on 2 October, the
number of located earthquakes dropped to ~5/day. Two
episodes of low-amplitude broadband tremor recorded during
1-3 October were related to steam emission. Electronic
tiltmeter and EDM observations during that time revealed no
significant deformation.

EDM measurements at Tar River completed on 3-4 October
continued to show a shortening trend, signaling minor
inflation. Shallow VT (12 located events) and long-period (2
events) seismicity continued. Moderate levels of seismicity
prevailed during 4-8 October, with 30-40 shallow (< 6 km
depth) VT earthquakes each day, rare felt events (M 2-2.5),
and a few long-period events. No deformation was detected by
electronic tiltmeter.

An explosion around 2355 on 5 October caused heavy ashfall
in Plymouth and in the SW part of the island. On 5 October
the government announced that over the next two days they
would evacuate Plymouth~s home for elderly people and the
hospital, sending residents to the N part of the island.

Two eruption signals were recorded at 0235 and 0347 on 8
October, and the EDM line at Tar River continued to show
minor inflation. Seismicity began decreasing on 8-9 October,
when 24 earthquakes were located beneath the volcano, with a
few in the Centre Hills area. A small eruption at 1356 on 9
October generated light ashfall in Amersham and Upper Gages.
Vent 2 was emitting a small amount of steam again during 7-9
October. Several episodes of broadband tremor may have been
caused by increased steam emission. There were only 6
located earthquakes during 9-10 October, but several
episodes of broadband tremor. Another minor eruption around
0012 on 10 October caused light ashfall in Plymouth. Visual
helicopter inspection of the crater revealed significant
steam emission and an increase in the size of the 25
September dome (Bulletin v. 20, no. 9).

Formation of Vent 5 on 11 October. An ash eruption at 0021
on 11 October came from a new vent on the Tar River side of
the Castle Peak dome, and damaged the EDM reflector at Tar
River. A small earthquake swarm accompanied this vent
formation. There were two more small ash eruptions later
that day at 1540 and 1700. Although no significant changes
to the dome were noted, steaming continued from its top;
Vent 1 was also steaming, and appeared to be larger and
deeper. Scientists noted that steam emissions from the
crater had generally increased.

Three more ash eruptions occurred on 12 October, at 0901,
0955, and 1114. Continuous steam emission came from  several
areas in the crater and Vent 5. Two episodes of broadband
tremor during 12-13 October were attributed to increased
steam emission. Seismicity was low, with only 22 events
during 11-13 October. No deformation was detected following
this latest series of explosions.

Formation of Vent 6 on 14 October. An eruption at 0708 on 14
October created another vent on the NE flank of Castle Peak
dome, generated a significant amount of ash, and ejected
blocks as far as the edge of Long Ground, ~1 km E of the
vent. A pilot reported that the plume may have reached ~2 km
altitude. Another eruption at 1058 caused no reported
ashfall. Two gas venting episodes at 2200 and 2345 on the
14th were associated with a small earthquake swarm and
broadband tremor episodes. Vent 2 again emitted moderate
amounts of steam, accompanied by a loud roaring sound, and
Vent 5 continued to emit small amounts of steam. Seismicity
decreased from 18 events on 13-14 October to 5 events
accompanied by broadband tremor on 15-16 October.

Seismicity increased again on 16-17 October with 22 events
clustered in two areas: one beneath the volcano and the
other just E of Windy Hill. Steam-and-ash eruptions were
recorded by the seismic network at 1757 and 2245 on 16
October, and at 1150 and 1522 on the 17th. There were also
several episodes of broadband tremor and ~30 minutes of low-
frequency harmonic tremor starting around 0414 on 17
October. Later that morning an aerial inspection of the
crater showed no significant changes and little steaming.
During a second flight at 1145, a large mudflow originating
within the crater moat beyond Vent 2 was seen running
rapidly down the Hot River and reaching the sea. This was
probably the largest mudflow (in terms of volume of
material) since the current activity began.

During 17-18 October there were 12 scattered earthquakes,
several periods of broadband tremor, and some intermediate-
frequency tremor. Ash eruptions were recorded at 1739 on the
17th and at 0530 on the 18th. The dome area continued to
emit steam, but did not increase in size.

Formation of Vent 7 on 18 October. The 31 earthquakes during
18-19 October were clustered beneath the volcano. Several
broadband tremor episodes and one period of low-frequency
tremor were also detected. An eruption at 1621 on the 18th
was associated with the formation of a new vent within the
moat area of English~s Crater, just SW of Vent 1. Another
eruption was recorded at 2207 on the 18th. An explosive
event around 1516 on 19 October generated a mudflow down the
Hot River. During 19-20 October there were 28 earthquakes
located; the events were scattered throughout S Montserrat,
with some clustered beneath Soufriere Hills and St. Georges

There were 15 VT earthquakes on 20-21 October concentrated
around the Long Ground/Soufriere Hills area. Several
eruption episodes on 21 October resulted in ashfall that
affected villages in the E. Ash fell at the airport for the
first time, closing it briefly. No deformation was detected
at the Tar River EDM or Long Ground tilt stations.
Helicopter observations revealed that Vent 1 had extended E
and was responsible for the previous ashfall. There was a
small mud flow down the Tar River.

An average of 35 earthquakes/day occurred during 21-23
October. They were scattered throughout S Montserrat with
some concentrations in the Long Ground-Tar River area and
beneath the volcano. Some broadband tremor was also
recorded. Visual observation of English~s Crater both from
helicopter and Tar River on 22 October revealed light steam
emission from vents 2 and 5. When observed on the morning of
23 October, the September dome continued to steam, and was
covered with sulfur deposits; it may also have grown since
last observed on 20 October. Only one other small area SE of
the dome was steaming. An eruption at 1337 on 23 October
produced ash deposits within the summit crater and at Tar
River. Steam emission increased after this eruption.

Seismicity decreased following this eruption to 10-14
events/day through 29 October, except for 22 events on the
27th. Locations were mainly beneath the volcano, although
some were centered in the Windy Hill area and other parts of
S Montserrat. An eruption at 1325 on 25 October caused
ashfall in the Tar River area. Eruption signals were again
recorded at 2314, 2321, and 2347 on 25 October, and at 0447
on the 26th; no ashfall was reported. Several episodes of
low-amplitude broadband tremor were recorded during 25-26
October. EDM measurements at Tar River on 26 October
indicated a continuation of the minor inflation observed
during the past several weeks.

A steam-and-ash eruption at 1317 on 27 October from Vent 1
was followed by more than 30 minutes of low-frequency
tremor. Eruption signals were recorded at 0855 and 2018 on
28 October, but no ashfall was reported. Steam emission from
Vent 2 was observed that afternoon. Eruptions occurred again
at 0326 and 0857 on the 29th, both followed by broadband
tremor. An ash-and-steam plume was seen from the observatory
following the 0857 event. Steam was seen coming from Vent 1
during a helicopter flight, but no major changes were noted.

Seismicity increased on 29-30 October to 55 events; most
were clustered in a region just W of Windy Hill, with some
scattered in the Centre Hills and Soufriere Hills areas.
Eruption signals were recorded at 2110 on the 29th, and at
0244 and 1310 on the 30th. Two small long-period events were
recorded after the first eruption. Ash from the first two of
these eruptions was observed in English's Crater by
helicopter. The third eruption, witnessed by scientists at
the Tar River EDM site, produced a high column that caused
ashfall over a wide area. This ashfall was the most
significant since 21 August, and was accompanied by a
density current of ash in the Gages valley. The morning of
31 October visual observations revealed a significant
increase in Vent 1~s size, but the 25 September dome
appeared unchanged.

Seismicity decreased again the next day to 23 events, but
they were located in clusters in the Tar River-Long  Ground
area and W of Windy Hill. There were also 4 long-period
events and several episodes of broadband tremor. One
eruption at 1118 on 31 October had no reported associated
ashfall. EDM measurements at Tar River again showed a slight
shortening, associated with continued slow inflation of the
upper part of the volcanic edifice.

Only 14 seismic events were recorded during 31 October-1
November; most were located beneath the volcano with a few
in the Windy Hill and Fox~s Bay area. There were three long-
period events and several episodes of broadband tremor. A
small eruption at 1129 on 1 November caused ashfall within
the summit crater.

Information Contacts: Montserrat Volcano Observatory, Eifell
House, Olde Towne, Montserrat, West Indies.