Geologic Background:
Soufriere Hills volcano sits on the N flank of
the older South Soufriere Hills volcano, located at the S
end of Montserrat Island (13 x 8 km). The summit area
consists primarily of a series of ESE-trending lava
domes. Block-and-ash flow and surge units associated with
dome growth predominate in flank deposits.
Pyroclastic-flow deposits associated with the formation
of English's Crater have been dated at around 19,000
years BP (before present). A series of eruptions dated at
16,000-24,000 years BP pre-dates the Castle Peak dome in
the crater by an unknown period of time. English's Crater
is breached to the E. A radiocarbon date of ~320 ±
54 years BP from a NE-flank pyroclastic-flow deposit is
significantly younger than other radiocarbon dates from
the volcano, and could have resulted from the latest
activity of Castle Peak.
Historic Activity:
- There have been no reported historical eruptions, but
some undated deposits and the cone have a young
appearance.
- Periods of increased seismicity below Soufriere Hills
were reported in 1897-98, 1933-37, and again in
1966-67.
- Non-eruptive seismic swarms occurred at 30-year
intervals in the 20th century, but the first
well-documented historical eruption occurred in
1995.
Recent Activity:
- Seismicity had been elevated since August 1992, and
an earthquake swarm began on July 14, 1995. On July 18,
villagers around Soufriere Hills volcano reported
unusually loud rumbling noises coming from the fumarolic
areas, light ashfall, and a strong sulfur odor. On July
19, explosions were reported from a vent within the
summit crater between Chance's Peak and the Tar River
area. Seismicity and minor phreatic explosions continued
in the following days. On July 28, a second vent opened
SW of the original fissure vent and by July 30 the
original vent was inactive. Activity continued only at
Vent 2 until Aug. 11 when Vent 1 reactivated. An ash
explosion on Aug. 20 formed a third vent in the summit
crater and promped evacuation of up to 5,000 people.
Aerial reconnaissance on Aug. 24 showed a NNW-SSE
trending line of several small explosion craters in the
summit crater, with Vent 1 at the north end and Vent 3 at
the south end; Vent 2 was offset to the SE. Vent 4 formed
on the NNE flank of the Castle Peak dome on Aug. 27.
Seismicity and phreatic eruptions continued into
September and on Sept. 25 a lava dome began growing near
the linear chain of vents. Vent 5 formed on Oct. 11. Vent
6 formed on Oct. 14. Vent 7 formed on Oct. 18.
- Dome growth, ash eruptions, dome collapse and
pyroclastic flow continued from Nov. 1995 through July
1998.
- Additional pyroclastic flows from December 1998
through June 1999.
- Major dome collapse in July 1999. Followed by dome
growth through the remainder of 1999 to October 2000.
Rock falls and pyroclastic flows also occurred.
- Dome growth, rockfalls, and pyroclastic flows
continued through July 2001
Data Sources:
- Global Volcanism Network (V. 20, No. 6 to V. 26, No.
2).
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