SOUFRIÈRE HILLS VOLCANO
A significant series of volcanic eruptions decimated
the southern half of Montserrat during the 1990s. Montserrat is an island
in the northern Lesser Antilles Volcanic Arc (eastern Caribbean Sea). The
islands of the Lesser Antilles have a volcanic origin, the result of the North
American Plate subducting westward & downward beneath the Caribbean Plate.
The Soufrière
Hills Volcano occupies much of the southern half of Montserrat. It is
a >31,000 year old, andesitic, subduction zone stratovolcano. Its
current phase of activity began in 1995 and 1996, prompting the evacuation of
most of the island's southern half. A significant ash eruption in summer
1997 destroyed the capital city of Plymouth along the southwestern shore of the
island. The eruption was apparently triggered by the injection of
basaltic magma into one of the volcano's two magma chambers. Soufrière
Hills has been erupting intermittently to the present day (including activity
in 2011), and the southern part of Montserrat has been off-limits to
residents. Many former Plymouth
residents have emigrated to Britain.
Montserrat - the Soufrière Hills Volcano is under the cloud cover in the southern
part of the island. The grayish-colored
areas are recent ash deposits.
(Satellite photos provided by TerraMetrics/Google Earth/DigitalGlobe)
Soufrière Hills Volcano andesitic lapilli & ash (field of view ~5.1 cm across) from a 1997
pyroclastic flow (maybe the 3 August 1997 flow?) that engulfed Plymouth, due
west of the volcano. This was collected from just inside a doorway of a
destroyed building in Plymouth. Collected & generously donated by
David Lea.
Soufrière Hills andesite lava (above & below; 9.6 cm across at its widest) -
this lava sample consists two lithologies, sharply demarcated (see boundary
line drawn below) and defined by a slight color change, a phenocryst
abundance/size change, and a vesiculation difference. The left portion of
the sample is light gray, semi-vesicular porphyritic andesite. The right
portion of the sample is a very light gray, pumiceous porphyritic
andesite. Available petrologic information indicates that 1997 Soufrière
Hills andesite is a quartz-bearing, two-pyroxene, porphyritic hornblende
andesite. Dominant phenocrysts include hornblende amphibole, hypersthene
pyroxene, and plagioclase feldspar. Minor phenocrysts include
titanomagnetite, quartz, and augite pyroxene microphenocrysts. The
groundmass material is a mix of finely-crystalline plagioclase feldspar,
orthopyroxene, augite clinopyroxene, pigeonite, titanomagnetite, and quartz, plus
rhyolitic glass.
Locality:
summit of Soufrière Hills Volcano, southern Montserrat, northern West Indies,
eastern Caribbean Sea.
Collected in June 1998 & generously donated by
Attila Kilinc.
Soufrière Hills Volcano andesite (field of view ~5.8 cm across) - close-up of sample
shown above. Light gray semi-vesicular andesite is to the left.
Very light gray pumiceous porphyritic andesite is to the right.
Soufrière Hills Volcano andesite (field of view ~3.6 cm across) - close-up of sample
shown above. This is very light gray pumiceous porphyritic andesite
showing large disrupted amphibole phenocrysts (black).
Soufrière Hills Volcano andesite ash (field of view ~5.1 cm across) - loose, very
fine-grained ash from a February 2006 eruption of the Soufrière Hills
Volcano. It was collected from the top of St. Georges Hill, just
west-northwest of the volcano (see satellite photos above). Collected
& generously donated by David Lea.