Montserrat - Soufrière Hills
Montserrat is one of the Lesser Antilles Islands, an archipelago in the Caribbean Sea, north of South America. Many of the islands are volcanic, and their location roughly traces the edge of the Caribbean Plate along its boundary with the tectonic plates (North and South American Plates) beneath the Atlantic Ocean. The Caribbean Plate is overriding the North American Plate. As the plates collide, the mantle of the overriding Caribbean Plate melts, generating magma that rises to the surface and feeds Soufrière Hills and other volcanoes in the Lesser Antilles.
The Soufrière Hills, a volcano on the island of Montserrat, in the Lesser Antilles island chain in the Caribbean Sea, has been active since 1995. Soufriere Hills is a stratovolcano—a steep-sloped volcano comprised of alternating layers of hardened lava, solidified ash, and rocks ejected by previous eruptions. Aside from a seventeenth-century eruption, the volcano was mostly quiet during historical times. The volcano’s activity heightened in 1995, forcing the temporary evacuation of the southern half of Montserrat and the permanent abandonment of the capital city of Plymouth.
An area around the volcano, containing about two-thirds of the island, is vulnerable to volcanic hazard and is a no-go area. Around 40% of the island is unaffected by volcanic activity but these areas may be prone to ash falls and volcanic gases during any volcanic activity and if the wind is blowing from south to north. These sometimes cause cancellation of flights to and from the island.
In addition there are three areas around the coastline which are designated Maritime Exclusion Zones where no shipping should enter. The largest of these extends for 4km on the eastern side of the island and there are two on the western side of the island. The most southerly of the two extends for 2km off shore and the third for a half kilometer off shore.
An island-wide siren system is installed to warn of volcanic activity. The sirens are tested daily at 12:00 midday. If the sirens sound outside this, tune to Radio Montserrat (ZJB) immediately on FM 88.3 or 95.5 for an accompanying message. The radio station also provides regular scientific updates and advice to listeners.
The volcanic eruption which devastated Montserrat began on 18 July 1995. By 26 December 1997, when the most extreme explosive event occurred, approximately 90% of the resident population of over 10,000 had had to relocate at least once and over two-thirds had left the island. Virtually all the island’s important infrastructure was destroyed or put out of use. The private sector collapsed and the economy became largely dependent, directly or indirectly, on British aid funding public sector and related activities. The total capital loss was unofficially estimated as up to £1 billion, mostly only partially recoverable or uninsured. Much of this relates to residential real estate. In November 1999, after 18 months of apparent quiescence, there was another upsurge in volcanic activity. This underlinef the need for careful monitoring, risk management and the difficulties of planning rehabilitation.
At 11:27 p.m. local time on July 28, 2008, the Soufriere Hills Volcano on the Caribbean island of Montserrat experienced a partial dome collapse. Explosions from the dome accompanied the event, and the resulting volcanic ash column reached an estimated 12 kilometers (40,000 feet) in altitude. No injuries were reported, but nearby residents temporarily evacuated the area. Volcanic material fell on the abandoned city of Plymouth, Montserrat’s former capital, which had been destroyed by earlier eruptions.
A recent eruptive phase of the volcano began with a short swarm of volcano-tectonic earthquakes — earthquakes thought to be caused by movement of magma beneath a volcano — on October 4, 2009, followed by a series of ash-venting events that have continued through October 13, 2009. These venting events create plumes that can deposit ash at significant distances from the volcano. In addition to ash plumes, pyroclastic flows and lava dome growth have been reported as part of the current eruptive activity.
While much of the island is covered in green vegetation, gray deposits that include pyroclastic flows and volcanic mudflows (lahars) are visible extending from the volcano toward the coastline. When compared to its extent in earlier views, the volcanic debris has filled in more of the eastern coastline. Urban areas are visible in the northern and western portions of the island; they are recognizable by linear street patterns and the presence of bright building rooftops. The silver-gray appearance of the Caribbean Sea surface is due to sunglint, which is the mirror-like reflection of sunlight off the water surface. The sunglint highlights surface wave patterns around the island.
In the waning days of 2009 and the first days of 2010, the lava dome on the summit of Soufrière Hills Volcano continued to grow rapidly. As the dome rises, rocks and debris can break off, cascading down the river valleys and gullies that radiate from the summit. These pyroclastic flows are among the major hazards created by Soufrière Hills.
A massive eruption of Montserrat’s Soufrière Hills Volcano covered large portions of the island in debris. The eruption was triggered by a collapse of Soufrière Hills’ summit lava dome on February 11, 2010. Pyroclastic flows raced down the northern flank of the volcano, leveling trees and destroying buildings in the village of Harris, which was abandoned after Soufrière Hills became active in 1995. The Montserrat Volcano Observatory reported that some flows, about 15 meters (49 feet) thick, reached the sea at Trant’s Bay. These flows extended the island’s coastline up to 650 meters (2,100 feet).
On February 21, the drainages leading down from Soufrière Hills, including the White River Valley, the Tar River Valley, and the Belham River Valley, were filled with fresh debris. According to the Montserrat Volcano Observatory, pyroclastic flows reached the sea through Aymers Ghaut on January 18, 2010, and flows entered the sea near Plymouth on February 5, 2010.
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