Chapter 1 An overview of the eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010

Abstract

Abstract:The 1995-present eruption of Soufrière Hills Volcano on Montserrat has produced over a cubic kilometre of andesitic magma, creating a series of lava domes that were successively destroyed, with much of their mass deposited in the sea. There have been five phases of lava extrusion to form these lava domes: -March 1998-July 2003 August 2005-April 2007July 2008-January 2009 and October 2009-February 2010. It has been one of the most intensively studied volcanoes in the world during this time, and there are long instrumental and observational datasets. From these have sprung major new insights concerning: the cyclicity of magma transport; low-frequency earthquakes associated with conduit magma flow; the dynamics of lateral blasts and Vulcanian explosions; the role that basalt-andesite magma mingling in the mid-crust has in powering the eruption; identification using seismic tomography of the uppermost magma reservoir at a depth of 5.5 . 7.5 km; and many others. Parallel to the research effort, there has been a consistent programme of quantitative risk assessment since 1997 that has both pioneered new methods and provided a solid evidential source for the civil authority to use in mitigating the risks to the people of Montserrat.At the time of writing (January 2013), the Soufrière Hills Volcano (SHV) is in its 17th year of eruption, placing it with a select group of very long-lived eruptions from silicic volcanoes. Within the Caribbean plate, only two other silicic volcanoes have had longer-lived historical extrusive eruptions: Santiaguito, Guatemala (1922( -present: Harris et al. 2003 and Arenal, Costa Rica (1968 -present: Wadge et al. 2006). As with both of these volcanoes, SHV has not extruded lava continuously for the whole eruption, but has erupted intermittently. In fact, it has been extruding lava for a cumulative total of only 8.5 years out of 17. So in what sense can we consider this a single eruption rather than a series of shorter ones? The longest gaps between extrusive phases have been about 2-3 years (July 2003-August 2005 February 2010-present). However, during the pauses between extrusion at SHV, there have been many indications that the volcanic system remains active. These have included inflation of the island's surface, the release of volatiles in quantities similar to those seen during lava extrusion, swarms of low-frequency seismicity, explosions and the production of ash. This suggests that there are processes within the system responsible for producing alternating extrusive and non-extrusive states. Melnik & Sparks (2005) showed theoretically how non-linear response to relatively minor perturbations of the magmatic system can result in such behaviour.Recognition of the long-term continuity of the eruption process has direct consequences for the tasks of monitoring and estimating the risks posed by the volcano. It means that the Montserrat Volcano Observatory (MVO) must monitor the volcano continuously, even during periods of relative quiescence and apparent inactivity. The probabil...

Volcano Seismology: Detecting Unrest in Wiggly Lines

“…Low frequency families of seismicity identified during this unrest period at Soufrière Hills volcano were followed by a dome collapse on 25 June 1997. Soufrière Hills Volcano was chosen by the VUELCO project as a target volcano due to the longevity of its dome building and collapse cycles which have been ongoing since 1995, providing a wealth of associated geophysical data (Sparks and Young 2002;Wadge et al 2014). In total, 11 distinct seismic sources (i.e.…”

The Variability of Refractivity in the Atmospheric Boundary Layer of a Tropical Island Volcano Measured by Ground-Based Interferometric Radar

“…Montserrat (17 • N, 62 • W) is a small (16 km × 10 km) tropical island with a wet season (July-November) and a typical surface temperature range from 24 to 33 • C. Measurements on 4-5 August using the GPRI were made from the Montserrat Volcano Observatory site (MVO; elevation 279 m a.s.l.) towards Soufrière Hills Volcano, which dominates the southern part of the island and produced a long, complex eruption between 1995 and 2010 (Wadge et al 2014) (Fig. 1).…”

Communication Demands of Volcanic Ashfall Events

“…Despite this, ongoing ashfalls, acid rain and gases intermittently affected populated areas of this small island (e.g. from November 2009 to February 2010), and continued for prolonged periods of time (Wadge et al 2014). Communication strategies for managing ashfalls have developed and improved over time, creating both formal (often broadcast via radio) and informal local information networks.…”