Chapter 5 Vulcanian explosions at Soufrière Hills Volcano, Montserrat between 2008 and 2010

Abstract

Vulcanian explosions generated at Soufrière Hills Volcano between 2008 and 2010 varied from simple events involving minimal pyroclastic density currents (PDCs) to complex events involving more than one explosion. Calculated volumes for the deposits of the PDCs formed by these explosions ranged up to 2.7×106 m3, with more than half the explosions having volumes greater than 1×106 m3. The deposits formed by the explosions varied in lithology, with some explosions generating pumice-rich PDCs (e.g. 29 July 2008 and 11 February 2010) showing development of sinuous lobes. These explosions are similar to those formed in 1997, with gas-rich, conduit-derived magma being the dominant driving mechanism. Other explosions were pumice-poor (c. 5 wt% pumice) and generated morphologically distinct PDC deposits. Many of the pumice-poor explosions were associated with lower tephra plumes of <8 km, but were some of the largest volume events in terms of PDC production and suggest a generation mechanism involving destruction of significant quantities of the lava dome. Analysis of video footage shows that PDC formation was pulsatory, probably related to destabilization of portions of the lava dome during the initial phases of the explosion.

Chapter 9 Thermal, acoustic and seismic signals from pyroclastic density currents and Vulcanian explosions at Soufrière Hills Volcano, Montserrat

“…Accordingly, the total discharged plume volume of 0.8 Â 10 6 -20.2 Â 10 6 m 3 is estimated by integrating the volume flux on the 22 s-long gas-thrust phase, that would give a total discharged mass of 5.4 Â 10 6 -272 Â 10 6 kg. This is in agreement with previous estimates using different methods from other Vulcanian eruptions at SHV (Druitt et al 2002;Formenti et al 2003;Komorowski et al 2010;Cole et al 2014).…”

“…This VLP seismic signal with a frequency of 0.04 Hz seems to be a typical feature of large Vulcanian explosions at SHV, at least in the 2008-2010 period (Cole et al 2014), but not previously reported. Nevertheless, ultra-low-period (ULP .100 s) seismic signals have been recorded by broadband seismometers at SHV (Green & Neuberg 2005) and explained as being related to the pressurization of the upper conduit, presumably by a trapped gas phase.…”

“…The vent area of the explosion was the western side of the lavadome summit. The largest PDC associated with this explosion reached the sea (run-out of .4 km) at Aymers Ghaut, and minor PDC activity (run-out of ,2 km) also occurred in several other valleys, including Tyre's Ghaut (Cole et al 2014).…”

“…9.6). The seismic signal associated with this event lasted approximately 7 min, sending a tephra column to an elevation of 7.3 km above sea level (asl) into the atmosphere (Cole et al 2014). Direct observations showed extensive ballistic fragments showering the northern and western flanks of the volcano up to distances of around 1 km.…”

An inclined Vulcanian explosion and associated products

“…Druitt et al 2002;Cole et al 2014;Wadge et al 2014). The explosions have occurred as isolated events, as part of month-long sequences, or associated with dome collapse events (Edmonds et al 2006;Loughlin et al 2010;Cole et al 2014).…”