The CALIPSO Project at Soufrière Hills Volcano, Montserrat, BWI: Using Integrated Deformation Data to Constrain Magmatic Processes
Glen Mattioli University of Arkansas, Fayetteville
Barry Voight, Derek Elsworth, Dannie Hidayat Pennsylvania State University
Alan Linde, Selwyn Sacks Carnegie Institution of Washington
Peter Malin Eylon Shalev Duke University
Jurgen Nueberg University of Leeds
Steve Sparks University of Bristol
The “Caribbean Andesite Lava Island Precision Seismo-geodetic Observatory,” (i.e.CALIPSO) has greatly enhanced the geophysical infrastructure at the Soufrière Hills Volcano (SHV), Montserrat with installation of an integrated array of borehole and surface instrumentation at four sites. Each site has a Sacks-Evertson dilatometer, a three-component seismometer (~Hz to 1 kHz), a Pinnacle Technologies tiltmeter, and an Ashtech u-Z CGPS receiver with choke ring antenna. This sensor package is similar to that being installed at volcanoes in western North America as part of EarthScope.
Figure 1. Aerial photograph to the southwest showing the scar from the 2003 massive dome collapse of SHV and its pyroclastic flow-created delta deposits. Photo by B. Voight.
CALIPSO sensors recorded the collapse of the SHV lava dome on Montserrat in July 2003, the largest such event worldwide in the historical record (Mattioli et al., 2004). Dilatometer data show remarkable and unprecedented rapid (~600s) pressurization of a deep source. Voight et al. (2006) inferred an oblate spheriodal source with average radius ~1 km centered at 5.5 to 6 km depth. An overpressure of ~1 MPa, was attributed to growth of 1-3% of gas bubbles in supersaturated magma, triggered by the dynamics of dome unloading.
Pyroclastic flows entering the sea may cause tsunami generation at coastal volcanoes worldwide, but geophysically monitored field occurrences are very rare. Mattioli et al. (2007) reconstructed the process of tsunami generation and propagation during the prolonged, gigantic collapse of the SHV in 2003 using a combination of strain, seismic, and GPS data from the CALIPSO array.
Mattioli (2005) also reported that periods of surface uplift recorded by GPS at SHV correspond to an inflating, and subsidence, to a deflating Mogi source. Inverted depths are between 6 and 13 km, with the recent observations favoring a deeper source, supporting a temporal evolution of the mid-crustal pre-eruption storage zone from 1995 to 2005. Elsworth et al., 2008 modeled the surface deformation and surface efflux records from 1995 through 2007 assuming a vertically stacked array of two chambers at 6 and 12 km depth. They concluded that despite the episodic nature of the SHV eruption, melt was supplied to the base of the magmatic system at nearly constant rate and that the lower chamber was largely responsible for the surface deformation.