Institution: Penn S, U of Ark, Carnegie Inst of W, Duke
Sponsor: NSF
Start_Date: 11/1/2002
End_Date: 4/30/2003
Lat: 16.75
Long: -62.125
Descr: The ongoing eruption of the Soufriere Hills Volcano on Montserrat provides an unprecedented opportunity to investigate complex magmatic processes at an andesitic volcano. Growth of the lava dome has been unsteady and accompanied by variable, frequently cyclic patterns of ground deformation, seismicity, pyroclastic flow generation, and explosive eruptions. The cycles occur on several scales, including a short-term scale (~6- to 18-hour), a meso-term scale (~7 weeks), and a long-term scale (~30y) (Voight et al., 1998, 1999). The cycles provide insights into the magma-flow and eruption dynamics at andesite volcanoes, with the short-term cycles suggesting that degassing, rheological stiffening of the magma, and pressurization in the upper parts of volcanic conduits are coupled and control many of the geophysical and dynamical phenomena observed (Voight et al., 1999; Melnik and Sparks, 1999). The meso- and long-term cycles, we propose, reflect deep-seated processes involving the ! magma reservoir (Mattioli et al., 2000; Voight and Elsworth, in prep.). We propose to investigate the dynamics of the full system using an integrated array of specialized instruments in a series of four strategically located 200-m drill holes, and several shallower holes, surrounding the Soufriere Hills volcano. We argue that the system is still active and dynamic enough (and will remain so for the foreseeable future) to merit the additional investment of the geoscience community. Analysis of the continuous data provided by these instruments should provide new insights, and specific constraints to theoretical models, involving the dynamic behavior of the magmatic system. The instrument package for each deep hole, designed to have long life at high temperatures, will include a downhole dilatometer and a seismometer, with a surface CGPS station. The observatory will be fully integrated into the surface monitoring networks operated by the Montserrat Volcano Observatory (MVO) and the University of Puerto Rico (UPRM), and will be used to track processes occurring in the active magma reservoir and its associated conduit systems. We will employ a new version of the Sacks- Evertson borehole strainmeter that will operate with long life (decades) under conditions of high temperature. Dilatational strains, even from relatively small changes in the reservoir system, will be detectable. Recordings of earthquakes by the borehole sensors will provide very broadband data (0 Hz to 1 kHz) for study of the seismic sources. Passive seismometers at the depths proposed will have very low noise levels and enable detection of very small earthquakes. These instruments will allow probing the changes in the andesitic volcanic system with unprecedented sensitivity. Additional holes will house very high-gain tiltmeters. Previous work at other volcanoes has shown that such high sensitivity information is essential to our understanding of the physics of magma reservoirs, but little work has been done on andesite stratovolcanoes and the results of our work should be valuable as a model for other sites. Obvious is the societal value of high sensitivity measurements with potential for early warning of unrest. This is a collaborative project involving PIs from Penn State University, Carnegie Institution of Washington (CIW), University of Arkansas, and University of Bristol, UK. An integrated work plan subdivides the project into equipment fabrication and installation, data acquisition, numerical modeling, analysis and communication of results. Project coordination is the responsibility of B. Voight (PSU). Installation of the permanent observatory instruments will be controlled by I. Selwyn Sacks and A.T. Linde (CIW), with contributions by P.E. Malin (Duke). Operation of the CGPS network, and GPS analyses, will be guided by G.S. Mattioli (UARK), and integrated with data monitored by the Montserrat Volcano Observatory (MVO).
