Imaging Magma Under St. Helens

A primary goal of this work is to produce a geophysically constrained, quantitative image of the architecture of the Mount St Helens magmatic system useful for understanding how magmas enter, ascend through, stall, and interact with the crust. This model must be consistent with the distribution and compositions of volcanism in the region, the regional geologic structure, the longevity and consequent thermal structure of the Greater Mount St Helens magmatic systems. To these ends, geologists and geophysicists will work together in interpreting the geophysical results. Our aim is to produce a 3D model of the rock types, seismic properties, temperatures, and melt distributions through the crust, and possibly well into the mantle, available for download and use by other investigators. We plan to implement both simple text-based model files, as well as a netCDF based model exchange format, consistent with freely- available visualization tools provided by IRIS, as well as open source applications such as Paraview.

The project emphasizes multi-disciplinarity and integration to image the architecture of an active volcanic system with unprecedented resolution. We will collect many different seismic signals, including Vp and Vs from local tomography in the upper crust, Vp from the active-source imaging throughout the crust, Vs from ANT in the crust and uppermost mantle, information on anisotropy from splitting and receiver functions, and information on the nature and location of interfaces at a variety of wavelengths from receiver functions and from active-source imaging. These data will be jointly analyzed and interpreted with MT imaging, which reflects different physical parameters (electrical resistivity, electrical anisotropy, induction vectors that indicate locations of electrical current concentrations which may be attributed to sutures between crustal blocks or fluid/magma inclusions, etc.) of many of the same geologic structures, with thermo-barometry obtained from petrological studies, and regional geology and structure. Ways to integrate these methods will be sought - for example, as petrology will provide the typical depth range of reservoirs, seismic imaging provides good constraints on the locations of boundaries, while MT constrains properties such as fluid fraction and connectivity, temperature and tectonic fabric (see http://www.calcul.isto.cnrs-orleans.fr/sigmelts/). Those properties are also relevant to how melt affects seismic observables.

In reaching our goal (3D structure of the crustal column underneath Mount St Helens), we will provide the community with the best available initial conditions to test hypotheses of magma generation, transport and evolution in the mantle and crust (See questions listed in the introduction section) with forward numerical models. These models will be able to include of an accurate thermal and rheological structure to the mantle and crust, allowing us to quantify where magma crystallization and partial melting occurs in the magmatic column, and what is the geometry of those magma bodies.