Estimating Eruption Model Input Parameters From Direct Observations of Deeply Eroded Basalt Conduits, San Rafael, UT

点击翻译按钮获取中文摘要

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)." Volcanoes create hazards for millions of people worldwide, including many living in parts of the USA. Scientists can now forecast the timing of many eruptions at well-monitored volcanoes. Unfortunately, it is currently not possible to accurately forecast how explosive an eruption might be, because this depends on a large number of factors, such as the shape of volcano conduits and the composition of magma, most of which depend on processes operating in the deep subsurface and so are not directly observable prior to eruptions. Better forecasts depend upon improving our understanding of the conditions that govern magma flow within volcanic conduits in the subsurface. This project aims to provide crucial data to improve this understanding through investigation of the geology of deeply eroded ancient volcanoes in the San Rafael desert of southern Utah. This unique geologic environment, where volcanoes have not erupted in millions of years, provides essential insight about processes operating in the subsurface during volcanic eruptions. We cannot observe these processes directly at currently erupting volcanoes, but we can interpret them from the features preserved in the geologic record. Connor, Wetmore and colleagues will combine geologic mapping with 3D terrestrial LiDAR imaging, geochemistry and petrological modeling, and analysis of the elastic properties of host rocks to develop a detailed understanding of the erosion and mixing processes that controlled formation of volcanic conduits of the San Rafael desert. The basic goal of making these observations is to place geological and geochemical constraints on a set of input parameters common to models of conduit flow and volcanic eruptions. This will be accomplished by: (1) generating 3D models of individual volcano conduits through geologic mapping utilizing terrestrial LiDAR. This will essentially bring conduits into the computer and allow the project team to measure cross-sectional areas, shapes, and change in radius with height, direct measures of conduit geometry needed in numerical models of conduit flow and development. This approach will allow study of the detailed 3D relationships between dikes and conduits, and breccia (host rock - magma) mixing zones, among other features in sufficient detail to be useful in conduit models. (2) Detailed textural and geochemical analyses of samples systematically collected from these conduits will yield insights into variations in mineralogy and chemistry of magmas across and along conduits. These data will constrain eruption parameters used in models, such as magma temperature, initial volatile content (obtained from melt inclusions in primary mafic minerals), viscosity, depth of crystallization, and across conduit gradients in these parameters. (3) The properties of the wall rock that hosts conduits will be carefully described. This description will include microstructural studies aimed at quantifying deformation mechanisms, strain type and intensity in the wall rocks, as a function of distance from the conduits.