CMG: Studies of Sediment Gravity Flows
Pitman, E. Bruce Principal Investigator
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This project combines simulations of pyroclastic flows and surges and related gravity currents based on meshfree methods, together with modeling and analysis, all tested against lab and field data. The Least Squares Meshfree Method forms the core of a proposed particle-based computational method for simulations. Adaptivity - injecting new particle basis functions, increasing basis function order of approximation - will be introduced, allowing accurate resolution of free surfaces and other fundamental structures within the flows. Mathematical and computational modeling will extend the current Least Squares methodology to flows which are composed of a mixture of gas and grains, and to flows with significant thermal content. Mathematical analysis will elucidate the smoothing properties of the method, to ensure a robust and accurate simulation technology, and to enable translation of the method to other geophysical mass flow systems. Simulations will be validated against laboratory experiments, and its predictive efficacy tested against field results. In this way, mathematical theory and geological experiment together can develop a new approach to the mathematical modeling of geophysical flow systems. Pyroclastic flows are heavier-than-air gas-particle mixtures resulting from volcanic activity. Pyroclastic flows can travel at velocities from 10-100 m/sec, and can attain temperatures upwards of 1000 degrees C. Pyroclastic flows can have high density, and move down mountainsides and under water, or they can be of low density, and lift over mountains and across water. Because of their speed, temperature and volume, pyroclastic flows pose an enormous risk to populations within miles of the volcanic source. Evidence of their destructive power can be seen Mount St. Helens, WA, USA, Soufriere Hills Volcano, Montserrat, Mount Pinatubo, Phillipines, and Colima Volcano, Mexico, among other sites. Although pyroclastic flows and surges (basically a dilute pyroclastic flow) are carefully studied, a detailed understanding of the dynamics of the stratified, flowing material over natural topography is not in hand; predictive capability a scientifically-based assessment of what regions are at high risk is lacking. As scientists, it is important to be able to rationally assess risk and communicate the nature of that risk to local public safety officials. An interaction between science and society based on a clear understanding of the phenomenology leading to the construction of reasonable hazard risk maps will, hopefully, save lives. This program of mathematical and computational research, coupled with laboratory and field study, will better predict the speed and extent of pyroclastic flows and surges. These results will serve the public interest by aiding the production of trustworthy hazard risk maps.