NSF Award
2422517
The most impressive and potentially dangerous expression of volcanic activity on Earth – commonly referred to as super-eruptions – involves explosive eruption of hundreds of cubic miles of volcanic ash in a single event. Super-eruptions produce destructive, fast-moving mixtures of ash and gas that can flow more than 100 miles along the ground. These pyroclastic flows leave behind deposits of ash and pumice that are referred to as ignimbrites. Ignimbrites cool very slowly, requiring decades to centuries to release their heat. During prolonged cooling, the ash particles can stick together, deform, and completely consolidate to make a welded deposit. Although we have been fortunate to not experience a super-eruption during human history, they are certain to occur in the future. On the other hand, hundreds of these large ignimbrites are preserved in the geologic record. Ignimbrites preserve important clues about how super-eruptions work. They can also point to geothermal and mineral resources that are often associated with the volcanic systems. This project will advance our understanding of super-eruptions and the deposits they leave behind. This work will train a Ph.D. student in studying volcanic processes and deposits. The project will also include an undergraduate student who is from a historically underrepresented group in outreach activities with the Buffalo Museum of Science.<br/><br/>Despite the importance of large ignimbrites in helping to understand potential hazards and in locating resources, fundamental questions still need to be answered:<br/>• Do large-volume pyroclastic flows that travel long distances move in a manner akin to hot, turbulent flows with low concentrations (akin to super-intense sandstorms), or are they more like hot avalanches of concentrated ash particles? This is directly relevant for volcanic hazard mitigation.<br/>• Also relevant to hazards mitigation - how do the flows maintain high temperatures (between 1200-1800ºF) over distances of 50-100 miles or more? <br/>• How is the welding of a deposit (ignimbrite) produced and what is its quantitative relation with cooling and material properties of ash in the deposit? Such a quantitative understanding can aid in the interpretation of large ignimbrites related to natural resources.<br/>This project addresses these questions using as a case study the Peach Spring Tuff (PST), a well-preserved deposit that extends 80-110 miles to the east and west of its source volcano, which was located along the Arizona-California border (the volcanic system has recently been an active mining district). Flow- and deposition-related data will include deposit textures, sizes and types of ash, pumice, and other rock types, grading, internal contacts, and anisotropy of magnetic susceptibility. Welding- and cooling-related data will include deposit density, rock strength measured at outcrops, porosity, and permeability (both field and laboratory measurements), fracture characteristics, pumice deformation and other cooling-related textures, thermal remanent magnetism to estimate minimum temperature of the deposit, indicators of rate of cooling, and magma viscosity. Experiments will constrain the dependence of welding on pressure and temperature, aiming to produce a diagram showing conditions required to produce the observed PST properties and which can be applied to other deposits. Finally, computational modeling will use PST material properties to reproduce the thermal and welding history of the ignimbrite including the role of pore-gas pressure, with validation against the experimental results and other data related to emplacement temperature and cooling rate. The project will provide new insights into large-volume ignimbrites and welding in glassy volcanic materials, which has applications to a range of volcanic processes beyond ignimbrite welding, along with models that can be applied elsewhere. The results will inform our understanding of smaller-volume pyroclastic flows; these occur with greater frequency than large-volume eruptions, and as a result have significant hazards implications. This project will also: (1) train a Ph.D. student in application of field, experimental, and computational studies of volcanic processes and deposits; (2) provide internship opportunities for an undergraduate student in a STEM field who is from a historically underrepresented group; and (3) will be included in outreach activities such as with the Buffalo Museum of Science.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
