Dr. Alexa Van Eaton has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at the U.S. Geological Survey and Arizona State University. This project aims to improve our ability to predict and respond to the hazards of explosive volcanic eruptions. Dispersal of fine volcanic particles injected into the atmosphere during these events pose wide-reaching threats to infrastructure and the environment. Given the strong national and international reliance on numerical predictions of volcanic cloud movement, this project focuses on introducing new, field-based observations of eruption dynamics into existing methods of ash dispersal modeling. Two key questions motivate this approach: (1) how does the nature of particle aggregation evolve with respect to measurable properties of volcanic clouds?; and (2) what is the role of eruption column instability and surface water interaction in controlling the vertical distribution of mass in the atmosphere?
The initial stage of the project targets assimilation of field data from volcaniclastic deposits and remote sensing archives from the well-documented eruptions of Redoubt, Alaska (2009) and Mount St. Helens, Washington (18 May 1980). These observations will be used to characterize the spatiotemporal impact of atmospheric feedbacks accompanying volcanic ash dispersal, and provide inputs for 3d simulations of eruption column development using a cutting-edge microphysical model known as ATHAM. Results will guide the design and deployment of a new generation ash dispersal model that can account for the impacts of ash aggregation and column instability in a fast-running, operational setting. In addition, Dr. Van Eaton will partner with the Cascades Volcano Observatory (USGS, Vancouver) and School of Earth and Space Exploration (Arizona State University) to develop tabletop exercises educating undergraduate students, K-12 geoscience teachers and TV broadcasters about responding to volcanic ash hazards in the event of an eruption.
Volcanic ash is the most widespread hazard of explosive eruptions, impacting aviation and infrastructure hundreds to thousands of kilometers downwind. Yet the airborne dispersal of fine ash is challenging to forecast due to processes like ash aggregation, which lead to clumping and early fallout. This project has supported international collaborative research into the atmospheric dynamics of volcanic eruption plumes, with the overall goal of improving our resilience to explosive volcanism. Significant findings include: Discovery of a 'hailstone' mechanism of volcanic ash aggregation. By examining the dynamics of the 2009 eruption of Redoubt Volcano in Alaska, using data from weather radar, 3-D numerical modeling, and microtextural analysis of the fall deposits, we have identified that hail formation can trigger ash aggregation directly within volcanic plumes. As ash rises into the upper atmosphere, water-coated particles stick together and freeze. Some aggregates are recaptured into warm, moist updrafts, where they accumulate new layers of wet ash. This process takes place rapidly, initiating within minutes of eruption and stripping much of the fine ash out of the atmosphere. Afterwards, the remaining, dilute cloud of ash is not readily detected by weather radar, but still hazardous to aircraft. These findings lead to an improved method of ash dispersal forecasting for powerful 'wet' eruptions, whereby models may reasonably assume that 95% of the fine ash (<250 microns) converts into larger aggregates at the source. Insights into ash dispersal from super eruptions. Model simulations of a Yellowstone super eruption highlight the important roles of ash aggregation and umbrella spreading in controlling ash transport. Radial expansion of the ‘umbrella cloud’ is known to push the ash in all directions, including upwind. Our work shows that the effects on ash dispersal are much greater than previously thought, indicating that umbrella spreading must be accounted for in models of high-intensity eruptions, including those in the geological record. New clues from the devastating 536 AD eruption, El Salvador. The Miraflores branch of Mayan civilization was wiped out by a major volcanic eruption, which is thought to have contributed to the 6th-century global climate anomaly known as the 'dry fog' or dust-veil event. Fieldwork and lab analyses undertaken during this project with colleagues from the UK and El Salvador provide clues into what happened during this eruption. Following interaction between magma and water from the overlying lake, wet aggregation in the atmosphere scrubbed out much of the fine ash and sulfur-bearing gases. Our findings raise new questions about whether this eruption would have been capable of causing such a significant climate impact on its own. Exploring volcanic lightning as a monitoring tool. Can volcanic lightning provide information about eruption behavior during volcanic crises? We compared 3-D numerical models of plume development and lightning patterns during ‘wet’ and ‘dry’ eruptive phases (Redoubt Volcano, Alaska, in 2009 and Eyjafjallajökull, Iceland, in 2010). Results show that a unique lightning signature arises when large amounts of external water are involved – we suggest that water phase changes and growth of volcanic hail lead to a ‘dirty thunderstorm’. These patterns are distinct from the lightning triggered by dry, lower-level eruption plumes, which may be useful for monitoring eruption development in near-real time via the World Wide Lightning Location Network (WWLLN). Microbe dispersal by explosive volcanism. New work has also been undertaken to identify the abundances and species of diatoms (algae microskeletons) that are picked up and dispersed by volcanic eruptions. By examining the diatom content of three major eruption deposits from New Zealand, we have found that hitchhiking microbes can provide an important record of environmental change in the lead-up and response to big eruptions, including possible species extinctions. Overall, this project has fostered partnerships amongst research institutions in the USA (e.g., U.S. Geological Survey, Arizona State University, NASA, University of South Florida) and international groups (University of Cambridge, Victoria University Wellington, Durham University, El Salvador Servicio Nacional de Estudios Territoriales), and enhanced data sharing and methods development through participation in an international Volcanic Column Model Intercomparison exercise. Research findings have been disseminated to a broad audience through a chapter in the Encyclopedia of Volcanoes (2nd Ed.) and mainstream media coverage by LiveScience, Scientific American and The New Yorker, for example. This project has broadened the participation of women in science by funding the senior thesis research of one undergraduate student, and contributing to the field studies of three participants in the Research Experience for Undergrads program at Arizona State University (3 out of these 4 students are women). The project has also supported public engagement with science by virtual mentoring of K-12 classes via social media and SAGANet.org, by training K-12 Earth Science teachers at the USGS Cascades Volcano Observatory, and by creating exhibits that demonstrate the physics of explosive eruptions (‘trashcano’) to members of the general public at ASU’s Earth and Space Exploration Day.
