CAREER: Detailed distributions of tephra fall characteristics: insights into magma fragmentation and transport via volcanic plumes

Explosive volcanic eruptions produce ash clouds that can reach miles into the atmosphere. These plumes are the most far reaching of volcanic hazards. They can cause fatalities and disrupt air traffic, the global economy, and the climate. The characteristics of the ash control how far it travels and when and where it falls on the ground. Quantifying ash characteristics is thus crucial to understand, predict, and model volcanic plumes. This is central to warn likely affected areas and reduce impacts from eruptions. This research project aims at clarifying the links between ash and eruptive processes. It will combine traditional and new techniques and use eruptions in the US Cascades as case studies. Models of ash transport will integrate the results of this project. It will increase the precision and accuracy of ash cloud forecasting. The educational project will raise awareness among high-schoolers of volcanic eruptions and deposits. It will focus on high schools in rural and tribal areas in Oregon and Washington. Students will learn about volcanic deposits in their backyard via hands-on activities. They will share their new knowledge with their local community via a presentation. The project ultimately aims at raising high schoolers interest in STEM education and scientific research. Because of the subterraneous nature of the processes leading up to tephra formation and dispersal, our knowledge of eruptive mechanisms mostly relies on the interpretation of tephra characteristics collected after the eruption. Morphological and textural studies currently focus on a limited number of parameters analyzed, clast sizes, and/or sampling locations, thus preventing a full capture of the complexity of tephra deposits. This project will address these limitations by 1) assessing the importance of secondary fragmentation, which leads to a change of the size and shape of tephra after their initial formation in the conduit; 2) improving Tephra Transport and Deposition Models; and 3) streamlining and standardizing the analysis of tephra physical characteristics. Comparing tephra final characteristics with those of the products of primary fragmentation in the conduit of the volcano will establish the amount of secondary fragmentation occurring during the eruption and its control on plume height. Contrasting characteristics between eruptions spanning orders of magnitude in volume and mass discharge rate will enhance our knowledge of the links between eruptive parameters and eruptive products and outline new strategies to quantify eruption source parameters indispensable to predict and model plume behavior. Interpreting lateral variations in size, density, and componentry distributions will help decipher transport processes such as particle aggregation and rafting. Direct implementation of results into existing numerical models of tephra transport and sedimentation will improve forecast of volcanic ash cloud and ensuing tephra fall. 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.