This project will investigate the rheological and thermodynamic properties of hydrous dacitic to rhyodacitic lavas from Santiaguito volcano in Guatemala, which form block flows. These have the potential to remain mobile for months to years, and to extend great distances. They are significant hazards, and block and ash flows resulting from flow-front collapse have occurred both at Santiaguito and Unzen (Japan) in recent times. Results of this project will include measurements of the actual temperatures and water contents of silicic block-lavas at Santiaguito, and their viscosity and heat capacity as a function of chemical composition, temperature, and water content. These silicic compositions are particularly interesting because andesitic magmas do not form block lava flows, and we will determine whether there is a "critical melt structure" at which this rheological change occurs. The results will be applied directly to refine existing models for the emplacement of slow-moving block lava flows, and will also be used to develop a predictive model of the viscosity of hydrous (rhyo-)dacitic liquids based on configurational entropy theory, providing important data required for improving current physical and thermal models of magmatic and volcanic processes.
The work will be carried out in close collaboration with volcano observers in Guatemala (INSIVUMEH), and the aim is to provide them with an improved understanding of rheology and heat budgets related to block flow emplacement, contributing to improved hazard monitoring and prediction capabilities. Other broader impacts of this project include training graduate students in viscometry and calorimetry techniques, and establishing the first laboratory in the USA that will apply low-temperature viscosity measurement techniques to hydrous silicate liquids.
