Collaborative Research: An Integrated Study of Silicic Lava Emplacement

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Understanding the duration and speed of lava flows is central to volcanic hazard management and risk assessment. Years of observations at persistently erupting volcanoes like Kilauea (Hawaii) and Etna (Sicily) have produced a sophisticated understanding of basaltic lava flows; however, a similar level of understanding is absent for other types of lava. Eruptions of viscous, silicic lavas are common in the geological record but are infrequent at human timescales. Observations of active silicic lavas and their behavior are thus very limited. Two eruptions of a particularly viscous lava called rhyolite in the 2000s in Chile, allowed the first real-time observations of rhyolite lava eruptions. Those observations have led to the need for volcano scientists to re-examine the ways that silicic lavas flow because they were seen to be faster and flow for longer durations than anticipated. In this study, two very young rhyolite lava flows in California will be the focus of a detailed study in which their internal and external structures and cooling history will be examined in order to better understand how they flowed, for how long, and how fast. The results will be applicable to future eruptions of rhyolite lava in eastern California, Oregon, at Yellowstone National Park, and elsewhere around the world.Obsidian Dome and South Coulee lavas will be the focus for exogenous and endogenous growth patterns using structural architecture and strain, thermal, and rheological gradient patterns. The researchers will compile a detailed morphological map using LiDAR data and three-dimensional structural analyses using macroscopic features in the field and microscopic strain studies. The analyses will characterize and quantify the types and magnitudes of strain active in different parts of the lavas throughout stages of their eruption and emplacement. Strain datasets will then be integrated with the results of cooling rate analyses from spherulites and differential scanning calorimetry to constrain the emplacement timescales. Rheological experiments will quantify the variations in effective viscosity due to variations in crystal, bubble, and dissolved water contents. Together these data will produce a comprehensive structural and thermo-rheological model that describes the evolving flow of silicic lava from eruption to cessation, and from the vent to the margins.