EAGER: The Brittle and Extensional Origins of Structures on Silicic Lavas

West Virginia University Research Corporation, Morgantown WV

Investigators

Abstract

Understanding the duration and speed of lava flows is central to assessing the risks associated with volcanic eruptions, especially for communities built on the flanks of volcanoes. Years of observations at persistently erupting volcanoes like Kilauea (Hawaii) have produced a sophisticated understanding of fluidal, fast-moving basaltic lava flows; however, a similar level of understanding is absent for other types of lava. Eruptions of highly viscous, slow-flowing silicic lavas are common in the geological record but are infrequent at human timescales, and therefore poorly understood. Most of our understanding of silicic lava flow comes from studies of ancient lavas coupled with simulations using analogous, viscous materials like corn syrup. Analog models and analogous geological materials like ice (glaciers) and mud (mudflows) predict that silicic lavas will flow away from the volcanic vent and therefore, stretch and extend. This should be a primarily brittle process akin to the formation of crevasses on glaciers. However, studies of ancient lavas report compression and thickening of silicic lavas through ductile folding of the lava's upper surface. The style of deformation is important in constraining the internal temperature and gas content of the lava as brittle fracturing will potentially release over-pressured gas and lava, causing explosive eruptions throughout the duration of the lava's advance. Conversely, if lavas do indeed fold then they must flow much faster than anticipated and will advance down the volcano's flanks rapidly, endangering downslope communities. The results will be applicable to future eruptions of silicic lavas in eastern California, Oregon, at Yellowstone National Park, and elsewhere around the world. Several graduate students will be supported with this award, and will gain important experience in both field and modeling techniques. Observations at several silicic lavas and review of literature challenge the existing interpretation of silicic lava flows being folded during ductile flow. Silicic lavas at Medicine Lake and Newberry volcanoes in the Cascade volcanic chain of the western United States will be focus of the study. Lavas will be mapped to understand the structural evolution of their upper surfaces, paying attention to the presence or absence of folds and other structures associated with compression. If, as expected, structures are dominantly extensional in nature, for example fractures and crevasses, models associated with folding and compression will be revised. A small unmanned aerial system (sUAS) will be used to generate high-resolution maps of accessible parts of the upper surfaces and to generate three-dimensional models of the structures that can measured further in virtual reality. Structures such as folds and crevasses, and rock types will be mapped on the new sUAS base to and establish the types, orientations and magnitudes of deformation. The entire upper surfaces of the lavas will be mapped using LiDAR and satellite imagery to examine the distribution of the structures and deformation over larger areas, and to fill-in gaps between more detailed mapping. Together these data will produce a comprehensive structural model that describes the evolving flow of silicic lava from the vent to the margins, and integrates understanding of ancient lavas from analog models and fundamental theory. 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.