Cordilleran Section - 117th Annual Meeting - 2021

Paper No. 14-14
Presentation Time: 11:05 AM


HARRISON, Lauren, U.S. Geological Survey, Volcano Science Center - CalVO, 345 Middlefield Road, Menlo Park, CA 94027, HURWITZ, Shaul, US Geological Survey MS 439, 345 Middlefield Rd, Menlo Park, CA 94025-3561, STELTEN, Mark E., USGS, California Volcano Observatory, 345 Middlefield Road, Menlo Park, CA 94025-0000, CHURCHILL, Dakota, 10887 Macouba Pl, San Diego, CA 92124-2049 and HUNGERFORD, Jefferson, National Park Service, Yellowstone Center for Resources, Yellowstone National Park, WY 82190

It is well documented that phreatic explosions of shallow hydrothermal systems can be triggered by the sudden release of pressure caused by mass wasting events. However, many questions remain about the details of the relationship between the two processes including how external conditions such as deglaciation impacts these systems. An excellent place to investigate the interplay of these factors is Yellowstone’s hydrothermal system, which has been active through recent glacial epochs (e.g., Bull Lake ~150-140 ka and Pinedale ~22-13 ka) and exhibits small (<2 m) and large (>2 km) phreatic craters. We focus on Pocket Basin and Twin Buttes, two large craters in the Lower Geyser Basin, one of Yellowstone’s largest and most active thermal areas. LiDAR 0.5-meter resolution elevation data collected in 2008 is used to analyze the volume of material excavated by the explosions, extrapolate ground surface morphology before the explosions, and estimate deposit thickness of explosion breccia. The Pocket Basin explosion crater is a 365- by 800-meter depression with shallowly dipping inner slopes and an asymmetric hydrothermal breccia deposit ringing the crater. It was modeled as a simple explosion. Twin Buttes explosion crater is roughly circular with a circumference of ~645 meters and contains multiple smaller nested craters. The deposits surrounding Twin Buttes can be attributed to two sources: 1) a large hydrothermal explosion with angular breccia fall deposits and 2) a water-rich landslide that rafted meter-sized boulders far from their original position. We modeled Twin Buttes both as a hydrothermal explosion with a surge deposit and as a landslide followed by an explosion. Preliminary results support a link between a landslide and a hydrothermal explosion, as does a comparison with Pocket Basin. These results will be supported by future geochemical and geochronological analysis to differentiate between deposits from different emplacement processes.