Pocket Basin: Just how explosive was it?
Category: Research Poster
Author(s): Jason Green, Lauren Harrison
Presenter(s): Jason Green
Mentors(s): Lauren Harrison
The Lower Geyser Basin in Yellowstone National Park features many thermal features, including hot springs, geysers, and mud pots. Hydrothermal explosions are violent events when water flashes to steam and brecciates surrounding rock, sending ejecta flying and forming craters. Pocket Basin is a crater ~800 m long and 370 m wide, hypothesized to have formed by a large hydrothermal explosion ~13,000 years ago. A large primary explosion formed the crater, but many smaller explosions have likely occurred based on the oblong crater shape. This project determines the number of potential hydrothermal explosion events using variations in hydrothermal breccia grain size, composition, and geochronology. Sixteen samples were collected around the crater rim and dried for 24 hours before sieving samples into six grain sizes, ranging from 6.3 mm to 250 μm. Grain size distributions showed a variable difference between the amount of clays and larger clasts. Spatial variations in grain-size distribution around Pocket Basin support multiple explosion events, which we will test by selecting representative samples for componentry analysis. Clays will be identified using X-ray diffraction to constrain temperatures of hydrothermal alteration in different explosion pulses. These results will then be interpreted with context provided by optically stimulated luminescence dates. We hypothesize that a series of explosions occurred in Pocket Basin, suggesting a longer-term hazard may be present in explosive hydrothermal areas. Because hydrothermal explosions pose an ongoing threat to human safety in Yellowstone National Park, constraining the probability of future events in historically active regions is critical.