Stops 1 & 2: Today students learned the virtues of detailed pumice and lithic counts for revealing the intricate dynamics of an eruption. Between the first and second stops, students were able to demonstrate a substantial change in the average crystallinity of pumice clasts by counting ~100 clasts at each locality. The goal was to understand the ways in which you can distinguish geologically complicated units by systematically quantifying pumice and lithic types. The first site also had spectacular examples of fumarolic degassing pipes.
Stops 3-5: The next stops were in the Owens River Gorge, where we discussed how pyroclastic flows interact with the pre-existing topography. We also learned to recognize different welding packages and distinguish between flow breaks and time breaks through a clever method of pairing stratigraphic relations with detailed density measurements (Wilson and Hildreth 2003).
Radiating columnar joints in the welded portion of Ig1Eb ignimbrite in Owen’s Gorge.
Adam and Liz excited to learn about the Wilson welding scale.