Stop 1: Crestview
Stop 2: Aeolian Buttes
Day 7: Sampling of crystal-rich, non-welded ignimbrite from the northern lobes
on Month: June 2016
on Day 6: Examining the volcanic-plutonic connection in the high Sierra
on A brief break from looking at volcanic deposits to investigate the volcanic-plutonic connection.
Day 5: Aeolian Buttes, Panum Crater and Mono Lake
on Spot 1: Aeolian buttes. One last pumice and lithic count on the lower, densely welded part of Ig2NWb. Crystal-rich pumice and basaltic lithics abound! As we moved up section towards the eroded bedrock highs made up of Cretaceous granite, the ignimbrite becomes poorly welded and contains sparse dacitic juvenile clasts and swirly pumices.
Stop 2: Panum Crater is a young tuff ring with an extensive crater-filling lava dome of made of obsidian and bread-crusted devitrified rhyolite. Incredible views of Mono Lake!
LUNCH BREAK: Time to learn the secret wonders of the Jeffery Pine…
Stop 3: Water sampling at Mono Lake – here at the south tufa preserve. What, not looking at rocks? No pumice count? Liz and Adam collect alkaline water for analysis of oxygen isotopes, pH, conductivity, and alkalinity.
Day 4: The North Side of the Caldera
on Stop 1: We started the day with an overview of the north side of the caldera from the lookout at Bald Mountain. We also had a chance to see what a volcanic eruption from the Mono Craters would look like, as a result of a fire near Mono Lake! Fortunately the fire was brought under control fairly quickly as a result of expert work by firefighters.
Stop 2 & 3: We put our newly acquired pumice and lithic counting skills to good use in examining the northern ignimbrites. The crystal-rich pumices are pretty amazing! Here we learned that crystal-poor Bishop rhyolite was erupted mainly from the southeastern vents, whereas crystal-rich material was erupted from the vents along the northern margin of the caldera. We also observed an increase in the proportion of lithic clasts made up of recycled rhyolitic tuff.
Can you spot the ignimbrite?
One of the prized mixed pumices.
Spot 4: Glass Mountain Obsidian (a group favorite)!
Artistic moment of the day…
Day 3: Pumice and Lithic Counts in Ig1Eb
on 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.
Day 2: Fall vs. Flow?
on Stop 1: The Chalk Bluffs, where students described individual fall horizons, identified key features, especially lithic types, and created stratigraphic columns. These then became the basis for the next stops where further stratigraphic relations provided additional clues as to the complexities associated with the eruption of the Bishop Tuff. Our goal was to provide field tools that can be used to decipher the intricacies of large caldera-forming eruptions.
Stop 2: The iconic Chalfant Quarry, where every person who visits the Bishop Tuff must go for two reasons: 1. To take their picture in front of the beautifully exposed fall and ignimbrite sequence; and 2. To understand that the simple model of fall-then-flow deposition during caldera-forming eruptions is a drastic oversimplification, as ignimbrite interfingers with fall unit F8 before the deposits of fall unit F9.
Stop 3: The plot (or in this case, the ignimbrite) thickens as one goes north closer to source. We also experienced the heatwave that was gripping southern California and the rest of the southwest (“Wow, look at this great layering in the shady areas…”).
Field Group on top of Mammoth Mountain
on 
Day 1: Geologic Overview of Long Valley Caldera
on Stop 1: Today was our first day in the Long Valley area. Our group, which includes undergraduate and graduate students and two professors, gathered into a van and took the gondola up to the summit of Mammoth Mountain. From there, we were able to get an excellent perspective on Long Valley Caldera and its relationship to Sierra Nevada range front faulting. We also discussed the Mono-Inyo Craters volcanic chain and the much older intracaldera fill deposits that make up the Minarets.
Stop 2: On our drive back to Mammoth Lakes, we stopped to learn about pumice fall deposits formed by explosive eruptions. We also pondered the origins of lithic-rich layers and discussed how identification of the different lithic clast types can be used to infer vent location. We collected several bags of lithics, and a later careful examination showed that there were at least 10 different compositional types in the deposit.
Stop 3: The third stop – Deadman Creek Dome – reveals the many wonders of magma mixing. Here, you can see crystal-poor rhyolite swirled around and within crystal-rich material.
