A newly released geologic map and U.S. Geological Survey Professional Paper, Eruptive History of Mammoth Mountain and its Mafic Periphery, California, by CalVO scientists Wes Hildreth and Judith Fierstein recount the geologic and volcanic history of the area east of the Sierra Nevada in greater detail than any previously published report. The map includes the Long Valley Caldera, Mono-Inyo chain, Mammoth Mountain and the Middle Fork canyon of the San Joaquin River, including Devils Postpile National Monument.
Geophysical unrest beneath the Mammoth Mountain volcano, and in adjacent parts of the Sierra Nevada and Long Valley Caldera, has generated some concern among residents, stakeholders, and geoscientists since at least 1980 when four magnitude-6 earthquakes shook the area. Three decades of volcano monitoring near Mammoth Mountain has documented numerous earthquake swarms, ground deformation, and emission of magmatic carbon dioxide gas . The new map and publication contribute detailed information to scientists' understanding of the eruption frequency and volcanic history of the area, which is essential for assessing the region's likely long-term future volcanic activity.
The new map and report represent a significant milestone after decades of geologic fieldwork and research. The release of the map and report coincides with the 2016 celebration of the 100th anniversary of the establishment of the National Park Service. In the month of July, staff from the USGS, Devils Postpile National Monument and Inyo National Forest have teamed up to offer outdoor educational activities for the public as the new map and report are unveiled. CalVO geologists Wes Hildreth, Judy Fierstein, and others will be hosting an interpretive talk at Minaret Vista Overlook near the monument on July 14. They will also lead an interpretive hike to the Devils Postpile formation and to nearby Rainbow Falls, both in the monument, on July 15. If you plan to visit Devils Postpile National Monument this week, be sure to check out these great opportunities to hear about the volcanic history of the area from expert geologists!
Summer has arrived, and for many CalVO scientists, so has the season of fieldwork. During the fall, winter and spring, many of California's volcanoes are covered with snow, and challenging weather conditions make fieldwork difficult and time consuming. However, from May through October, warmer weather with minimal precipitation make it easier for scientists to access most of the volcanic places that are inaccessible during the rest of the year. Plans this season include spending weeks in the Long Valley Caldera mapping the geology; traveling around the state to collect hydrothermal water samples and service volcano monitoring equipment; and climbing the flanks of many volcanoes to collect rock and gas samples.
Scientists recently returned from climbing up to about 14,000 feet of elevation to the summit of Mount Shasta where they collected gas samples and temperature data. They used vacuum-sealed glass bottles to collect the gas samples then carefully packaged the bottles and carried them down the mountain. The volcanic gas samples contained in the bottles were taken back to the lab at CalVO to be analyzed.
Each sample must have less than 1% air contamination in order for it to be a good sample to use for analysis of the volcanic gases. Fortunately, one of the samples collected had no detectable (less than 0.01%) air contamination, so it was a great sample to measure—the climb up Mount Shasta and back down again was a success! We're looking forward to other successful fieldwork throughout this season.
New research by scientists at CalVO indicates that Ubehebe Craters formed about 2100 years ago during a single eruptive event. Ubehebe Craters are a lone cluster of volcanic craters in the northern half of California's Death Valley National Park. CalVO geologists Judy Fierstein, Wes Hildreth, and Duane Champion investigated the sequence of rocks to determine whether the 15 craters formed as several independent eruptions over hundreds of years from a long-lasting, deep magma source, or whether they formed at one time.
The scientists are confident that the craters are monogenetic—created during one explosive episode when magma interacted with groundwater, over several days, weeks or months (but certainly not over hundreds of years). Their evidence: first, dozens of layers of rocks ejected during successive eruptive pulses are "conformable"—no time is represented by erosion or anything else between them, so all layers must have fallen during a short-lived eruption sequence. Second, they note that the composition of basaltic cinder samples does not vary—meaning that a single batch of magma fed the multi-crater phreatomagmatic episode. Third, measured paleomagnetic directions are almost exactly the same; again, not much time could have passed between crater-forming pulses.
Short-lived eruptive sequences like the ones that formed Ubehebe Craters are common in volcanically active areas (for example, throughout the Cascade Range). This is the only young volcano in Death Valley National Park, which was otherwise a volcanically quiet area for the last million years. The new research will be presented at the 2016 Geological Society of America Cordilleran Section meeting at the beginning of April.