Newberry Volcano Field Trip
Newberry Volcano and its surrounding lavas cover about 3,000 square kilometers in central Oregon. This massive, shield-shaped, composite volcano is located in the rear of the Cascades Volcanic Arc, ~60 km east of the Cascade Range crest. Lava compositions range from basalt to rhyolite. Eruptions began about half a million years ago and built a broad composite edifice that has generated more than one caldera collapse event. At the center of the volcano is the 6- by 8-km caldera, created ~75,000 years ago during a major explosive eruption. A significant mafic eruptive event about 7,000 years ago erupted lavas over a distance of 35 km from south of the caldera to Lava Butte. Newberry’s most recent eruption took place about 1,300 years ago in the center of the caldera and produced tephra and lava of rhyolitic composition.
On this field trip we will discuss the eruptive history and a wide range of eruptions of the volcano. We will visit a variety of locations, all of which are described in Jensen, R. A. and Donnelly-Nolan, J.M. (2017) Field-trip guide to the geologic highlights of Newberry Volcano, Oregon, in Field-trip guides to selected volcanoes and volcanic landscapes of the western United States. U.S. Geological Survey Scientific Investigations Report 2017-5022.
Estimated total walking distance: could vary depending on desires of group, less than a half mile to 2 miles, if trails at Big Obsidian Flow and Lava Butte are walked. The trip is appropriate for all levels of geologic background.
Julie Donnelly-Nolan is a geologist at the U.S. Geological Survey in Menlo Park CA. Her work involves field-based research on volcano histories and hazards. She is currently leading a long-term study of Newberry Volcano with the goal of understanding what this largest Cascades volcano has done in the past and what it might do in the future. In addition to her geologic mapping of the 1200-squre mile volcano, she works with a variety of collaborators including Bob Jensen of COGS. She also worked at Medicine Lake volcano in northern California where publications include the geologic map (https://pubs.usgs.gov/sim/2927/) and hazards assessment (https://pubs.usgs.gov/sir/2007/5174/a/). She did her PhD thesis at UC Berkeley focused on geologic mapping and argon dating of the Clear Lake Volcanic Field in the California Coast Ranges.
Bob Jensen retired in 2005 from the Deschutes National Forest after 30 years as an engineering geologist. Between 1988 and 2005, he self published 4 field guides to Newberry Volcano and in 2015 a field guide to Newberry National Volcanic Monument. Since 2006, he has volunteered with the USGS as a field assistant for Julie Donnelly-Nolan working on the mapping of Newberry Volcano. In 2017, Bob published with Julie another field trip guide to Newberry Volcano that is online as USGS SIR-2017-5022-J2 (https://pubs.usgs.gov/sir/2017/5022/j2/sir20175022j2.pdf)
Central Oregon Geoscience Society
P.O. Box 2154, Bend, Oregon 97709