Field-trip guide to the geologic highlights of Newberry Volcano, Oregon

Scientific Investigations Report 2017-5022- J2
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Abstract

Newberry Volcano and its surrounding lavas cover about 3,000 square kilometers (km2) 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. The volcano overlaps the northwestern corner of the Basin and Range tectonic province, known locally as the High Lava Plains, and is strongly influenced by the east-west extensional environment. 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 when a major explosive eruption of compositionally zoned tephra led to caldera collapse, leaving the massive shield shape visible today. The volcano hosts Newberry National Volcanic Monument, which encompasses the caldera and much of the northwest rift zone where mafic eruptions occurred about 7,000 years ago. These young lava flows erupted after the volcano was mantled by the informally named Mazama ash, a blanket of volcanic ash generated by the eruption that created Crater Lake about 7,700 years ago. This field trip guide takes the visitor to a variety of easily accessible geologic sites in Newberry National Volcanic Monument, including the youngest and most spectacular lava flows. The selected sites offer an overview of the geologic story of Newberry Volcano and feature a broad range of lava compositions. 

Newberrys most recent eruption took place about 1,300 years ago in the center of the caldera and produced tephra and lava of rhyolitic composition. A significant mafic eruptive event occurred about 7,000 years ago along the northwest rift zone. This event produced lavas ranging in composition from basalt to andesite, which erupted over a distance of 35 km from south of the caldera to Lava Butte where erupted lava flowed west to temporarily block the Deschutes River. Because of Newberry Volcanos proximity to populated areas, the presence of hot springs within the caldera, and the long and recent history of eruptive activity (including explosive activity), the U.S. Geological Survey installed monitoring equipment on the volcano. A recent geophysical study indicates the presence of magma at 3 to 5 km beneath the caldera.

The writing of this guide was prompted by a field trip to Crater Lake and Newberry Volcano organized in conjunction with the August 2017 IAVCEI quadrennial meeting in Portland, Oregon. Both field trip guides are available online. These two volcanoes were grouped in a single field trip because they are two of the few Cascades volcanoes that have generated calderas and significant related tephra deposits.

Suggested Citation

Jensen, R.A., and Donnelly-Nolan, J.M., 2017, Field-trip guide to the geologic highlights of Newberry Volcano, Oregon: U.S. Geological Survey Scientific Investigations Report 2017–5022–J2, 30 p., https://doi.org/10.3133/sir20175022J2.

ISSN: 2328-0328 (online)

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Table of Contents

  • Preface
  • Contributing Authors
  • Introduction
  • A Short History of Geologic Work at Newberry Volcano
  • Some Useful References
  • Logistics
  • About the Units Used in This Guide
  • Road Log
  • References Cited

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Field-trip guide to the geologic highlights of Newberry Volcano, Oregon
Series title Scientific Investigations Report
Series number 2017-5022
Chapter J2
DOI 10.3133/sir20175022J2
Year Published 2017
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Volcano Science Center
Description viii, 30 p.
Country United States
State Oregon
Other Geospatial Newberry Volcano
Online Only (Y/N) Y