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Geology and History Summary for Newberry Volcano

Rising gradually southward to 4,000 feet above the City of Bend, Oregon, Newberry Volcano appears from Bend as a broad ridge on the horizon. The volcano lies east of the Cascade Range crest at the western margin of a broad volcanic region known as the High Lava Plains. Extending approximately 115 km (75 mi) north to south and 45 km (27 mi) east to west, the volcano and its extensive apron of lava flows cover almost 3,200 km2 (1,200 mi2), an area about the size of the State of Rhode Island, making it the most aerally extensive volcano of the Cascades volcanic chain. Newberry lava flows underlie downtown Bend and the Redmond Municipal Airport.

This giant volcano is unlike a typical Cascade Range cone-shaped volcano (called a “stratocone”), such as South Sister to the west of Bend or Mount Rainier in Washington State. Instead, Newberry is a shield-shaped volcano formed by the full range of lava types (basalt to rhyolite) that erupted in diverse styles, and it has as many as 400 volcanic vents scattered across its slopes. Vents, such as cinder and spatter cones, are commonly aligned north-northwest to south-southeasteast, reflecting a strong regional tectonic influence.

Growth of the broad Newberry shield began about 400,000 years ago and styles of activity have ranged from explosive eruptions that produced ash to vast lava flows. Very explosive eruptions, similar to that of Mount St. Helens in 1980, have occurred near Newberry’s summit and produced high plumes and flows of hot volcanic gases and ash (jagged tiny particles of rock and volcanic glass). A much bigger explosive eruption produced the large volcanic depression or “caldera” at the summit; its associated volcanic-ash deposits can be found as far away as the San Francisco Bay Area in California. Between the end of the last Ice Age (about 12,000 years ago) and 7,700 years ago, Newberry Volcano erupted at least a dozen times. It is certain to erupt again, and if signs of volcanic unrest are detected, the USGS will issue advisories on the likely course of events.