Oregon sits within the Cascade Volcanic Arc, which forms a segment of the Pacific Ocean’s “Ring of Fire.” This geological setting is created by the subduction of the Juan de Fuca tectonic plate beneath the North American plate, generating the magma that feeds the region’s volcanoes. The state’s landscape features a wide variety of volcanic features, ranging from classic snow-capped peaks to massive shield volcanoes and dramatic calderas. This diverse collection of vents and mountains has shaped the geography of the state.
Oregon’s Iconic Cascade Peaks
The Cascade Range features towering stratovolcanoes, which form steep, symmetrical cones built from alternating layers of lava flows and ash. Rising to 11,244 feet, Mount Hood is the state’s highest point and an andesite-dacite stratovolcano located near Portland. Its eruptive history involves the gradual growth and collapse of lava domes, which generate hazardous volcanic mudflows called lahars. The most recent major eruptive period occurred in the 1780s, leaving behind a 550-foot-high lava dome at Crater Rock.
South of Mount Hood is Mount Jefferson, Oregon’s second tallest peak at 10,495 feet. This stratovolcano has an older record of activity; its main cone has not erupted in the last 10,000 years. Further south, the Three Sisters complex consists of North, Middle, and South Sister, all rising above 10,000 feet. South Sister is the most recently active of the three, with a rhyolitic eruption occurring around 2,000 years ago.
Diverse Volcanic Landscapes
Crater Lake is a caldera created by the collapse of Mount Mazama, once a 12,000-foot stratovolcano. This occurred 7,700 years ago when an explosive eruption emptied the underlying magma chamber. The summit fell inward, forming a caldera five by six miles wide.
Newberry Volcano, located east of the main Cascade crest near Bend, is a massive volcanic structure. It is a broad, shield-shaped composite volcano built from half a million years of eruptions, covering an area roughly the size of Rhode Island. The volcano’s summit holds an eight-by-six-kilometer caldera, formed about 75,000 years ago, which now contains Paulina and East Lakes. Newberry’s most recent eruption, about 1,300 years ago, created the Big Obsidian Flow, one of the youngest lava features in Oregon.
Hundreds of cinder cones and monogenetic vents are scattered across the state, particularly near Newberry and the Three Sisters. These features, along with lava fields, demonstrate the wide range of magma compositions and eruptive styles present in the Cascades.
Current Status and Monitoring Efforts
All major volcanic centers in Oregon are considered potentially active, meaning they are likely to erupt again. Currently, all monitored Cascade volcanoes are at normal background activity levels, indicating no immediate threat. The U.S. Geological Survey (USGS) and the Cascades Volcano Observatory (CVO) in Vancouver, Washington, are responsible for continuously monitoring these systems.
Monitoring relies on dense networks of ground-based sensors designed to detect subtle changes. Seismometers track small earthquakes that indicate magma movement. GPS receivers and tiltmeters measure ground deformation, such as swelling or uplift, signaling pressure beneath the surface. Volcanic gas detection equipment analyzes changes in the composition or output of gases like sulfur dioxide from fumaroles. These expanded monitoring networks ensure scientists can provide timely warnings of volcanic unrest.