Study recounts the recent history of productive Cascade Arc volcanoes

Volcanic eruptions in the Cascade Range of the Pacific Northwest over the past 2.6 million years are multiple and closely related to signatures on the surface of currently active magma than normally thought, according to newly published research.

A synthesis of volcanic valves on the surface and data examining the structure and composition of the crust to a depth of 20 kilometers (12.4 miles) make new connections between surface and subsurface evidence of volcanic eruptions in the past. The activity extends far beyond the 11 known stratovolcanoes that line the Cascade Arc between northern California and northern Washington.

The study, led by scientists from the University of Oregon, cataloged nearly 3,000 volcanoes associated with the mountain range. It was published July 13 in the magazine Geology.

The study reveals new details about the complex and time-evolving patterns of rising magma in the region, said student-author Leif Karlstrom, a professor in the UO department of Earth Sciences and Oregon Center for Volcanology.

“Anyone who has ever fled between San Francisco and Seattle has marveled at the massive stratovolcano that is erupting between northern California and southern British Columbia,” he said. “Remarkably, these landforms represent less than 1 percent of the volcanoes in the Cascades that have formed in the geologically recent past.”

The three-member research team examined 2,835 valves. They used freely available satellite-derived 3-D digital terrain models to update estimates of eruption levels and map observations of the surface over the last decades to create signs where signs of active magma in the crust correlate with structures on ‘ the surfaces around the volcanoes of the region.

Buildings refer to the main body of volcanoes built by erupting lava, rock projectiles, mud and puddle currents, and a mix of rock fragments, gas and ash.

The 3-D models allowed the research team to associate volcanic buildings with underlying seismic velocities, heat flow, gravity and deformation that are sensitive to the presence of magma, Karlstrom said. The work, he added, showed where surface walls appear to be currently flooding active magma transport structures in the crust.

“Previous studies have analyzed single volcanoes as volcanic clusters using satellite data, but this is the first study to limit volcanic geometries over an entire arc in a self-consistent manner,” said the study’s lead author, Daniel O’Hara, a UO -doctoral student. “We estimate that volcanic buildings represent about 50 percent of the total volcanic output in the time period we examined.”

The study, he added, showed a systematic decline in the strength of these relationships, suggesting that eruptions, such as their underlying sanitary systems, have migrated over the past 2.6 million years.

The National Science Foundation’s funded study can help guide more in-depth studies of distributed volcanic valves and in assessing hazards and risks to humans and infrastructure, said co-author David W. Ramsey of the Cascades Volcano Observatory. of the U.S. Geological Survey in Vancouver, Washington.

Distributed volcanic valves are connected to small cinder cones that line much of central Oregon Cascades, and areas such as the Boring Lava Field in Portland and the Medicine Lake volcano in California.

“This research used a consistent methodology to analyze volcanic valves that span the entire U.S. Cascade Range over the past 2.6 million years,” Ramsay said. “It helps to mark recently active volcanic valves, particularly in central Oregon and northern California, and shows that the locations of possible future eruptions are not limited to the snow-capped stratovolcanoes on the horizon.”

The region’s most important stratovolcanoes stretch along the junction of the Juan de Fuca and North American plates. From north to south they are Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, Mount Adams, Mount Hood, Mount Jefferson, Three Sisters, Crater Lake / Mount Mazama, Mount Shasta and Lassen Peak.