Study rewrites recent history of productive Arc Cascade volcanoes

Volcanic eruptions in the Pacific Northwest Cascade Range over the 2.6 million years are more numerous and closely related to the subsurface signatures of currently active magma than is generally believed, according to recently published research .

A synthesis of volcanic vents at the surface and data that probes the structure and composition of the crust to a depth of 20 kilometers (12.4 miles) establishes new, clear connections between the surface and the subsoil evidence of past volcanic eruptions. Activity has spread far beyond the 11 well-known stratovolcanoes bordering the Arc des Cascades between northern California and northern Washington.

The study, led by scientists at the University of Oregon, identified nearly 3,000 volcanoes associated with the mountain range. It was published on July 13 in the newspaper Geology.

The research reveals new details about the complex and evolutionary patterns of magma rise in the region, said study co-author Leif Karlstrom, professor in the UO Department of Earth Sciences and the Center for volcanology of Oregon.

“Anyone who has ever flown between San Francisco and Seattle has likely marveled at the massive stratovolcanoes lined up between northern California and southern British Columbia,” he said. “Remarkably, these landforms represent less than 1 percent of the Cascade volcanoes that erupted in the geologically recent past.”

The three-member research team examined 2,835 vents. They used 3D digital terrain models derived from freely available satellites to update estimates of eruption rates and synthesize subsurface observations over the past decades to map where signs of active magma in the crust correlate with buildings on surfaces around volcanoes in the region.

The edifices refer to the main part of volcanoes built by eruptions of lava, rock projectiles, mudslides and debris, and a mixture of fragments of rock, gas and ash.

The 3-D models allowed the research team to associate the volcanic edifices with the 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 vents appear to cover the currently active magma transport structures in the crust.

“Previous studies have analyzed single volcanoes or volcanic clusters with satellite data, but this is the first study to constrain the geometries of volcanoes over an entire arc in a coherent manner,” said lead author of the study, Daniel O’Hara, doctoral student at UO. student. “We estimate that volcanic edifices account for about 50 percent of total volcanic production during the period we have examined.”

Research, he added, indicated a systematic decrease in the strength of these relationships, suggesting that the eruptions along with their underlying plumbing systems migrated over the 2.6 million years.

Research funded by the National Science Foundation can help guide more in-depth studies of distributed volcanic vents and assess hazards and risks to people and infrastructure, observatory co-author David W. Ramsey said. of the US Geological Survey’s Cascade Volcanoes in Vancouver, Washington. .

The distributed volcanic vents are associated with small cones of ash that cover much of central Oregon’s waterfalls, and areas such as the boring lava field in the city of Portland and the Medicine Lake volcano in California.

“This research used a consistent methodology to analyze volcanic vents spanning the entire United States Cascade Range over 2.6 million years,” Ramsay said. “This helps highlight recently active volcanic vents, particularly in central Oregon and northern California, and shows that the locations of potential future eruptions are not limited to snow-capped stratovolcanoes on the horizon. “

The main stratovolcanoes in the region extend along the junction of the Juan de Fuca and North American plates. From north to south, these are the Baker Mountains, Glacier Peak, Mount Rainier, Mount St. Helens, Mount Adams, Mount Hood, Mount Jefferson, Three Sisters, Crater Lake / Mount Mazama, Mount Shasta and Lassen Peak.