Rewriting the recent history of productive Cascade Arc volcanoes

Date:
August 14, 2020
Source:
University of Oregon
Summary:
Volcanic eruptions in the Cascade Range of the Pacific Northwest
over the last 2.6 million years are more numerous and closely
connected to subsurface signatures of currently active magma than
commonly thought, according to newly publish research.



FULL STORY ========================================================================== Volcanic eruptions in the Cascade Range of the Pacific Northwest over
the last 2.6 million years are more numerous and closely connected to subsurface signatures of currently active magma than commonly thought, according to newly published research.


==========================================================================
A synthesis of volcanic vents on the surface and data that probes the
structure and composition of the crust to a depth of 20 kilometers (12.4
miles) makes clear new connections between surface and subsurface evidence
of past volcanic eruptions. The activity has stretched far beyond the
11 well known stratovolcanoes lining the Cascade Arc between northern California and northern Washington.

The study, led by University of Oregon scientists, catalogued almost
3,000 volcanoes associated with the mountain range. It was published
July 13 in the journal Geology.

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

"Anyone who has ever flown between San Francisco and Seattle has probably 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 volcanoes in
the Cascades that have erupted in the geologically recent past."
The three-member research team examined 2,835 vents. They used freely
available satellite-derived 3D digital terrain models to update estimates
of eruption rates and synthesize subsurface observations over recent
decades to map where signs of active magma in the crust correlates with edifices on the surfaces around the region's volcanos.



========================================================================== Edifices refer to the main portion of volcanoes built by erupted lava,
rock projectiles, mud and debris flows, and mixture of rock fragments,
gas and ash.

The 3D models allowed the research team to associate volcanic edifices
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 vents seem to overlay 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 volcano 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 edifices represent about 50 percent of total volcanic
output during the time-period we examined." The research, he added,
indicated a systematic decrease in the strength of these relationships, suggesting that eruptions as well as their underlying plumbing systems
have migrated during the past 2.6 million years.

The National Science Foundation-funded research can help guide more
in-depth studies of distributed volcanic vents and in assessing hazards
and risks to people and infrastructure, said co-author David W. Ramsey
of the U.S.

Geological Survey's Cascades Volcano Observatory in Vancouver, Washington.

Distributed volcanic vents are associated with small cinder cones that
cover much of the central Oregon Cascades, and area 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 U.S. Cascade Range over the last 2.6 million years,"
Ramsay said.

"It helps to 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 the snow-capped stratovolcanoes on the horizon." The region's major 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.


========================================================================== Story Source: Materials provided by University_of_Oregon. Original
written by Jim Barlow.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. David W. Ramsey, Leif Karlstrom, Daniel O'Hara. Time-evolving
surface and
subsurface signatures of Quaternary volcanism in the Cascades arc.

Geology, 2020; DOI: 10.1130/G47706.1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200814142937.htm

--- up 4 weeks, 2 days, 1 hour, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)