(MT) – Between Sept. 29 and Oct. 2, the United States Geological Survey
(USGS) Cascades Volcano Observatory (CVO), in cooperation with the U.S.
Forest Service and Mount Hood National Forest, installed three new volcano
monitoring stations on the flanks of Mount Hood. The three stations enhance
the existing seismic, GPS and volcanic gas monitoring network that is
currently in operation around Mount Hood.

Each station includes seismic and GPS instruments, including a broadband
seismometer that detects the tiny earthquakes, smaller than Magnitude (M)
1.0 and not felt by humans, caused when magma, gas or fluids move beneath
the volcano. The GPS equipment measures subtle ground deformation of the
volcano in response to magma entering or leaving the magma reservoir
several miles below the summit.

Mount Hood has erupted repeatedly for hundreds of thousands of years, but
its most recent eruption series was from 1781 to 1793, just before the arrival
of Lewis and Clark in 1805. While Mount Hood is not currently erupting, it
produces frequent earthquakes and earthquake swarms, and steam and
volcanic gases are emitted in the area around Crater Rock near the volcano’s
summit.

Because of the significant hazards the volcano poses to nearby communities
and infrastructure as well as to aviation, USGS researchers designated Mount
Hood as a very high threat volcano in an updated 2018 National Volcanic
Threat Assessment. Factors in this included its proximity to nearby
communities and popular recreation areas, major highways and potential to
impact airspace affecting the Portland metropolitan area during unrest or
eruption.

Data from these unoccupied, remote monitoring stations are transmitted in
real-time data to the Cascades Volcano Observatory and its monitoring
partner, the Pacific Northwest Seismic Network (PNSN). View data from these

new stations on the CVO webpage, https://www.usgs.gov/volcanoes/mount-
hood/monitoring (all monitoring data streams), or at
https://pnsn.org/volcanoes/mount-hood (earthquakes only).

Mount Hood seismicity is monitored by the PNSN and CVO via a regional
network that includes five seismic stations within 12 miles of the volcano.
Robust monitoring networks are a key tool for mitigating volcano hazards that
will affect people and property. Volcanoes can awaken rapidly — in just days
to weeks — and initial precursors to that awakening can be subtle, including
small earthquakes, small ground movements and minor changes in gas
chemistry.

The most effective volcano monitoring network requires that instruments be
installed in multiple locations on the volcano’s flanks well before unrest begins
to catch these early changes.

Mount Hood is one of the most seismically active volcanoes in the Washington
and Oregon Cascades, and the most seismically active volcano in Oregon. In
an average month, up to two earthquakes are located by the Pacific Northwest
Seismic Network (PNSN) within three miles of the summit.

Most Hood earthquakes don't actually occur directly beneath the volcano's
summit, but instead in one of several clusters located two to three kilometers
to the west, southwest and southeast of the summit.

The largest earthquake recorded in the vicinity of Mount Hood was a M 4.5 in
2002 that was widely felt and followed by a M 3.8 aftershock four hours later.
Seismic events greater than M 3.0 also occurred in 1989, 1990, 1996 and
2010. Earthquakes in these clusters tend to occur in swarms (defined as three
or more located earthquakes in a single day) or "mainshock- aftershock"
sequences.

Scientists believe that earthquakes in the clusters south of the summit occur
on tectonic faults and aren't directly related to volcanic processes occurring
beneath Mount Hood. The largest earthquake recorded beneath the summit
was a M 3.5 in 1989 that was felt. In contrast to the southerly clusters,
earthquakes directly beneath the summit rarely occur in swarms.