Volcanic monitoring stations installed on Mount Hood posted on 01/01/2021
(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.
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