USGS/Cascades Volcano Observatory, Vancouver, Washington
DESCRIPTION:
Washington State Volcanoes and Volcanics
- Washington State's Major Volcanoes
- Cascade Range
- Earthquakes and Seismicity
- Washington State Volcanoes
- Washington State Volcanic Highlights and Features
Washington State's Major Volcanoes
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["Pictogram",356K,InlineGIF]
Major Washington State Volcanoes
From:
Pringle, P.T., and Scott, K.M., 2001,
Postglacial Influence of Volcanism on the Landscape and
Environmental History of the Puget Lowland, Washington:
A Review of Geologic Literature and Recent Discoveries, with
Emphasis on the Landscape Disturbances Associated with
Lahars, Lahar Runouts, and Associated Flooding:
Fifth Puget Sound Research Conference, February 12-14, 2001,
Puget Sound Research 2001 and Washington Department of Natural Resources Website, 2002
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Washington is home to five major
composite volcanoes or stratovolcanoes:
Mount Baker,
Glacier Peak,
Mount Rainier,
Mount St. Helens, and
Mount Adams.
These volcanoes and nearby
Mount Hood
are part of
the
Cascade Range,
a volcanic arc that stretches
from southwestern British Columbia to Northern
California. Although there are thousands of
small basaltic or basaltic-andesite volcanoes in the Cascade
Range, the 13 major composite volcanic centers
in the U.S. part of the range have been the focus of most
hazards concerns and studies. During the past 12,000 years,
these volcanoes have produced more than 200
eruptions that have generated tephra (ejected material),
lava flows, and lahars, and debris avalanches
(Miller 1990). Earthquakes, intrusions of magma,
or steam explosions may have caused some enormous
debris avalanches and lahars whose deposits
apparently do not correlate with major tephra layers.
All Washington volcanoes except for Mount Adams have
erupted since the birth of the United States in
1776, and all of them, as well as Mount Hood,
have active seismicity and/or geothermal activity.
Scott (1990) provides a compilation of eruptive histories
and hazards from major Cascade peaks in Washington
and Oregon.
From:
Wood and Kienle, 1990, Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p., p.149,
Contribution by Charles A. Wood.
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Holocene volcanism in the Cascades extends from the
Garibaldi Volcanic Belt in southern British Columbia
to the
Lassen volcanic complex in northern California.
Pronounced differences in the nature of volcanism occur along the arc. In
Washington there are five, generally large, widely spaced
stratovolcanoes,
with only one
(
Mount Adams)
having significant nearly basaltic volcanics. In marked contrast, Oregon
has six generally smaller stratovolcanoes, but the entire state is traversed by
a 40-50-kilometer-wide band of basaltic to andesitic
lava shields,
cinder cones,
and smaller stratovolcanoes that the "Cascade" cones rise above. South of
Crater Lake,
the Cascade arc bends perceptibly toward the southeast, and continues
along this trend to
Lassen Peak.
Both Lassen and
Shasta
are associated with eastward halos of mafic shields and lava fields which, near
Shasta, culminate in the huge shield volcano of
Medicine Lake.
From:
Swanson, et.al., 1989,
Cenozoic Volcanism in the Cascade Range and Columbia Plateau,
Southern Washington and Northernmost Oregon:
AGU Field Trip Guidebook T106.
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The Cascade Range has been an active arc for about 36 million years as a
result of
plate convergence.
Volcanic rocks between 55 and 42 million years ago occur in the Cascades, but
are probably related to a rather diffuse volcanic episode that created the
Challis arc extending southeastward from northern to northwest Wyoming.
Convergence between the North American and
Juan de Fuca plates
continues at
about 4 centimeters per year in the direction of North-50-degrees-East, a
slowing of 2-3 centimeters per year since 7 million years ago. According to
most interpretations, volcanism in the Cascades has been discontinuous in time
and space, with the most recent episode of activity beginning about 5 million
years ago and resulting in more than 3000 vents.
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In Oregon, the young terrane is commonly called the
High Cascades
and the old terrane the Western Cascades,
terms that reflect present physiography and geography.
The terms are not useful in Washington, where young
vents are scattered across the dominantly middle Miocene and older terrane. ...
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In
Washington
and Oregon,
a striking contrast has existed for the past 5 million
years in the style of volcanism in the Cascades relative to geography. North of
Mount Rainier,
young volcanism is concentrated in only a few isolated andesitic and dacitic
composite cones
(notably
Glacier Peak,
Mount Baker, and the volcanoes of the
Garibaldi belt in British Columbia),
whereas south of
Mount Hood
moderate-sized andesitic and dacitic composite cones are
relatively unimportant features of a landscape dominated by small andesite and
basalt vents. The area between Mounts Rainier and
Hood is transitional; large
andesite and dacite composite cones
(
Rainier,
Adams,
St. Helens,
Hood,
and the extinct
Goat Rocks volcano)
occur together with fields and scattered vents of olivine basalt
(
Indian Heaven,
Simcoe Mountains,
and the
King Mountain fissure zone south of Mount Adams. ...
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Cascade Range Volcanoes and Volcanics Menu
Earthquakes and Seismicity
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From:
Washington State Department of Natural Resources, Division of Geology and Earth Resources
Website, 2002
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Washington is situated
at a convergent continental margin,
the collisional boundary between two tectonic plates.
The Cascadia subduction zone, which is the
convergent boundary between the North America plate and the Juan de Fuca
plate, lies offshore from northernmost California
to southernmost British Columbia. The two plates are converging at a rate
of about 3-4 centimeters per year (about 2 inches per year);
in addition, the northward-moving Pacific plate is pushing the
Juan de Fuca plate
north, causing complex seismic strain to accumulate.
Earthquakes are caused by the abrupt release of
this slowly accumulated strain.
From:
Swanson, et.al., 1989,
Cenozoic Volcanism in the Cascade Range and Columbia Plateau,
Southern Washington and Northernmost Oregon:
AGU Field Trip Guidebook T106.
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The southern Washington Cascades are seismically active. Most earthquakes occur
along the 100-kilometer-long, north-northwest trending St. Helens seismic zone,
where most focal mechanisms show dextral slip parallel to the trend of the zone
and consistent with the direction of plate convergence. Other crustal
earthquakes concentrate just west of Mount Rainier and in the Portland
(Oregon) area. Few earthquakes occur north of
Mount Rainier or south of Mount Hood.
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From tomography, Rasmussen and Humphreys (1988) interpret the subducted
Juan de Fuca plate
as a quasi-planar feature dipping about 65 degrees to about 300 kilometers under
the southern Washington Cascades. The plate is poorly defined seismically,
however, owing to a lack of earthquakes within it. Guffanti and Weaver
(1988) show that the present volcanic front of the Washington Cascades, defined
by the westernmost young vents, parallels the curved trend of the subducting
plate reflected by the 60 kilometer-depth contour. The front trends northwest in
northern Washington -- where Glacier Peak, Mount Baker, and the
volcanoes of southern British Columbia occur along a virtually straight line --
and northeast in southern Washington. A 90-kilometer gap free of young
volcanoes between Mount Rainier and Glacier Peak is landward of
that part of the subducting plate with the least average dip to a depth of 60
kilometers. South of
Portland,
the volcanic front is offset 50 kilometers
eastward and extends southward into California, probably still parallel to the
trend of the convergent margin.
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Cascade Range Earthquakes and Seismicity Menu
Washington State Volcanoes
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From:
"Catalog of Active Volcanoes of the World" (CAVW),
Smithsonian Institution, Global Volcanism Program Website, 2002
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Volcano Name; Latitude; Longitude; Elevation; Volcano Type; and Type of
evidence for Holocene activity
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Adams; 46.206 N, 121.490 W; 3,742 meters;
Stratovolcano; Tephrochronology
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Baker; 48.786 N, 121.82 W; 3,285 meters;
Stratovolcano; Historical
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Glacier Peak; 48.112 N, 121.113 W; 3,213 meters;
Stratovolcano; Tephrochronology
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Indian Heaven; 45.93 N, 121.82 W; 1,513 meters;
Shield volcanoes; Radiocarbon
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Rainier; 46.87 N, 121.758 W; 4,392 meters;
Stratovolcano; Dendrochronology
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St. Helens; 46.20 N, 122.18 W; 2,549 meters;
Stratovolcano; Historical
- West Crater; 45.88 N, 122.08 W; 1,329 meters;
Volcanic field; Radiocarbon
From:
Wood and Kienle, 1990,
Volcanoes of North America: United States and Canada:
Cambridge University Press, variety of contributors
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Volcano or Feature Name; Location; Elevation; Volcano Type; Composition
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Adams; 46.2 N, 121.5 W; 3,742 meters;
Compound stratovolcano with approximately 60 peripheral vents;
Andesite, basalt, dacite to rhyodacite
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Ape Cave;
south of
Mount St. Helens; elevation not given, 3.4 kilometers long;
Longest known uncollapsed segment of a
Lava Tube
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Baker; 48.79 N, 121.82 W; 3,285 meters;
Stratovolcano; Andesite with minor basalt
- Bare Mountain;
south of
Mount St. Helens; 1,329 meters;
Tertiary intrusive andesite
- Berry Mountain;
Indian Heaven Volcanic Field; 1,523 meters;
Shield Volcano
- Bird Mountain;
Indian Heaven Volcanic Field; 1,739 meters;
Shield Volcano
- Columbia Crest;
250-meter-high summit cone of
Mount Rainier
- Crazy Hills;
Indian Heaven Volcanic Field; elevation not given;
Moberg
- East Crater;
Indian Heaven Volcanic Field; 1,614 meters;
Shield Volcano
- East Dome;
on east base of
Mount St. Helens; elevation not given;
Volcanic Dome; Rhyodacitic composition
- Echo Rock;
satellitic cone on northwest flank of
Mount Rainier
- Gifford Peak;
Indian Heaven Volcanic Field; 1,636 meters;
Shield Volcano
- Gilbert Peak;
Goat Rocks Volcanic Field; 2,494 meters;
Highest point of Goat Rocks Volcanic Field, capped with lava flow of hornblende andesite
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Glacier Peak; 48.12 N, 121.113 W; 3,213 meters;
Dacite dome cluster; Andesite to dacite
- Goat Rocks Dome;
on northwest flank of
Mount St. Helens; 600-700 meters below pre-1980 summit;
Volcanic Dome
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Goat Rocks Volcanic Center; 46.50 N, 121.45 W; 1,340 to 2,494 meters;
Stratovolcano;
High-K2O pyroxene and minor hornblende andesite
- Hogback Mountain;
south of White Pass; 700 meters;
Shield Volcano
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Indian Heaven; 46.00 N, 121.75 W; 720 to 1,806 meters;
Polygenetic volcanic field;
Olivine tholeiite, calc-alkaline basalt and andesite
- Lemei Rock;
Indian Heaven Volcanic Field; 1,806 meters;
Shield Volcano
- Lincoln Plateau; east of
Mount Adams; elevations not given;
Shield volcano and lava flows
- Lone Butte;
Indian Heaven Volcanic Field; elevation not given;
Tuya
- Marble Mountain - Trout Creek Hill Zone; 45.9 N, 122.0 W; 150 to 1,378 meters;
Series of cones and shields; Mostly calc-alkaline, medium-K basalt and andesites
- Marble Mountain; south of
Mount St. Helens; 1,255 meters;
Shield Volcano
- Observation Rock;
satellitic cone on northwest flank of
Mount Rainier
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Rainier; 46.85 N, 121.75 W; 4,392 meters;
Stratovolcano;
Basaltic andesite to andesite
- Red Mountain;
Indian Heaven Volcanic Field; 1,513 meters;
Shield Volcano
- Sawtooth Mountain;
Indian Heaven Volcanic Field; 1,632 meters;
Shield Volcano
- Schreibers Meadow;
satellitic cone on
Mount Baker;
elevation not given;
760-meter-wide and 100-meters-high
Cinder Cone and 11-kilometer-long lava flow
- Sherman Crater;
450-meter-wide vent on
Mount Baker's summit
- Signal Peak;
Simcoe Mountains Volcanic Field; elevation not given; dacite composition
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Simcoe; 46.1 N, 120.9 W; elevations not given;
Monogenetic volcano field;
Olivine basalt, andesite, and rhyolite
- Sugar Bowl;
on north flank of
Mount St. Helens just east of the mouth of the present crater; elevation not given;
Volcanic Dome; Rhyodacitic composition
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St. Helens, 46.20 N, 122.19 W, 1,000 to 2,500 meters (2,950 before 18 May, 1980),
Stratovolcano, Basalt to rhyodacite, chiefly andesite and dacite
- West Crater;
south of
Mount St. Helens; 1,282 meters;
Andesitic
dome with two large adjacent lava flows
Washington State Volcanic Highlights and Features
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America's Volcanic Past - Washington State
-- Volcanic Highlights and Features
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03/14/02, Lyn Topinka