USGS/Cascades Volcano Observatory, Vancouver, Washington
DESCRIPTION:
Oregon Volcanoes and Volcanics
- Cascade Range
- Central Oregon High Cascades
- Coast Range
- Willamette Valley
- Oregon Volcanoes
From:
Wood and Kienle, 1990, Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p., p.149,
Contribution by Charles A. Wood.
-
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.
-
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.
-
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. ...
-
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. ...
-
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.
-
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 Volcanoes and Volcanics Menu
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Cascade Range Earthquakes and Seismicity Menu
Central Oregon High Cascades
|
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Central Oregon High Cascades Menu
From:
Gannett and Caldwell,
Geologic Framework of the Willamette Lowland Aquifer System, Oregon and
Washington: USGS Professional Paper 1424-A.
-
The Coast Range, to the west of the Willamette lowland,
consists of several thousand feet of Tertiary marine sandstone,
siltstone, shale, and associated volcanic and
intrusive rocks.
From:
Gannett and Caldwell,
Geologic Framework of the Willamette Lowland Aquifer System, Oregon and
Washington: USGS Professional Paper 1424-A.
-
The Willamette Lowland is a structural and erosional
lowland between uplifted marine rocks of the Coast Range
and volcanic rocks of the
Cascade Range.
The Willamette Lowland study area
encompasses approximately 5,680 square miles,
3,700 square miles of which
are underlain by basin-fill deposits.
The Coast Range, to the west of the lowland,
consists of several thousand feet of Tertiary marine
sandstone, siltstone, shale, and associated
volcanic and intrusive rocks. The Cascade Range,
to the east of the lowland, consists of
volcanic lava flows, ash-flow tuffs,
and pyroclastic and epiclastic debris.
Continental and marine strata interfinger beneath and adjacent
to the Willamette Lowland. In the northern
two-thirds of the lowland, the marine
sedimentary rocks and Cascade Range volcanic rocks
are overlain by up to a thousand feet of
lava of the
Columbia River Basalt Group.
Folding and faulting during and after incursion of the
Columbia River Basalt Group formed four
major depositional basins. These basins,
separated in most places by uplands capped by the
Columbia River Basalt Group, have locally
accumulated more than 1,600 feet of fluvial
sediment derived from the Cascade and Coast
Ranges or transported into the region by the
Columbia River. During Pleistocene time,
large-volume glacial-outburst floods, which
originated in western Montana, periodically
flowed down the Columbia River drainage and
inundated the Willamette Lowland. These
floods deposited up to 250 feet of silt,
sand, and gravel in the Portland Basin, and
up to 130 feet of silt, known as the Willamette Silt,
elsewhere in the Willamette Lowland.
Giver, R.W., and Wells, R.E., 2001,
Shaded-Relief and Color Shaded-Relief Maps of the
Willamette Valley, Oregon: U.S.
Geological Survey Open-File Report 01-294.
-
Most of Oregon's population, technology and agricultural
centers, and important transportation, power, and
communications lifelines are located in the Willamette
Valley of western Oregon. The lowlands of the Willamette
Valley extend about 120 km along the Willamette River and
contain the major cities of Portland, Salem, Corvallis, and
Eugene. The valley is subject to a variety of earthquake
hazards (Madin, 1990), and its water and geologic
resources are under pressure from rapid urbanization
(Gannett and Caldwell, 1998).
-
The valley is part of the Willamette River drainage
basin, which covers 31,715 km 2 between the crest of the
Oregon Coast Range on the west and the Cascade Range to
the east (Gannett and Caldwell, 1998). The Willamette
River is the largest river in the valley and is fed by several
major tributaries, including the McKenzie, Calapooia,
Santiam, Tualatin, Yamhill and Clackamas Rivers. The
valley is the major source of ground and surface water for
the population centers.
-
The valley consists of four sub-basins: the southern
and northern Willamette basins, the Tualatin basin, and the
Portland basin (see Figure 1). The Waldo Hills separate the
southern Willamette basin from the northern basin, and the
Chehalem Mountains separate the northern basin from the
Tualatin Basin. Northeast of the Tualatin basin, the Tualatin
Mountains form the divide with the Portland Basin.
-
The Willamette Valley lies within a fore-arc basin
between the Cascade Volcanic Arc and the Coast Ranges
that may have originated in early Tertiary time (Yeats and
others, 1996). Some of the sub-basins have accumulated
several hundred meters of sediment in late Cenozoic time.
The northern basins also contain lavas of the Miocene
Columbia River Basalt Group (CRBG). Flows of the
CRBG entered the valley approximately 16 million years
ago through a low in the Cascade Range and spread into the
Portland and northern Willamette basins. The Tualatin
Mountains, Chehalem Mountains, Waldo Hills, and Salem
Hills are largely composed of CRBG flows that dip inward
toward the basin centers (Beeson, and others, 1989, Yeats,
and others, 1996). Approximately 3.0 to 0.26 Ma, the
Boring Lavas were erupted from several vents throughout
the northern Willamette, Portland, and Tualatin basins
(Conrey and other, 1996, Madin, 1990, Madin, 1994).
Boring Lavas capped the Oregon City plateau (Yeats, and
others, 1996) and created many of the prominent small
cone-shaped hills and mountains southeast of downtown
Portland (Madin, 1990). Between 15,000 and 12,700 years
ago catastrophic floods from glacial Lake Missoula
inundated the majority of the Willamette Valley (O'Connor
and others, 2001). These floods reached up to 120 meters
above sea level covering the valley with up to 35 meters of
sediment and depositing ice-rafted boulders foreign to the
Willamette Valley as far south as Eugene, Oregon (Allison,
1935, Waitt, 1980, O'Connor and Others, 2001).
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America's Volcanic Past - Oregon
-- Volcanic Highlights and Features
From:
"Catalog of Active Volcanoes of the World" (CAVW),
Smithsonian Institution, Global Volcanism Program Website, 2002
- Volcano Name, Latitude, Longitude, Elevation, Volcano Type, and Type of
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Bachelor, 43.979 N, 121.688 W, 2763 meters,
Stratovolcano, Tephrochronology
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Belknap, 44.285 N, 121.841 W, 2095 meters,
Shield volcanoes, Radiocarbon
- Blue Lake Crater, 44.42 N, 121.77 W, 1230 meters,
Maar, Radiocarbon
- Cinnamon Butte, 43.241 N, 122.108 W, 1956 meters,
Cinder cones, Holocene?
-
Crater Lake, 42.93 N, 122.12 W, 2487 meters,
Caldera, Radiocarbon
- Davis Lake, 43.57 N, 121.82 W, 2163 meters,
Volcanic field, Radiocarbon
- Devils Garden, 43.512 N, 120.861 W, 1698 meters,
Volcanic field, Holocene?
- Diamond Craters, 43.10 N, 118.75 W, 1435 meters,
Volcanic field, Holocene?
- Four Craters Lava Field, 43.361 N, 120.669 W, 1501 meters,
Volcanic field, Holocene?
-
Hood, 45.374 N, 121.694 W, 3426 meters,
Stratovolcano, Historical
- Imagination Peak, 42.552 N, 122.201 W, 1986 meters, Pyroclastic cone, Holocene?
- Jackies Butte, 42.606 N, 117.589 W, 1420 meters,
Volcanic field, Holocene?
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Jefferson, 44.692 N, 121.80 W, 3199 meters,
Stratovolcano, Varve Count
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Jordan Craters, 43.03 N, 117.42 W, 1473 meters,
Volcanic field, Holocene
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Newberry Volcano, 43.722 N, 121.229 W, 2434 meters,
Shield volcano, Radiocarbon
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North Sister Field, 44.17 N, 121.77 W, 3074 meters, Complex volcano, Radiocarbon
- Saddle Butte, 43.00 N, 117.80 W, 1700 meters,
Volcanic field, Holocene?
- Sand Mountain Field, 44.38 N, 121.93 W, 1664 meters,
Cinder cones, Radiocarbon
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South Sister, 44.10 N, 121.77 W, 3157 meters, Complex volcano, Radiocarbon
- Squaw Ridge Field, 43.472 N, 120.754 W, 1711 meters,
Volcanic field, Holocene?
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Washington (Mount Washington), 44.332 N, 121.837 W, 2376 meters,
Shield volcano, Radiocarbon
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12/01/03, Lyn Topinka