USGS/Cascades Volcano Observatory, Vancouver, Washington
DESCRIPTION:
Cascade Range Volcanoes and Volcanics
- Cascade Range
- High Cascades and Western Cascades
- Plate Tectonics
- Volcanic Background
- Holocene Volcanism in the Cascades
- Earthquakes and Seismicity
- Cascade Range Volcanoes
- Mount Adams, Washington
- Mount Baker, Washington
- Crater Lake, Oregon
- Mount Garibaldi, British Columbia
- Glacier Peak
- Mount Hood, Oregon
- Mount Jefferson, Oregon
- Lassen Peak, California
- Meager Mountain, British Columbia
- Medicine Lake, California
- Newberry Caldera, Oregon
- Mount Rainier, Washington
- Mount Shasta, California
- Mount St. Helens, Washington
- Three Sisters, Oregon
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[Interactive Imagemap] ...
[Interactive Table] ...
From:
Hoblitt, Miller, and Scott, 1987,
Volcanic Hazards with Regard to Siting Nuclear-Power Plants
in the Pacific Northwest:
USGS Open-File Report 87-297
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... 13 volcanic centers
(1..
Mount Baker,
2..
Glacier Peak,
3..
Mount Rainier,
4..
Mount St. Helens,
5..
Mount Adams,
6..
Mount Hood,
7..
Mount Jefferson,
8..
Three Sisters,
9..
Newberry Caldera,
10..
Crater Lake (Mount Mazama),
11..
Medicine Lake,
12..
Mount Shasta,
13..
Lassen Peak) ...
are the most prominent volcanic features of
Quaternary age
in the Cascade Range ...
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.
High Cascades and Western Cascades
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From:
U.S. Forest Service Website, Deschutes and Ochoco National Forests,
2002
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The High Cascades province is characterized
by a north-trending belt of upper Miocene to
Quaternary volcanic rocks that were erupted
on the east margin of the upper Eocene to
Miocene Western Cascades province.
The late Pleistocene record of this volcanic activity is
well preserved on the crest of the High Cascades.
The best exposed record of the early Pleistocene,
Pliocene and late Miocene
Cascade volcanism is found in
volcanic and volcaniclastic deposits on
the east flank of the range and in the adjacent Deschutes Basin.
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Upper Pliocene and Quaternary rocks of the
High Cascades form a broad platform of
chiefly basalt and basaltic andesite volcanoes that
fill a structurally subsided zone in the
older rocks of the High Cascades.
Mount Hood,
Mount Jefferson,
Three Sisters-Broken Top,
and
Mount Mazama (Crater Lake)
are the four major
Quaternary volcanic centers along this platform.
These major volcanic centers have erupted
lava flows and pyroclastic material that ranges
in composition from basalt to dacite and with
the exception of Mount Hood have also erupted
rhyolite.
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Volcanism has continued until recent times
with the eruptions in the
Belknap Crater
area. The Belknap Crater area is a 19 miles long en
echelon zone of vents extending from the base of
the North Sister northward to the Santiam Pass.
The zone consists of the Belknap
shield volcano and numerous cinder cones and lava flows.
Eruptions have occurred between 4,000 and 1,500 years ago. Many of these
eruptions produced lava flows down the ancient
valley of the McKenzie River and Lost Creek which
dammed the rivers and formed lakes
and waterfalls.
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The Western Cascades province is
characterized as an older, deeply eroded
volcanic range lying west of the more recent snow-covered
High Cascade range. They range in elevation
from 1,700 feet on the western margin to 5,800 feet
on the eastern margin. The Western
Cascades began to form 40 million years
ago with eruptions from a chain of volcanoes
near the Eocene shoreline. Volcanic activity
gradually shifted to the east in the Miocene and Pliocene.
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The Western Cascades are made up almost
entirely of slightly deformed and partly
altered volcanic flows and pyroclastic rocks which
range in age from late Eocene to late Miocene.
These rocks have been heavily dissected by
erosion and the only evidence remaining of
the many volcanoes from which they were
erupted are occasional remnants of volcanic necks or
plugs which mark former vents. There
are also minor Pliocene to Pleistocene
intracanyon lavas derived from the
High Cascades or rare local vents.
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 3,000 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. ...
From:
Wood and Kienle, 1990, Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p., p.169,
Contribution by David R. Sherrod
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The
Cascade Range
in Oregon is customarily divided into two physiographic subprovinces;
Western Cascades and
High Cascades.
The High Cascades
subprovince is built of rocks mainly younger than 3.5 million
years and is the modern Cascade Range volcanic arc. In contrast, the
Western Cascades encompass a deeply eroded pile of chiefly Oligocene to
Pliocene volcanic and volcaniclastic rocks. ...
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The High Cascades in the areas south of Mount Jefferson to Santiam Pass
is a broad ridge built up by several
shield volcanoes
and numerous
cinder cones.
Most summits mark either relatively young vents or deeply eroded vent complexes.
Reversed polarized basaltic andesite, basalt, and andesite lava older than 0.73
million years are exposed in the walls of U-shaped canyons, but most of the
area is mantled my normally polarized rocks younger than 0.73 million years.
Most of the area is within the Mount Jefferson Wilderness.
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Learn MORE Central Oregon High Cascades - Menu
From:
Brantley, 1994, Volcanoes of the United States: USGS General Interest
Publication
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Volcanoes are not randomly distributed over the Earth's surface. Most are
concentrated on the edges of continents, along island chains, or
beneath the sea forming long mountain ranges.
More than half of the world's active volcanoes
above sea level encircle the Pacific Ocean to form the circum-Pacific
"Ring of Fire."
In the past 25 years, scientists have developed a theory -- called
plate tectonics --
that explains the locations of volcanoes and their relationship to other
large-scale geologic features.
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According to this theory, the Earth's surface is made up of a patchwork of about
a dozen large plates that move relative to one another at speeds from less than
one centimeter to about ten centimeters per year (about the speed at which
fingernails grow). These rigid plates, whose average thickness is about 80
kilometers, are spreading apart, sliding past each other, or colliding with each
other in slow motion on top of the Earth's hot, pliable interior. Volcanoes
tend to form where plates collide or spread apart, but they can also grow in the
middle of a plate, as for example the Hawaiian volcanoes. ...
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In the Pacific Northwest, the
Juan de Fuca Plate
plunges beneath the North American Plate.
As the denser plate of oceanic crust is forced deep into the
Earth's interior beneath the continental plate, a process known as
subduction,
it encounters high temperatures and pressures that partially
melt solid rock. Some of this newly formed magma rises toward the Earth's
surface to erupt, forming a
chain of volcanoes (the Cascade Range)
above the subduction zone. ...
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[Map,20K,InlineGIF]
Map, Juan de Fuca Subduction - Juan de Fuca Ridge - Cascade Range
-- Modified from: Brantley, 1994
From:
Wood and Kienle, 1990, Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p., p.148-149,
Contribution by Charles A. Wood.
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This volcanic province has the best understood
tectonic setting in the western USA
because
subduction of remnants of the Farallon Plate
is apparently still driving continental arc volcanism. The Cascade
region is not a typical subduction zone, however, for there is very little
seismic evidence of active subduction (Weaver and Baker, 1988) and there is no
trench (McBirney and White, 1982). In fact, the existence of volcanic activity
in the Cascades is the best evidence for ongoing subduction.
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The remaining part of the Pacific Plate currently converging with the
American Northwest is the
Juan de Fuca Plate,
with small platelets at its northern (Explorer Plate) and southern
Gorda Plate) terminations. The Explorer Plate separated from the Juan de Fuca
approximately 4 million years ago and is apparently no longer being subducted
(Hyndman, et.al., 1979); the Gorda split away between 18 and 5 million
years ago (Riddihough, 1984). The present slow rate of convergence (3-4
centimeters per year) of the Juan de Fuca Plate is only about half its
value at 7 million years (Riddihough, 1984), which probably explains the reduced
seismicity, lack of a trench, and debatable decline in volcanic activity.
...
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Learn MORE about Plate Tectonics - Menu
From:
Foxworthy and Hill, 1982,
Volcanic Eruptions of 1980 at Mount St. Helens, The First 100 Days:
USGS Professional Paper 1249
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Mount St. Helens
is one of a group of high volcanic peaks that dominate the
Cascade Range between northern California and southern British Columbia.
The distribution of these volcanic peaks in a broad band that roughly
parallels the coastline is typical of the so-called
"Ring of Fire",
a roughly circular array of volcanoes located on islands, peninsulas, and the
margins of continents that rim the Pacific Ocean.
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Even before it began erupting in 1980, Mount St. Helens
and at least six
other volcanoes in the Cascade Range were know the be "active" - that is, to
have erupted at least once during historical time. Few major Cascade volcanoes
are known to have been inactive long enough to be considered "extinct" or
incapable of further eruption. Most display some evidence of residual volcanic
heat, such as
fumaroles,
hot springs, or
hot ground where snow melt is unusually rapid. ...
Dramatic eruptive activity in the Cascades has been rare so far in the 20th
century. Until the
recent eruptions at Mount St. Helens,
the only Cascade volcano that had a major eruption during this century was
Lassen Peak in California.
A series of
intermittent eruptions
of steam and volcanic ash beginning in May
1914 and lasting until 1921 climaxed, during the 4 days from May 19 to 22, 1915,
in a series of violent events comprising small
lava flows,
massive lava-triggered
mudflows,
and
explosive eruptions of ash. ...
From the time when Lassen Peak quieted until March 1980, the only other
known increase in activity at a Cascade volcano occurred at
Mount Baker,
when a sudden increase in emanations of heat, steam, and other gases from a
previously steaming old crater
began on March 10, 1975.
Although new fumaroles were formed and minor amounts of "volcanic dust" and
sulfur were emitted, "the greatest undesirable natural results" that were
observed at Mount Baker
were "an increase in local atmospheric pollution and a
decrease in the quality of some local water resources" (Bortleson and others,
1977, p.B1). Since 1976, however, even those effects have subsided to levels
only slightly higher than those that prevailed before 1975.
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Eruptions of Cascade volcanoes tend to be much more explosive than those of, for
example, the well-known
Hawaiian volcanoes.
This explosive tendency is related to the chemical composition of
magma
that feeds the volcanoes and to the amount of gas contained in the magma.
Magma from the more explosive volcanoes contains relatively large amounts of gas
and silicon and produces rocks such as andesite, dacite, or rhyolite. Magma
from the less explosive volcanoes contains smaller concentrations of gas and
silicon and produces basalt as well as andesite. Some Cascade volcanoes,
including Mount St. Helens, have had nonexplosive eruptions of andesite
and basalt, as well as explosive eruptions, in the past.
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The existence, position, and recurrent activity of the Cascade volcanoes are
generally though to be related to the convergence of
shifting crustal plates.
Holocene Volcanism in the Cascades
|
From:
Wood and Kienle, 1990, Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p., p.148-149,
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.
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Guffanti and Weaver (1988) used the locations of 2,821 vents shown on the maps of Luedke and
Smith (1981, 1982) to divide the Cascades into five segments, with a sixth extending
south-eastward across the
High Lava Plains.
They note a volcano gap between
Rainier and Glacier Peak which coincides with the shallowest dip (11 degrees)
of the Cascade subduction zone, and they also infer a change in the configuration of the
subducting slab between Shasta and Lassen. Even though their segment
boundaries differ from Hughes et.al. (1980), Guffanti and Weaver similarly find that a number
of otherwise inexplicable features of Cascade volcanism are controlled by segmentation.
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Some researchers (e.g., Christiansen and Lipman, 1972) have suggested that
Sutter Buttes
and the Sonoma and
Clear Lake
volcanics, south and southwest of Lassen, are older extensions of subduction-related
Cascade volcanism. this seems unlikely. If Sutter Buttes were part of a series of
older Cascade stratovolcanoes abandoned due to the northward migration of the south end of
Juan de Fuca Plate, the "last Cascade volcano" hypothesis would be tenable. But
northward, arc volcanoes are young and active. In fact, why do the Cascades have such an
abrupt southern termination?
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The Clear Lake and Sonoma volcanics are the <5 million year components of a
northwesterly younging line of volcanic fields of Tertiary to Holocene age (Hearn, et.al.,
1981). All these volcanics lie within the San Andreas fault system, which appears to
have provided magma access to the surface. Hearn, et.al., point out that the timing of the
volcanism suggests that it follows termination of subduction, as the Mendocino triple
junction migrated northward. They also propose that the volcano alignment reflects an
underlying
hot spot.
That suggestion seems inconsistent with the northward movement of the Pacific Plate
which most of the volcanics ride. These volcanics are among the closest to a subduction
plate boundary of any in the world and will repay closer tectonic investigation. similarly, a
tiny sliver of basalt dated at 3.57 million years (Prowell, 1974, quoted in Luedke and Smith,
198) occurs 45 kilometers east of Santa Cruz, California, near the Calaveras and Hayward
faults. Apparently leakage of basalts along the San Andreas fault system has occurred
repeatedly.
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 3,000 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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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.
Earthquakes and Seismicity
|
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. ...
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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Cascade Range Earthquakes and Seismicity Menu
From: Scott, et.al., 1995, Volcano Hazards in the Mount Adams Region, Washington USGS Open-File Report 95-492.
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Mount Adams,
one of the largest volcanoes in the Cascade Range, dominates the Mount Adams volcanic field in Skamania,
Yakima, Klickitat, and Lewis counties and the Yakima Indian Reservation of south-central Washington. The nearby Indian Heaven
and Simcoe Mountains volcanic fields lie west and southeast, respectively, of the 1,250 square kilometers (500 square miles) Adams
field. Even though Mount Adams has been less active during the past few thousand years than neighboring Mounts St. Helens,
Rainier, and Hood, it assuredly will erupt again. Future eruptions will probably occur more frequently from vents on the summit and
upper flanks of Mount Adams than from vents scattered in the volcanic fields beyond. Large landslides and lahars that need not be
related to eruptions probably pose the most destructive, far-reaching hazard of Mount Adams.
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Mount Adams Menu
From: Gardner, et.al., 1995, Potential Volcanic Hazards from Future Activity of Mount Baker, Washington, USGS Open-File
Report 95-498
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Mount Baker
(3,285 meters; 10,778 feet) is an ice-clad volcano in the North Cascades of Washington State about 50 kilometers (31
miles) due east of the city of Bellingham. After Mount Rainier, it is the most heavily glaciated of the Cascade volcanoes: the volume
of snow and ice on Mount Baker (about 1.8 cubic kilometers; 0.43 cubic miles) is greater than that of all the other Cascades
volcanoes (except Rainier) combined. Isolated ridges of lava and hydrothermally altered rock, especially in the area of Sherman
Crater, are exposed between glaciers on the upper flanks of the volcano: the lower flanks are steep and heavily vegetated. The
volcano rests on a foundation of non-volcanic rocks in a region that is largely non-volcanic in origin.
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Mount Baker Menu
From: U.S. National Park Service, Crater Lake National Park Website, 2001
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Crater Lake
is located in Southern Oregon on the crest of the Cascade Mountain range, 100 miles east of the Pacific
Ocean. It lies inside a caldera, or volcanic basin, created when the 12,000-foot-high Mount Mazama collapsed 7,700
years ago following a large eruption.
Generous amounts of winter snow, averaging 533 inches per year, supply the lake with water. There are no inlets or
outlets to the lake. Crater Lake, at 1,958 feet deep, is the seventh deepest lake in the world and the deepest in the
United States. Evaporation and seepage prevent the lake from becoming any deeper.
The lake averages more than five miles in diameter, and is surrounded by steep rock walls that rise up to 2,000 feet
above the lake's surface.
Following the collapse of Mount Mazama, lava poured into the caldera even as the lake began to rise. Today, a small volcanic island,
Wizard Island, appears on the west side of the lake. This cinder cone rises 760 feet above the lake and is surrounded
by black volcanic lava blocks. A small crater, 300 feet across and 90 feet deep, rests on the summit. The
crater is filled by snow during the winter months, but remains dry during the summer.
The lake level fluctuates slightly from year to year. The highest level was reached in 1975 when the water level rose to 6,179.34 feet
above sea level. The lowest level was recorded in 1942 when it dropped to 6,163.20 feet. For
such a deep lake, the maximum observed variation of 16 feet is minor (less than 1 percent).
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Crater Lake Menu
Mount Garibaldi, British Columbia
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From: Geological Survey of Canada Website, Terrain Sciences Division, Natural Resources Canada, March 2001
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The alpine meadows, glaciers, and striking blue lakes of Garibaldi Provincial Park are set in a volcanic landscape of lava flows and
cinder cone volcanoes. These landforms record the interaction of volcanic eruptions with glacial ice. The most recent volcanic
activity occurred during the last Ice Age that ended 10,000 years ago.
Mount Garibaldi,
an eroded volcano, towers two and a half kilometers above downtown Squamish. Mount Garibaldi was built by
violent volcanic eruptions 15 to 20 thousand years ago when the Squamish Valley was filled with a large glacier. Volcanic debris that
formed the western flank of the volcano spread across the surface of the glacier. When the glacier later melted, the western side of
the volcano collapsed into the Squamish Valley.
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Canada Volcanoes and Volcanics Menu
From: Mastin and Waitt, 2000, Glacier Peak -- History and Hazards of a Cascade Volcano: USGS Fact Sheet 058-00
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Glacier Peak
is the most remote of the five active volcanoes in Washington State. It is not prominently visible from any major population center, and so its attractions, as well as its hazards, tend to be over-looked. Yet since the end of the last ice age, Glacier Peak has produced some of the largest and most explosive eruptions in the state. During this time period, Glacier Peak has erupted multiple times during at least six separate episodes, most recently about 300 years ago.
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Glacier Peak Menu
From: Scott, et.al., 1997, Volcano Hazards in the Mount Hood Region, Oregon: USGS Open-File Report 97-89
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Snow-clad
Mount Hood
dominates the Cascade skyline from the Portland metropolitan area to the wheat fields of Wasco and
Sherman Counties. The mountain contributes valuable water, scenic, and recreational resources that help sustain the agricultural and
tourist segments of the economies of surrounding cities and counties. Mount Hood is also one of the major volcanoes of the Cascade
Range, having erupted repeatedly for hundreds of thousands of years, most recently during two episodes in the past 1,500 years. The
last episode ended shortly before the arrival of Lewis and Clark in 1805. When Mount Hood erupts again, it will severely affect areas
on its flanks and far downstream in the major river valleys that head on the volcano. Volcanic ash may fall on areas up to several
hundred kilometers downwind.
Eruptive activity at Mount Hood during the past 30,000 years has been dominated by growth and collapse of lava domes. The last
two episodes of eruptive activity occurred 1,500 and 200 years ago. Repeated collapse of lava domes extruded near the site of
Crater Rock, Mount Hood's youngest lava dome, generated pyroclastic flows and lahars and built much of the broad smooth fan on
the south and southwest flank of the volcano.
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Mount Hood Menu
From: Walder, et.al., 1999, Volcano Hazards in the Mount Jefferson Region, Oregon: USGS Open-File Report 99-24
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Mount Jefferson
is a prominent feature of the landscape seen from highways east and west of the Cascades. Mount Jefferson
(one of thirteen major volcanic centers in the Cascade Range) has erupted repeatedly for hundreds of thousands of years, with its
last eruptive episode during the last major glaciation which culminated about 15,000 years ago. Geologic evidence shows that Mount
Jefferson is capable of large explosive eruptions. The largest such eruption occurred between 35,000 and 100,000 years ago, and
caused ash to fall as far away as the present-day town of Arco in southeast Idaho. Although there has not been an eruption at Mount
Jefferson for some time, experience at explosive volcanoes elsewhere suggests that Mount Jefferson cannot be regarded as extinct.
If Mount Jefferson erupts again, areas close to the eruptive vent will be severely affected, and even areas tens of kilometers (tens of
miles) downstream along river valleys or hundreds of kilometers (hundreds of miles) downwind may be at risk.
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Mount Jefferson Menu
From: U. S. National Park Service Website, Geology Fieldnotes - Lassen Volcanic National Park, California, April 2000
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Before the 1980 eruption of Mount St. Helens in Washington,
Lassen Peak
was the most recent volcanic outburst in the contiguous
48 states. The peak is the southernmost volcano in the Cascade Range which extends from here into Canada. The western part of
the park features great lava pinnacles (huge mountains created by lava flows), jagged craters, and steaming sulphur vents. It is cut by
spectacular glaciated canyons and is dotted and threaded by lakes and rushing clear streams. Snowbanks persist year-round and
beautiful meadows are spread with wildflowers in spring. The eastern part of the park is a vast lava plateau more than one mile
above sea level. Here are found small cinder cones (Fairfield Peak, Hat Mountain, and Crater Butte). Forested with pine and fir,
this area is studded with small lakes, but it boasts few streams. Warner Valley, marking the southern edge of the Lassen Plateau,
features hot spring areas (Boiling Springs Lake, Devils Kitchen, and Terminal Geyser). This forested, steep valley also has
gorgeous large meadows. ...
The Lassen geothermal area -- Sulphur Works, Bumpass Hell (largest), Little Hot Springs Valley, Boining Springs Lake,
Devils Kitchen, and Terminal Geyser -- offer bubbling mud pots, steaming fumaroles, and boiling water. Some of these thermal
features are getting hotter.
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Lassen Peak Menu
Meager Mountain, British Columbia
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From: Geological Survey of Canada Website, Terrain Sciences Division, Natural Resources Canada, March 2001
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Mount Meager
is a dormant volcano. However, about 2,400 years ago it erupted a great volcanic cloud that deposited ash as far east as Alberta. The eruption was similar in size to the 1980 eruption of Mount St. Helens. The earth beneath Mount Meager is hot. Surface waters seep under the volcano and become heated, then rise along fractures to reach the surface as hot springs. Holes have been drilled to 3,000 meters below the mountain to test this hot water plumbing system as a geothermal energy source. When hot water rises quickly in a drill hole it changes to steam; the force of this expanding steam can be used to generate electricity.
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Canada Volcanoes and Volcanics Menu
Medicine Lake, California
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From: U.S. National Park Service Website, Lava Beds National Monument, 2001
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The
Medicine Lake shield volcano,
a sleeping giant, is the largest volcano in the Cascade Range. Filling up the entire southern
skyline, it has been erupting off and on for half a million years. The eruptions were gentle rather than explosive like Mount St.
Helens, coating the volcano's sides with flow after flow of basaltic lava. This created a shield-shaped mountain approximately 150
miles around the base and 7900 feet high. Medicine Lake is part of the old caldera, a bowl-shaped depression in the mountain. It is
believed that the Medicine Lake volcano is unique, having many small magma chambers rather than one large one.
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Medicine Lake Menu
From: MacLeod, et.al., 1981, Newberry Volcano, Oregon: IN: Guides to Some Volcanic Terranes in Washington, Idaho, Oregon,
and Northern California: USGS Circular 838
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Newberry Volcano,
centered about 20 miles southeast of Bend, Oregon, is among the largest Quaternary volcanoes in thee
conterminous United States. It covers and area in excess of 500 square miles, and lavas from it extend northward many tens of miles
beyond the volcano. The highest point on the volcano, Paulina Peak with an elevation of 7,984 feet, is about 4,000 feet higher than
the terrain surrounding the volcano. The gently sloping flanks, embellished by more than 400 cinder cones, consist of basalt and
basaltic andesite flows, andesitic to rhyolitic ash-flow and air-fall tuffs and other types of pyroclastic deposits, dacite to rhyolite
domes and flows, and alluvial sediments produced during periods of erosion of the volcano. At Newberry's summit is a 4- to
5-mile-wide caldera that contains scenic Paulina and East Lakes. The caldera has been the site of numerous Holocene eruptions,
mostly of rhyolitic composition, that occurred as recently as 1,400 years ago. ...
Newberry lies 40 miles east of the crest of the Cascade Range in a setting similar to Medicine Lake Volcano in California.
Both volcanoes have the same shape, are marked by summit calderas, contain abundant rhyolitic domes
and flows, have widespread ash flows in addition to the more areally extensive basalt and basaltic-andesite flows and their related
cinder cones, have similar petrochemistry, and have been the sites of eruptions of pumiceous tephra and obsidian flows during the last
few thousand years.
Newberry lies at the west end of the High Lava Plains, a terrain formed of Miocene to Quaternary basalt flows and vents
punctuated by rhyolitic domes and vent complexes.
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Newberry Caldera Menu
Mount Rainier, Washington
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From:
Thomas W. Sisson, 1995,
History and Hazards of Mount Rainier, Washington:
USGS Open-File Report 95-642
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Mount Rainier is an active volcano that first erupted about half a million
years ago. Because of Rainier's great height (14,410 feet above sea level)
and northerly location, glaciers have cut deeply into its lavas, making it
appear deceptively older than it actually is. Mount Rainier is known to
have erupted as recently as in the 1840s, and large eruptions took place as
recently as about 1,000 and 2,300 years ago.
Mount Rainier and other similar volcanoes in the Cascade Range, such as
Mount Adams and Mount Baker, erupt much less frequently than the more
familiar Hawaiian volcanoes, but their eruptions are vastly more destructive.
Hot lava and rock debris from Rainier's eruptions have melted snow
and glacier ice and triggered debris flows (mudflows) - with a consistency
of churning wet concrete - that have swept down all of the river valleys that
head on the volcano. Debris flows have also formed by collapse of unstable
parts of the volcano without accompanying eruptions. Some debris flows have
traveled as far as the present margin of Puget Sound, and much of the lowland
to the east of Tacoma and the south of Seattle is formed of pre-historic
debris from Mount Rainier
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Mount Rainier Menu
From: Miller, 1980, Potential Hazards from Future Eruptions in the Vicinity of Mount Shasta Volcano, Northern California: USGS
Bulletin 1503
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Mount Shasta
is located in the Cascade Range in northern California about 65 kilometers (40 miles) south of the Oregon-California
border and about midway between the Pacific Coast and the Nevada border. One of the largest and highest of the Cascade
volcanoes, snowclad Mount Shasta is near the southern end of the range that terminates near Lassen Peak. Mount Shasta is a
massive compound stratovolcano composed of overlapping cones centered at four or more main vents; it was constructed during a
period of more than 100,000 years. Each of the cone-building periods produced pyroxene-andesite lava flows, block-and-ash flows,
and mudflows originating mainly at the central vents. ... Construction of each cone was followed by eruption of domes and
pyroclastic flows of more silicic rock at central vents, and of domes, cinder cones, and lava flows at vents on the flanks of the cones.
Two of the main eruptive centers at Mount Shasta, the Shastina and Hotlum cones were constructed during Holocene time, which
includes about the last 10,000 years. Holocene eruptions also occurred at Black Butte, a group of overlapping dacite domes about 13
kilometers (8 miles) west of Mount Shasta. ...
The communities of Weed, Mount Shasta, and McCloud ... are situated on the broad apron at the base of the volcano. A fourth
nearby community Dunsmuir ..., is located in the canyon of the Sacramento River about 23 kilometers (15 miles) south of Mount
Shasta.
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Mount Shasta Menu
Mount St. Helens, Washington
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From: Simon, 1999, Channel and Drainage-Basin Response of the Toutle River System in the Aftermath of the 1980 Eruption of
Mount St. Helens, Washington: USGS Open-File Report 96-633
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The 1980 eruptions of
Mount St. Helens
in southwestern Washington marked the re-awakening of a relatively young (40,000 years)
volcano that had been dormant since 1857. Frequent dacitic eruptions during the previous 2,500 years had produced pyroclastic flows,
ash falls, debris flows, lava domes, and lava flows of andesite and basalt. Pyroclastic flows and lahars accompanied most eruptive
periods and were largely responsible for forming fans around the base of the volcano, some of which dammed the North Fork Toutle
River to form Spirit Lake between 3,300 and 4,000 years ago. The magnitudes of the 1980 eruptions were not exceptional by
worldwide historical standards; however, they were the first volcanic eruptions in the conterminous United States since 1914 (Lassen
Peak) and focused national attention on events leading up to the climactic eruption of May 18, 1980. That eruption led to exceptional
opportunities for scientific observations, data collection, and the study of infrequent and often inaccessible geologic events and
processes.
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Mount St. Helens Menu
From: Scott, et.al., 2001, Volcano Hazards in the Three Sisters Region, Oregon: USGS Open-File Report 99-437
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Three Sisters
is one of three potentially active volcanic centers that lie close to rapidly growing communities and resort areas in Central Oregon. Two types of volcanoes exist in the Three Sisters region and each poses distinct hazards to people and property. South Sister, Middle Sister, and Broken Top, major composite volcanoes clustered near the center of the region, have erupted repeatedly over tens of thousands of years and may erupt explosively in the future. In contrast, mafic volcanoes, which range from small cinder cones to large shield volcanoes like North Sister and Belknap Crater, are typically short-lived (weeks to centuries) and erupt less explosively than do composite volcanoes. Hundreds of mafic volcanoes scattered through the Three Sisters region are part of a much longer zone along the High Cascades of Oregon in which birth of new mafic volcanoes is possible.
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Three Sisters Menu
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If you have questions or comments please contact:
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12/15/04, Lyn Topinka