Broken Top
2,789 meters
(9,152 feet)
Stratovolcano
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Broken Top - Complex Stratovolcano
Broken Top is a complex stratovolcano magnificently exposed by glacial erosion.
Pleistocene eruptions of basaltic andesite lava produced a broad shield
with a core of oxidized agglomerate invaded by dikes and sills. Subordinate
silicic magmas were erupted intermittently; andesite, dacite, and rhyodacite
lavas, intrusives, and pyroclastic flow deposits are associated with the
predominant mafic lavas from the lower flanks to the summit of the volcano. The
central crater of Broken Top was enlarged to a diameter of 0.8 kilometers,
probably by subsidence. The resulting depression was filled by thick flows of
basaltic andesite and eventually the summit cone was buried beneath a shroud of
thin, vesicular lavas. After the central conduit had congealed to a plug of
micronorite, the core of the volcano was subjected to hydrothermal alteration.
Glacial cirques have been carved into three sides of the mountain, revealing
internal structure. Holocene eruptive activity on the flanks has produced
basaltic cones, flows, and ash deposits interbedded with Neoglacial moraines and outwash.
-- Taylor, 1990, IN: Wood and Kienle
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Mount Bachelor, Oregon
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Mount Bachelor
2,763 meters
(9,065 feet)
Stratovolcano atop Shield Volcano
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Mount Bachelor Volcanic Chain
The Mount Bachelor volcanic chain
provides one example of the type and scale of
eruptive activity that has produced most of the High Cascades platform,
which consists chiefly of scoria cones and lava flows, shield volcanoes,
and a few steep-sided cones of basalt and basaltic andesite.
The chain is 25 kilometers long; its lava flows cover 250 square kilometers
and constitute a total volume of 30-50 cubic kilometers.
-- Scott and Gardner, 1990
Mount Bachelor Volcano
The Three Sisters area contains 5 large cones of Quaternary age--
North Sister,
Middle Sister,
South Sister,
Broken Top, and
Mount Bachelor.
... Mount Bachelor,
which is between 11,000 and 15,000 years old
is the youngest of these volcanoes in the Cascades.
-- Hoblitt, et.al., 1987
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Newberry Caldera, Oregon
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Newberry Caldera
2,434 meters
(7,985 feet -
Paulina Peak)
Shield Volcano, Caldera
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Newberry Volcano
Newberry volcano is a broad shield volcano located in central Oregon.
It has been built by thousands of eruptions, beginning about
600,000 years ago. At least 25 vents on the flanks and summit have
been active during several eruptive episodes of the past 10,000 years.
The most recent eruption 1,300 years ago produced the Big Obsidian
Flow. Thus, the volcano's long history and recent activity indicate
that Newberry will erupt in the future.
-- Sherrod, et.al., 1997
Newberry Caldera, Paulina Peak, Paulina and East Lakes
Newberry Volcano, centered about 20 miles southeast of Bend, Oregon, is
among the largest Quaternary volcanoes in the conterminous United States. It
covers an 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 ...
-- MacLeod, 1981
Newberry Basaltic Eruptions
Basaltic eruptions are well known from observations elsewhere, such
as at Hawaii, where spectacular fountains of spatter and cinders are
associated with lava flows. At Newberry, basaltic eruptions have occurred
repeatedly on the volcano's flanks and in the caldera. Typical products
of a basaltic eruption are the 7,000-yr-old cinder cone of Lava Butte
and its surrounding lava flows, located 10 kilometers (6 miles) south of Bend.
Basaltic eruptions commonly begin with lava fountains that
hurl cinders or spatter as far as 1 kilometers (0.6 miles) from the vent. Ejecta
are thrown aloft for hundreds to a few thousand meters. Large fragments
are expelled from the vent along ballistic trajectories, like artillery
shells. Smaller particles are carried by wind and convective updrafts. The
resulting deposits may be many meters thick near the vent and build
a steep-sided cinder cone, but they generally thin to a few millimeters
within 10 kilometers (6 miles) distance downwind. The chief hazard from ballistic
ejection is direct impact. Some spatter will be hot upon impact and
likely will start forest fires.
-- Sherrod, et.al., 1997
Big Obsidian Flow
The eruptive sequence that culminated in the Big Obsidian Flow 1,300
years ago exemplifies several aspects of a typical rhyolitic eruptive
sequence at Newberry volcano. The eruptions began with tephra showers
that deposited pumice lumps and dense lava blocks as large as 1 meter
(3 feet) within the caldera. ...
As the eruption progressed, pyroclastic flows swept downslope from
the Big Obsidian vent to Paulina Lake. The boat ramp at
Little Crater Campground is excavated in these pyroclastic-flow deposits,
as is the caldera road upslope from Paulina Lake. The flows entered
Paulina Lake, perhaps causing secondary steam explosions and displacing
water from the lake into Paulina Creek.
The final stage of eruption produced the Big Obsidian Flow itself,
a lava flow that moved slowly, probably advancing only a few meters
or tens of meters per day as it oozed down an inner caldera wall and
ponded on the caldera floor. The Big Obsidian Flow is about
1.8 kilometers (6,000 feet) long and locally thicker than 20 meters (65 feet).
-- Sherrod, et.al., 1997
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-- Sherrod, et.al., 1997, OFR97-513
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Lava Butte and Pilot Butte, Oregon
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Lava Butte
Lava Butte
1,544 meters
(4,970 feet)
Cinder Cone
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Lava Butte
This cinder cone rises 500 feet from the surrounding forest floor offering breathtaking views of
the Cascades. At the 5000-foot summit is a fire lookout and visitor rest area
with interpretive displays. Turn left from Lava Lands Visitor Center
parking and follow signs to Lava Butte. The Butte is closed to trailers due to
inadequate parking.
-- U.S. Forest Service Pamphlet, 1994
The basaltic andesite flow derived
from Lava Butte extends northward more than 5 miles and westward 3 miles to the
Deschutes River. ... It is one of many basaltic andesite flows on Newberry that
have carbon-14 ages of about 6,100 years. ...
The lava flow emerges from the south side of the butte.
-- Hoblitt, et.al., 1987
Pilot Butte
A cinder cone at the east city limits at Bend.
Visible from its easily accessible top are the
snow peaks of the Cascade Range
(listed from the north):
Mount Hood, 11,235 feet;
Mount Jefferson, 10,495 feet;
Three-Fingered Jack, 7,848 feet;
Mount Washington, 7,802 feet;
North Sister, 10,094 feet;
Middle Sister, 10,053 feet;
South Sister, 10,354 feet;
Broken Top, 9, 165 feet; and
Mount Bachelor Ski Resort Area, 9,600 feet.
-- Bend Chamber of Commerce, 1984
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Diamond Peak, Oregon
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Diamond Peak
2,667 meters
(8,750 feet)
Shield Volcano
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Diamond Peak Volcano
Diamond Peak, the dominant landform in the Willamette Pass area, is a
basaltic andesite shield
approximately 15 cubic kilometers in volume. Like other shields in the area, it
has a central pyroclastic cone that is surrounded and surmounted by lava
flows. Volcaniclastic rocks such as lahars and pyroclastic flows are unknown.
Diamond Peak began erupting from a vent near its northern summit. A second vent
later opened near the southern summit, piggy-backing its lava and tephra over
the previously erupted volcanic rocks. This vent migration likely involved only
a small interval of time. Diamond Peak is probably less than 100,000 years old,
but is certainly older than the last glaciation, which ended approximately
11,000 years ago.
-- Sherrod, 1990, IN: Wood and Kienle
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Mount Bailey, Oregon
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Mount Bailey
2,549 meters
(8,363 feet)
Shield Volcano
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Mount Bailey Volcano
Mount Bailey is the southernmost volcano in a north-south-trending
volcanic chain 10 kilometers long that rises west of Diamond Lake. Bailey
is about the same age as Diamond Peak, 43 kilometers north: less than
100,000 years but greater than 11,000 years old, on the basis of
glacial evidence and morphologic comparisons with dated volcanoes. Like Diamond
Peak, Bailey consists of a tephra cone surrounded by basaltic andesite lava.
Bailey is slightly smaller (8-9 cubic kilometers) than Diamond Peak, and minor
andesite erupted from the summit cone in its late stages, whereas Diamond Peak
eruptions were never more siliceous than basaltic andesite.
-- Sherrod, 1990, IN: Wood and Kienle
Mount Bailey Volcanic Chain
The Mount Bailey chain includes Rodley Butte and other
cinder cones to the north, all of which are similar in age (based on morphology) and
magmatically related (on the basis of mineralogy, chemistry, and close spatial
association of the vents). Volcanism along the Bailey chain migrated spatially
from north to south while it evolved chemically.
-- Sherrod, 1990, IN: Wood and Kienle
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Mount Thielsen, Oregon
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Mount Thielsen
2,799 meters
(9,182 feet)
Shield Volcano
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Mount Thielsen Volcano
Mount Thielsen is a normally polarized
shield volcano comprising approximately 8 cubic kilometers of basaltic andesite built
atop a broad pedestal (24 cubic kilometers) of older lava. Thielsen is remarkable even at
a distance for its colorfully interbedded pyroclastic rocks that dip away from the jagged
spire of the central plug, often called the "lightning rod of the Cascades". The most
spectacular views are on the north and east sides (accessible only by foot or horseback)
where now-vanished glaciers have carved precipitous cirque walls that reveal the
construction. Thielsen's age is approximately 290,000 years (whole-rock K-Ar), and
its geomorphology is a reference point for assigning Cascade Range volcanoes to the age
division 0-0.25 million years (younger than Thielsen) or 0.25-0.73 million years (older
than Thielsen). Very little of Thielsen's underpinnings are exposed because Holocene
Mazama ash, which erupted from vents at Crater Lake National Park
(20 kilometers south), forms a shroud 4-20 meters thick in the Thielsen area.
-- Sherrod, 1990, IN: Wood and Kienle
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Crater Lake, Oregon
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Crater Lake
2,487 meters
(8,156 feet -
Hillman Peak)
Stratovolcano -
Caldera
Lake Depth -
1,932 feet
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Crater Lake Caldera
The caldera now filled by Oregon's Crater Lake
was produced by an eruption that destroyed a volcano the size of Mount St. Helens.
-- Wright and Pierson, 1992
Crater Lake caldera formed by collapse during the catastrophic eruption
of approximately 50 cubic kilometers of magma, 6,845 carbon-14 years B.P. (before present).
The 8x10 kilometer caldera lies in the remains of Mount Mazama, a Pleistocene stratovolcano cluster
covering 400 square kilometers in the southern Oregon Cascades. Prior to its
climactic eruption, Mount Mazama's summit had an elevation between 3,300 meters
and 3,700 meters (10,800 - 12,000 feet).
Its southern and southeastern flanks were deeply incised by
glacial valleys, now beheaded, that form U-shaped notches in the caldera wall.
-- Bacon, 1990, IN: Wood and Kienle
Wizard Island
Post-caldera volcanic landforms are present beneath the lake surface and poke
through to form Wizard Island.
The central platform, Merriam Cone, and Wizard Island are all andesite evidently
erupted within a few hundred years of caldera collapse. The small rhyodacite dome
30 meters below lake level one kilometer east of Wizard Island is the
youngest feature.
-- Bacon, 1990, IN: Wood and Kienle
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-- Bacon, et.al., 1997, OFR97-487
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Mount McLoughlin, Oregon
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Mount McLoughlin
2,894 meters
(9,496 feet)
Shield Volcano
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Mount McLoughlin Volcano
Mount McLoughlin
(Mount Pit or Pitt) rises 1,200 meters as a steep-sided,
dominantly basaltic andesite lava cone above the low Pliocene and Pleistocene
basaltic andesite shields on which it is built. McLoughlin is easily recognized
from as far away as Medicine Lake in California,
along I-5 between Yreka, California, and Medford, Oregon, or around the rim of
Crater Lake. Although it is the tallest volcano between
Shasta and Crater Lake, McLoughlin, with a volume
of only 13 cubic kilometers, is dwarfed by the bulk of Shasta (350 cubic
kilometers) and Mazama (130 cubic kilometers [Crater Lake]).
-- Smith, 1990, IN: Wood and Kienle
Part of the Mountain is Missing
When viewed from the south or southeast it appears a seemingly perfectly
symmetrical Fuji-like volcano.
However, when seen from the east, along the
shores of Klamath Lake, or from the north along Crater Lake's rim, it is apparent
that a major part of the mountain is missing. Late Pleistocene glaciers have
carved away the entire northeast side of the mountain, lowering the summit about
a hundred meters, excavated the large bowl-like cirque, and exposed the
congealed lava that fills two small central conduits. Steeply dipping layers of
pyroclastic breccia and tuff and numerous interlayered lava flows are exposed in
the walls of the cirque. An explosive origin is sometimes ascribed to this
cirque; however, there is no evidence of deposits that would have resulted from
such an explosion. Glacial striae and other glacial features are common in the
cirque, and glacial deposits such as moraines and till are present at the mouth
of the cirque and around the north base of the mountain. Finally, the
composition of McLoughlin's lava is much more mafic than that of other volcanoes
at which explosive events of the required size have occurred.
-- Smith, 1990, IN: Wood and Kienle
A Young Volcano
Mount McLoughlin is a young volcano. A pronounced magnetic high centered just
east of McLoughlin's main vent is interpreted as indicating that most of the
main cone is normally polarized and thus less than approximately 700,000 years
old. The well preserved shape of the mountain's west and south flanks, the lack
of soil development on many flows, and preservation of primary flow features
suggests that the bulk of the main cone is no older than 200,000 years, with
much of it probably younger. The main cone was essentially complete before the
last major Pleistocene glaciation. Many flank flows are younger than the main
cone; some may be as young as 20,000 - 30,000 years.
-- Smith, 1990, IN: Wood and Kienle
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Medicine Lake, California
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