America's Volcanic Past -
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| "Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994 |
MORE America's Volcanic Past - Oregon
Visit A Volcano - Crater Lake National Park
Learn More About
Crater Lake
Learn More About
Oregon Volcanoes
Volcanic Highlights and Features:
[This list is just a sample of
various Crater Lake volcanic features or events and is by no means inclusive.]
Today, the calm beauty of Crater Lake belies the violent earth forces
that formed the lake. Crater Lake lies
inside the top of an ancient volcano known as Mount Mazama.
For half a million years this mighty volcano
produced massive eruptions
interrupting long periods of quiet. Ash, cinders, and pumice exploded upward,
building the mountain to a height of about 12,000 feet.
About 7,700 years ago the climatic eruptions of Mount Mazama occurred.
Ash from these eruptions lies scattered over eight states and three Canadian
provinces, some 5,000 square miles were covered with 6 inches of Mazama's ash.
In the park's Pumice Desert ash lies 50 feet deep. The eruptions were
42 times greater than those of Mount St. Helens in 1980. The Mazama
magma chamber was emptied and the volcano collapsed, leaving a huge bowl-shaped
caldera. The high mountain was gone. At first the caldera's floor was too hot to hold water.
The collapse of Mount Mazama marked the beginning of the formation of Crater Lake.
Snow and rain fell into the 3,000-foot deep hole, filling the collapsed structure.
Eventually, the lake reached a relatively constant level. Precipitation entering
the lake was offset by evaporation and seepage. Today, the lake level only
varies about three feet each year.
Crater Lake, at 1,958 feet (597 meters) deep,
is the seventh deepest lake in the world and the deepest in the
United States.
Excerpts from: U. S. National Park Service, Crater Lake National Park Website, 2001 |
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| Crater Lake National Park |
Mount Mazama and Crater Lake:1
Crater Lake was formed after the collapse of an ancient volcano, posthumously named Mount
Mazama. This volcano violently erupted approximately 7,700 years ago.
That eruption was 42 times as
powerful as the 1980 eruption of Mount St. Helens.
The basin or caldera was formed after the top 5,000
feet of the volcano collapsed. Subsequent lava flows sealed the bottom,
allowing the caldera to fill with
approximately 4.6 trillion gallons of water from rainfall and snow melt,
to create the seventh deepest lake in the world at 1,932 feet.
Today, Crater Lake is widely known for its intense blue color and spectacular views. During
summer, visitors may navigate the 33-mile Rim Drive around the lake,
enjoy boat tours on the lake surface,
stay in the historic Crater Lake Lodge,
camp at Mazama Village, or hike some of the park's various trails
including Mount Scott at 8,929 feet.
Crater Lake:1
Generous amounts of winter snow, averaging 533 inches
(1,354 centimeters) per year, supply the lake with water. There are no
inlets or outlets to the lake. Crater Lake, at 1,958 feet (597
meters) 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 (8 kilometers) in diameter,
and is surrounded by steep rock walls that rise up to 2000 feet
(600 meters) above the lake's surface.
| Chaski Bay Landslide |
Chaski Bay Landslide:3
Geologic evidence for the rapid formation of Crater Lake caldera by
catastrophic collapse during the climactic eruption of Mount Mazama
indicates that most of the caldera wall dates from that time. However, the
bench on the south wall, informally known as Chaski slide, wall-parallel
lake-facing scarps near Garfield Peak, and similar faults mapped in the
Sun Notch to Eagle Point area suggest that large blocks of the
south wall have the potential to fail. Nelson and other (1988, 1994)
described a landslide deposit on the lake
floor from Chaski Bay to the center of the lake that apparently formed
soon after the caldera collapse and the central platform volcano erupted but
before a deep lake was present.
| Cleetwood Flow |
Cleetwood Flow:6
Rhyodacite dome
| Discovery Point |
Discovery Point:1
Discovery Point is the site of John Wesley Hillman's "discovery" of Crater Lake in
1853.
| Grouse Hill |
Grouse Hill:6
Rhyodacite dome
| Hillman Peak |
Hillman Peak:1,4
Hillman Peak is the westernmost andesitic stratocone
in the cluster of polygenetic volcanoes that make up
Mount Mazama.
Hillman Peak is 1,980 feet (604 meters) above the water,
highest point on the caldera rim.
Stratovolcanoes and Shields:2
Individual stratovolcanoes and shields
that make up Mount Mazama become younger in a west-northwest sense. The oldest
Mazama lavas dated are flows near lake level at Phantom Ship and the lavas of
Mount Scott (around 400,000 years). The
youngest stratovolcano is Hillman Peak (around 70,000 years).
Local andesite flows on the north rim are 50-40,000 years old.
| Llao Rock |
Llao Rock:6
Rhyodacite dome
| Mount Scott |
Mount Scott:1
Mount Scott - highest peak in the park, historic fire tower, strenuous climb,
1,500 foot rise.
Stratovolcanoes and Shields:2
Individual stratovolcanoes and shields
that make up Mount Mazama become younger in a west-northwest sense. The oldest
Mazama lavas dated are flows near lake level at Phantom Ship and the lavas of
Mount Scott (around 400,000 years). The
youngest stratovolcano is Hillman Peak (around 70,000 years).
Local andesite flows on the north rim are 50-40,000 years old.
| Palisade Point |
Palisade Point:1
Palisade Point - is 507 feet (155 meters) above the water, lowest point on the caldera rim.
| Phantom Ship |
Stratovolcanoes and Shields:2
Individual stratovolcanoes and shields
that make up Mount Mazama become younger in a west-northwest sense. The oldest
Mazama lavas dated are flows near lake level at Phantom Ship and the lavas of
Mount Scott (around 400,000 years). The
youngest stratovolcano is Hillman Peak (around 70,000 years).
Local andesite flows on the north rim are 50-40,000 years old.
Phantom Ship:1
Phantom Ship is 167 feet (51 meters) above the water.
| Redcloud Flow |
Redcloud Flow:6
Rhyodacite dome
| Wizard Island and Merriam Cone |
Wizard Island:1
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 (233 meters) above the lake and is
surrounded by black volcanic lava blocks. A small crater, 300 feet (90 meters)
across and 90 feet (27 meters) deep, rests on the
summit. The crater is filled by snow during the winter months,
but remains dry during the summer.
|
Wizard Island and Merriam Cone:4
The only volcanic features in the Crater Lake area younger than the
climactic eruption occur within the caldera.
Merriam Cone, a small (approximately 0.1 cubic kilometer) olivine-bearing
andesitic vent on the north margin of the caldera floor, is the smallest of
three distinguishable volcanic features. Wizard Island forms the
subaerial part of a voluminous pile of presumably similar andesitic material.
The Wizard Island edifice accounts for approximately 1 to 2 cubic
kilometers of magma, depending on where its base is drawn. The broad
platform east of Wizard Island suggests silicic lava flows or coalescing domes.
At the west end of this platform is a small dome composed of hornblende
rhyodacite.
| America's Volcanic Past - Oregon |
Excerpts from:
1) U.S. National Park Service Website, 2001, Crater Lake National Park
2) Bacon, C.R., 1990, IN:
Wood and Kienle, 1990, Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p., p.193-195,
3) Bacon, et.al., 1997,
Volcano and Earthquake Hazards in the Crater Lake Region, Oregon:
USGS Open-File Report 97-487
4)
Bacon, C.R., 1983,
Eruptive History of Mount Mazama and Crater Lake Caldera, Cascade Range,
U.S.A.:
Journal of Volcanology and Geothermal Research, v.18 (1983), p.57-115
5)
Allen, J.E., 1985, Time Travel in Oregon: A scrapbook of geological articles published in 'The Oregonian' from
November 3, 1983 to October 31, 1985:
Department of Geology, Portland State University
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