Crater Lake

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Crater Lake, Oregon
Aerial view of Crater Lake, June 2004
Geologic map of the lake floor
Coordinates	42°56′N 122°08′W
Lake type	Volcanic Lake
Primary sources	Precipitation only
Primary outflows	Evaporation only
Basin countries	USA (Oregon)
Max-length	9.6 km
Max-width	8 km
Surface area	53.2 km²
Average depth	450m
Max-depth	589m
Water volume	17.46 km³
Shore length¹	35.1 km
Surface elevation	1,882.4 m
Islands	Wizard Island
¹ Shore length is an imprecise measure which may not be standardized for this article.

For the general term of a geological feature that goes by the same name, see crater lake.

Oregon quarter

Crater Lake is a lake in the U.S. state of Oregon that is 5 by 6 miles (8 by 9.6 km) and 1958 ft (597 m) deep. It is Crater Lake National Park's most prominent feature and is famous for its deep blue color and water clarity. The lake partly fills a nearly 4000 ft (1220 m) deep caldera that was formed around 7700 years ago by the collapse of the volcano Mount Mazama.

The lake's average depth is 1,148 ft (350 m). Its deepest point has been measured at 1949 ft (594 m) deep [1], though as with any lake its depth fluctuates with the climate, particularly rainfall [2]. This makes Crater Lake the deepest lake in the United States, the second deepest lake in North America (Great Slave Lake is the deepest) and the seventh deepest lake in the world (Lake Baikal is the deepest). It also holds the honor of being the deepest lake in the world that is completely above sea level. The caldera rim ranges in elevation from 7000 to 8000 ft (2130 to 2440 m). The average elevation of the lake's surface is 6178 ft (1883 m).

The lake is known for its vertical driftwood, named Old Man of the Lake.

The Oregon state quarter, released in 2005, features an image of Crater Lake.

[edit] Geology

View from the rim

Mount Mazama, part of the Cascade Range volcanic arc, was built up mostly of andesite, dacite, and rhyodacite over a period of at least 400,000 years. The caldera was created in a massive volcanic eruption that lead to the subsidence of Mount Mazama around 5700 BC: about 50 cubic kilometers of rhyodacite was erupted in this event. Since that time, all eruptions on Mazama have been confined to the caldera.

Lava eruptions later created a central platform, Wizard Island, Merriam Cone, and other, smaller volcanic features, including a rhyodacite dome that was eventually created atop the central platform. Sediments and landslide debris also covered the caldera floor.

In time, the caldera cooled, allowing rain and snow to accumulate and eventually form a lake. Landslides from the caldera rim thereafter formed debris fans and turbidite sediments on the lakebed. Fumaroles and hot springs remained common and active during this time.

In time, the slopes of the caldera rim more or less stabilized, streams restored a radial drainage pattern on the mountain, and dense forests revegetated the barren landscape.

Some hydrothermal activity remains at the lake floor, suggesting that someday in the future Mazama may erupt again. [3]

[edit] Water quality

The Old Man of the Lake (with extreme clarity of water apparent)

Due to several factors, most prominently that it has no inlets or tributaries, the waters of Crater Lake are some of the purest in terms of the absence of pollutants in North America.

Secchi disk clarity readings have consistently been in the high-20m to mid-30m range, which is very clear for any natural body of water. In 1997, scientists recorded a record clarity of 43.3 meters (142 ft). The lake traditionally has relatively high levels of dissolved salts, total alkalinity, and conductivity. The average pH has generally ranged between 7 and 8.

[edit] References

Fire Mountains of the West: The Cascade and Mono Lake Volcanoes, Stephen L. Harris, (Mountain Press Publishing Company, Missoula; 1988) ISBN 0-87842-220-X
Geology of National Parks: Fifth Edition, Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7
Eruptive history and geochronology of Mount Mazama and the Crater Lake region, Oregon, Charles R. Bacon and Marvin A. Lanphere, Geological Society of American Bulletin v. 118, p. 1331-1359 (2006) DOI: 10.1130/B25906.1

[edit] See also

Crater Lake Panorama, September 2005

Crater Lake From Visitors Center July 2005

[edit] External links

Crater Lake Data Clearinghouse of the United States Geological Survey
Diving into mysterious Crater Lake - CNET News.com (August 25, 2006)
Maps and aerial photos
- WikiSatellite view at WikiMapia
- Topographic map from TopoZone
- Aerial image from TerraServer-USA
- Surrounding area map from Google Maps
- Location in the United States from the Census Bureau