Crater Lake is a caldera lake located in the U.S. state of Oregon. It is the main feature of Crater Lake National Park and famous for its deep blue color and water clarity.

The lake partly fills a nearly 1,958 foot (597 m) deep caldera that was formed around 7,700 (± 150) years ago by the collapse of the volcano Mount Mazama.

On June 12, 1853, John Wesley Hillman was reportedly the first European American to see what he named "Deep Blue Lake" in Oregon. The lake was renamed at least three times, as Blue Lake, Lake Majesty, and finally Crater Lake.

Crater Lake is known for the "Old Man of the Lake", a full-sized tree that has been bobbing vertically in the lake for more than a century.[5] Due to the cold water, the tree has been rather well preserved.

While having no indigenous fish population, the lake was stocked from 1888 to 1941 with a variety of fish. Several species have formed self sustaining populations.

The commemorative Oregon State Quarter, which was released by the United States Mint in 2005, features an image of Crater Lake on its reverse.

The lake is 5 by 6 miles (8 km × 10 km) across with an average depth of 1,148 feet (350 m). Its deepest point has been measured at 1,949 feet (594 m) deep,[1] though as with any lake its depth fluctuates with the climate, particularly rainfall.

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 ninth deepest lake in the world (Lake Baikal is the deepest). Crater Lake is often cited as the 7th deepest lake in the world, but this ranking excludes Lake Vostok, which is situated under nearly 13,000 feet (4,000 m) of Antarctic ice, and the recent soundings of San Martín Lake, which is located on the border of Chile and Argentina.

However, on the basis of comparing average depths among the world's deepest lakes, Crater Lake becomes the deepest lake in the Western Hemisphere and the third deepest in the world. Comparing average depths among the world's lakes whose basins are entirely above sea level, Crater Lake is the deepest.

The caldera rim of Crater Lake ranges in elevation from 7,000 to 8,000 feet (2,100 to 2,400 m).

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 led to the subsidence of Mount Mazama around 5700 BC: about 50 cubic kilometers (12 cubic miles) 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.

Eventually, 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 lake bed. Fumaroles and hot springs remained common and active during this period. Also after some time, the slopes of the lake's caldera rim more or less stabilized, streams restored a radial drainage pattern on the mountain, and dense forests began to revegetate the barren landscape. It is estimated that about 720 years was required to fill the lake to its present depth of 594 m. Much of this occurred during a period when the prevailing climate was less moist than at present.

Some hydrothermal activity remains along the lake floor, suggesting that at some time in the future Mazama may erupt once again
Due to several unique 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-20 meter to mid-30 meter (80–115 ft) 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 has relatively high levels of dissolved salts, total alkalinity, and conductivity. The average pH has generally ranged between 7 and 8.

The Klamath tribe of Native Americans, who may have witnessed the collapse of Mount Mazama and the formation of Crater Lake, have long regarded the lake as a sacred site. Their legends tell of a battle between the sky god Skell and Llao, the god of the underworld.

Mount Mazama was destroyed in the battle, creating Crater Lake. The Klamath people used Crater Lake in vision quests, which often involved climbing the caldera walls and other dangerous tasks. Those who were successful in such quests were often regarded as having more spiritual powers. The tribe still holds Crater Lake in high regard as a spiritual site.


The following diagrams show the formation of Crater Lake during the climactic eruption of Mount Mazama. Diagrams are by Charles Bacon, acquired from the 1988 editon of the 1:62,500 scale topographic map entitled "Crater Lake National Park and Vicinity, Oreg."





Figure A: Plinian eruption deposits airfall pumice and ash, blown by winds to north and east.


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Figure B: Vent enlarges and eruption column collapses; pyroclastic flows deposit the Wineglass Welded Tuff on north and east flanks.



Figure C: Roof of magma chamber collapses, forming caldera as new vents open above fractures; pyroclastic flows deposit pumice and ash on all flanks of Mount Mazama and in valleys below.



Figure D: Caldera has been partly filled with pumice and ash from the eruption shown in C and with blocks of rock from the caldera walls; weak, dying explosions within the caldera deposit ash on the caldera rim; pyroclastic-flow deposits develop fumaroles and gradually cool.

Figure E: Crater Lake today.
courtesy:http://oregonexplorer.info/craterlake/geology.html