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Spirit Lake, once surrounded by lush forest, is within the area devastated by the May 18, 1980 blast. Remnants of the forest now float on the surface of the lake. Another Cascade volcano, Mount Rainier (14,410 feet [4,392 meters]), is in the distance. The view is from the south.
-- USGS Photo by Lyn Topinka, October 4, 1980

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Mount St. Helens reflected in Spirit Lake, May 19, 1992
-- USGS Photo by Lyn Topinka, May 19, 1992

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Mount Adams as viewed from Harrys Ridge, near Mount St. Helens, Washington. Lake in the foreground is Spirit Lake.
-- USGS Photo by Lyn Topinka, September 29, 1988

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Two USGS scientists (yellow circle) use a boat to take water samples from Spirit Lake in 1981. Logs and debris covered most of the surface of Spirit Lake.
-- USGS Photo by Lyn Topinka, July 16, 1981

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The May 18, 1980 debris avalanche from Mount St. Helens covered over 24 square miles (62 square kilometers) of the upper Toutle River valley and blocked tributaries of the North Fork Toutle River. New lakes such as Castle Lake (pictured here) and Coldwater Lake were created.
-- USGS Photo by Robert L. Schuster, March 1984

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Aerial view, Coldwater Lake, with debris avalanche hummocks in the foreground. Coldwater Ridge Visitor Center sits on the ridge to the west (left), overlooking the lake.
-- USGS Photo by Lyn Topinka, January 13, 1984

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One major concern to people living downstream of Mount St. Helens is a breakout of any of these impounded lakes due to the instability of the debris dams blocking them. Flood waters from a breakout could be more catastrophic than the lahars of May 18, 1980. Gages, such as this Early Warning Gage on Coldwater Lake, have been installed at lakes and streams surrounding the volcano. These gages continuously monitor changes in water levels. Major increases or decreases in levels trigger warnings which are telemetered to the U. S. Geological Survey in Vancouver.
-- USGS Photo by Lyn Topinka, October 1, 1982

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Outlet channels have been built at Castle Lake and Coldwater Lake (shown here) to stabilize water levels and prevent overtopping of the debris dams.
-- USGS Photo by Lyn Topinka, October 17, 1981

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Aerial view, Spirit Lake and Mount St. Helens, from the north, showing debris-avalanche-dam impounding the lake.
-- USGS Photo by Lyn Topinka, April 25, 1991

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Aerial view, Spirit Lake pump station. From late 1982 through the spring of 1985, a pump station operated at Spirit Lake to maintain that lake at a safe level. Without pumping, Spirit Lake was estimated to overtop its debris dam within a year.
-- USGS Photo by Lyn Topinka, September 23, 1983

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In the spring of 1985 a permanent tunnel was opened, allowing water to drain out of the lake safely. This tunnel is 11 feet (3.4 meters) in diameter and more than 1.5 miles (2.5 kilometers) in length. The water level of Spirit Lake is now maintained at approximately 100 feet (30 meters) below the estimated overtopping level.
-- USGS Photo by Lyn Topinka, October 2, 1986

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View across Silver Lake towards Mount St. Helens.
-- USGS Photo by Lyn Topinka, September 15, 1980

Silver Lake is shallow (maximum depth about 16 feet or 5 meters) and was formed and is partially underlain by lahar deposits. About 2,500 years ago during the Pine Creek eruptive period, a series of very large lahars traveled down the Toutle River from Mount St. Helens. The lahars flowed into Outlet Creek (east of the lake) and dammed its valley to produce Silver Lake. These lahars were generated by the catastrophic draining of a lake (presumably an older Spirit Lake) or lakes that had been dammed by debris avalanches from Mount St. Helens. The level of Silver Lake is now controlled by a dam. -- From: Pringle, 1993, Roadside Geology of Mount St. Helens National Volcanic Monument and Vicinity: Washington Department of Natural Resources Division of Geology and Earth Resources Information Circular 88.

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Aerial view, Swift Reservoir.
-- USGS Photo by Lyn Topinka, June 22, 1984

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