Crater Lake

A half-circle view from the center of Crater Lake looking north towards the caldera.

NPS/photo by Kim Chamales 2021

First There Was a Mountain

A massive eruption occurred about 7,700 years ago. It was followed by ejections of volcanic matter through fractures, in an oval shape around the mountain. These events weakened the mountain's structure, and caused the central portion of Mount Mazama to collapse inward. The result was an 5–6 mi (8–10 km) diameter and 0.7 mi (1.2 km) deep caldera.

Before the collapse, Mount Mazama loomed at approximately 12,000 ft (3,658 m) tall. Today, the highest point along the rim is Hillman Peak at 8,151 ft (2,484 m) and the highest point in the park is Mount Scott at 8,929 ft (2722 m).
A full view from afar of Crater lake showing caldera and Wizard Island
Wizard Island is one of the most notable features of Crater Lake. It began developing before rain and snow started to fill the caldera.

NPS Photo/Kim Chamales

Now There is a Lake

Soon after the caldera formed, eruptions from new vents built the base of Wizard Island, and over several hundred years, rain and snow partially filled the caldera. Meanwhile, Wizard Island continued to grow and three other volcanoes formed underwater. The final eruption was on the east flank of Wizard Island about 4,800 years ago.

Evaporation and seepage are equal forces which keep Crater Lake from filling beyond an average depth of 1,943 ft (592 m) or 4.9 trillion gal (18.6 trillion L) of water. About 34 billion gal (128 billion L) are gained and lost each year. The yearly average snowfall on Crater Lake, as of 2020, is 42 ft (13 m) with an average yearly precipitation (rain and melted snow) of 67 in (2 m). Average snowfall has been decreasing since the 1930's when it was recorded at 51 ft (16 m).

Widely known for its rich blue color and extreme clarity, which averages 102 ft (31m) deep, Crater Lake is the deepest lake in the United States. It is one of the top ten deepest in the world. Unlike other Cascade Mountain lakes, Crater Lake rarely freezes over in the winter due to the heat content of the enormous water volume. To learn about lake ecology, current research, and the Long-term Limnological Monitoring Program, visit Crater Lake Research.

Beyond Blue

The mystique of Crater Lake begins with the public’s fascination of the lake's color, depth, and clarity. The lake's formation and  existence is explained through a collaboration of many sciences, along with human stories and experiences. Click on one of the items below for information about some of the lakes features and past explorations. Click here to access a yearly account of the Crater Lake Long-term Limnological Monitoring Program.
State of the Lake Report: 2020.

Curiosity abounds about life in Crater Lake. Well... mostly, people want to know if there are fish in the lake. Yes, there are nonnative fish, but what else?
  • Mazama Newts (Taricha granulosa mazamae) are endemic to Crater Lake. They have been isolated within the caldera for many generations, and are known as the top lake predator prior to the introduction of fish and crayfish. As a sub-species of rough-skinned newts which have a red belly and paralyzing toxin in their skin, Mazama Newts evolved to display less red and fewer toxins. 
  • Crater Lake is home to 160 taxa of phytoplankton and 12 taxa of zooplankton. Free-floating phytoplankton form the base of the food-chain in deep lakes. They support larger organisms, such as zooplankton, which in turn are food for even larger organisms like Kokonee salmon.
  • Other lifeforms include worms and insect larvae.
  • Seven species of fish were introduced into the lake between 1886 an 1941. Only two survived, Rainbow Trout and Kokonee Salmon. 
  • Crayfish were introduced in 1915 as food for nonnative fish. Over the last several decades they have spread to a significant portion of the shoreline. This expansion continues to impact the habitats and life cycles of Mazama newts. More recently, as crayfish spread, the shoreline of Crater Lake appears to be greening due to excessive algae growth. 
Further your understanding of Crater Lake by reading the State of the Lake Report: 2020. 

Hidden beneath the lake's surface between 85-460 ft (26-140 m) deep, moss hangs like icicles. It thrives on the near vertical walls of the caldera and forms thick fields on gentler slopes around Wizard Island. The moss was first discoverred and sampled during the Deep Rover Submarine Program in 1988-89. This deep-water moss is believed to represent the bulk of the biomass in Crater Lake.

A remarkable feature of the moss, are the thick deposits of peat—up to 30 feet (9 m)—created by centuries of moss growth. Lake biologists knew it existed because the peat occurs in relatively shallow water around Wizard Island. Some of these mats have holes, called fumeroles, wide and deep enough for divers to explore.

Click on this link to see a video of the moss.  

In the summers of 1987,' 88 and '89, the National Park Service, US Geological Survey, and National Geographic Society teamed up to lease a submarine called Deep Rover. With one researcher aboard, Deep Rover made 47 dives to the bottom. The purpose was to collect data on the lake’s hydrology, biology, and geology and to resolve a controversy over geothermal energy development that was brewing on the borders of the national park. A few of the discoveries include:
  • Colonies of yellow-gold bacteria grow in vast, puffy mats, often around pools of aqua-blue water. The bacteria are surviving in the darkness by oxidizing iron for energy. The iron comes from below via warm hydrothermal fluids.  
  • The warm hydrothermal fluids are greatly enriched in elements such as manganese, radon, lithium, and helium-3, indicating that they have had contact with hot, subterranean rock. 
  • Rock spires, chimneys made of silica that had precipitated out of other upwelling fuids at some point in the past
  • A variety of worms, insects, and tiny crustaceans, remarkable for their ability to tolerate the extreme water pressures found 1,943 feet (592 meters) below the surface.
  • Adult flies of the genus Heterotrissocladius, drop their eggs into the lake. The eggs sink slowly to the bottom, hatch into larvae, feed on lake foor sediments for two or three years, swim back up to the surface pupating along the way, then emerge as winged adults.
More information is available on the website at Underwater Exploration in Crater Lake.

Is it a mystery, a phenomenon, or simply part of a tree that is vertical and drifting around the lake?
Perhaps the Old Man of the Lake  is all three as its character simultaneously delights and eludes visitors hoping to see him from the rim. 
  • The Old Man is a 30-foot mountain hemlock log with three feet above water.
  • It was first sighted and tracked in 1896 by lake geologist, Joseph Diller. He described it as "a spectacle curious enough to ignite the imagination."
  • The Old Man’s age is carbon dated beyond 450 years old.
  • Although the Old Man has been dated, and observed and photographed for decades, it is unknown when it entererd the lake, becoming part of the lake's lore. 

Click on the link for photos and stories about the Old Man.

An automated weather station is attached to a buoy near the deepest part of Crater Lake. It reports hourly data to a publicly available website operated by the University of Utah - Department of Atmospheric Sciences. The data obtained from this weather station assists park researchers in understanding climate change, the effects of air and water temperature on lake currents, and other significant lake developments. The following data is collected by the weather station:
  • air temperature
  • dew point
  • wet bulb temperature
  • relative humidity
  • wind speed
  • wind gusts
  • water temperature - The sensor used for tracking surface water temperature is located under the buoy at a depth of approximately 3 ft (1m). 

Last updated: September 8, 2023

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Crater Lake National Park
PO Box 7

Crater Lake, OR 97604


541 594-3000

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