Crater Lake

North America's Deepest Lake, Born from a Cataclysmic Eruption

Elevation

2,487 m

Last Eruption

~2850 BCE

Type

Caldera

Country

United States

Location

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Volcanic Hazards & Risk Assessment

Primary Hazards

Pyroclastic flows and surges
Large explosive eruptions (VEI 4+)
Ash fall and tephra deposits
Lahars and debris flows

Risk Level

Population at RiskModerate

Infrastructure RiskHigh

Aviation RiskSignificant

Geological Composition & Structure

Rock Types

Primary

Unknown

Silica Content

Varied composition

Tectonic Setting

Unknown

Intraplate setting with hotspot or regional volcanic activity.

Age & Formation

Epoch

Unknown

Evidence

Unknown

Eruption Statistics & Analysis

Metric	Value	Global Ranking	Significance
Total Recorded Eruptions	Unknown	Low	Moderately active volcano
Maximum VEI	VEI Unknown	Minor	Local impact potential
Recent Activity	-824 years ago	Very Recent	Currently active

Monitoring & Alert Status

Monitoring Networks

USGS Volcano Hazards Program

Comprehensive monitoring network

Global Volcanism Program

International eruption database

Current Status

Active

Recent volcanic activity detected. Continuous monitoring in place.

Authority Sources

Smithsonian GVP

Official volcano database

USGS Volcano Hazards

U.S. Geological Survey

Related Volcanoes

All United States Volcanoes

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Caldera Volcanoes

By volcano type

Southern Oregon, Cascade Range

Regional volcanoes

A scenic view of a lake surrounded by trees

Forsaken Films

via Unsplash

a large body of water surrounded by mountains

Adrián Valverde

via Unsplash

Adrián Valverde

via Unsplash

Anukrati Omar

via Unsplash

brown mountain under blue sky during daytime

Ani Adigyozalyan

via Unsplash

a heart shaped hole in the middle of a mountain

Conor Murphy

via Unsplash

Other Volcanoes in United States

Akutan
Stratovolcano
Kilauea
Shield volcano
Mauna Loa
Shield volcano
Novarupta
Caldera

Interesting Facts

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Crater Lake is the deepest lake in the United States at 594 m (1,949 ft) and the ninth deepest in the world.

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The climactic eruption of Mount Mazama approximately 7,700 years ago ejected roughly 50 km³ of magma — making it one of the five largest eruptions in the last 10,000 years.

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The Mazama ash layer has been found in geological deposits over 1,500 km from Crater Lake and serves as a key stratigraphic marker across western North America.

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Crater Lake has no inlet or outlet streams — its water comes entirely from rain and snowfall, which is balanced by evaporation and seepage.

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The Klamath Tribes' oral tradition of the lake's creation, involving a battle between the spirits Llao and Skell, has been transmitted for nearly 8,000 years — one of the world's oldest verified geological oral histories.

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Crater Lake National Park, established in 1902, is the fifth oldest national park in the United States and the only one in Oregon.

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The lake's extraordinary blue color results from its extreme depth and clarity — water absorbs all visible wavelengths except blue, which scatters back to the observer.

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Secchi disk transparency measurements in Crater Lake have exceeded 40 m, making it one of the clearest lakes on Earth.

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Before its destruction, Mount Mazama is estimated to have stood approximately 3,400 m (11,200 ft) tall — comparable to modern Mount Rainier.

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The park receives an average of 13 m (43 ft) of snowfall annually, making it one of the snowiest inhabited locations in North America.

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Wizard Island, the cinder cone protruding above the lake surface, rises approximately 230 m above the waterline but extends roughly 500 m from its base on the caldera floor.

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Thermal springs discovered on the caldera floor during submersible dives in the 1980s confirm that a heat source persists beneath Crater Lake — the volcano is dormant, not extinct.

Frequently Asked Questions

How deep is Crater Lake?

Crater Lake reaches a maximum depth of 594 m (1,949 ft), making it the deepest lake in the United States and the ninth deepest in the world. The average depth is approximately 350 m (1,148 ft), and the lake's surface sits at 1,883 m (6,178 ft) elevation while the caldera rim rises to 2,487 m (8,159 ft) at its highest point. The lake contains approximately 18.7 km³ of water. Detailed bathymetric mapping was completed in 2000 using multibeam sonar, confirming the depth measurements first established by a team led by Major Clarence Dutton in 1886, who used a weighted piano wire lowered from a boat.

How was Crater Lake formed?

Crater Lake was formed by the catastrophic collapse of Mount Mazama during a VEI 7 eruption approximately 7,700 years ago. The eruption ejected roughly 50 km³ of magma, emptying the subsurface reservoir and causing the unsupported summit to collapse along ring fractures, creating an 8 × 10 km caldera up to 1,200 m deep. Over the following centuries, the caldera filled with rainwater and snowmelt — there are no inlet or outlet streams — to form the lake. Post-caldera eruptions within a few hundred years of the collapse built Wizard Island and other volcanic features on the caldera floor. The most recent eruption occurred approximately 4,800 years ago.

Is Crater Lake a volcano?

Yes, Crater Lake is a volcanic caldera — a large depression formed by the collapse of a volcano after a massive eruption. The lake occupies the remnant of Mount Mazama, a complex of overlapping stratovolcanoes that was destroyed approximately 7,700 years ago. The Smithsonian Global Volcanism Program classifies it as an active volcanic system, and the USGS considers it dormant rather than extinct. Thermal springs on the lake floor confirm ongoing hydrothermal activity. Post-caldera eruptions occurred as recently as approximately 4,800 years ago, building features like Wizard Island. A future eruption is possible, though it would likely be small and preceded by detectable warning signs.

Why is Crater Lake so blue?

Crater Lake's intense, deep blue color results from two factors: its extreme depth (594 m) and its exceptional water clarity. Because the lake has no inlet streams, it receives almost no sediment, dissolved minerals, or organic matter — only clean rainwater and snowmelt. This means there is very little in the water to scatter or absorb light. Sunlight penetrating the lake is progressively absorbed by wavelength: red, orange, yellow, and green light are absorbed at increasing depths, while blue light penetrates deepest and is scattered back toward the surface. The result is the pure, vivid blue color for which the lake is famous, with Secchi disk transparency readings regularly exceeding 30 m.

Can you swim in Crater Lake?

Swimming is permitted at Crater Lake, but only at the designated area at the base of the Cleetwood Cove Trail — the only legal access point to the lakeshore. The water is extremely cold: summer surface temperatures typically reach only 13–17°C (55–63°F), while deeper water remains near 3°C (38°F) year-round. The steep, 3.3 km (round trip) trail descends 210 m to the shoreline. There are no lifeguards, and the extreme depth means the water drops off sharply. Visitors should exercise caution, particularly given the cold water temperatures that can cause rapid hypothermia.

When was the last eruption at Crater Lake?

The most recent eruption at Crater Lake occurred approximately 4,800 years ago (~2,850 BCE), when a small rhyodacitic lava dome was extruded on the caldera floor east-northeast of Wizard Island. This dome is entirely submerged beneath the lake surface and was discovered during bathymetric surveys. Earlier post-caldera eruptions built Wizard Island and Merriam Cone within a few centuries of the caldera-forming event (~7,700 years ago). The 4,800-year dormancy period is long relative to many Cascade volcanoes but short in geological terms. The USGS classifies the system as dormant with potential for future activity, though any eruption would likely be preceded by weeks to months of seismic and deformation warning signs.

Could Crater Lake erupt again?

Yes, Crater Lake could erupt again. The USGS and Smithsonian classify the volcanic system as dormant rather than extinct. Thermal springs on the caldera floor, detected during 1980s submersible dives, confirm that a heat source persists at depth. A future eruption would most likely involve small-volume lava dome extrusion on the caldera floor or phreatomagmatic explosions caused by magma interacting with lake water. Such an event would likely produce steam explosions, displacement waves within the caldera, and modest tephra fall. A repeat of the catastrophic VEI 7 eruption is considered extremely unlikely in any human-relevant timeframe, as the magma reservoir has not had time to regenerate the enormous volume of magma required.

How big was the Mount Mazama eruption?

The climactic eruption of Mount Mazama approximately 7,700 years ago was a VEI 7 event — one of the largest volcanic eruptions in the last 10,000 years. It ejected roughly 50 km³ of magma (approximately 150 km³ of tephra), comparable to the 1815 Tambora eruption. Pyroclastic flows traveled up to 40 km from the vent, and tephra was deposited over 1,500 km away in central Canada. The eruption was approximately 50 times larger than the 1980 Mount St. Helens event and roughly three times the volume of the 1912 Novarupta eruption. The resulting caldera is 8 × 10 km across and was originally up to 1,200 m deep.

What is Wizard Island?

Wizard Island is a symmetrical cinder cone that rises 230 m (755 ft) above the surface of Crater Lake near its western shore. It was built by volcanic eruptions on the caldera floor within a few centuries of the caldera-forming collapse approximately 7,700 years ago. The cone is topped by a 90-m-wide crater and has a base that extends roughly 500 m below the lake surface to the caldera floor. Wizard Island is accessible to visitors via ranger-led boat tours from Cleetwood Cove (operating late June through mid-September). A steep 2.7 km trail climbs from the island's boat landing to the summit crater. The island was named in 1885 for its resemblance to a sorcerer's pointed hat.

How tall was Mount Mazama before it erupted?

Before its catastrophic eruption approximately 7,700 years ago, Mount Mazama is estimated to have stood approximately 3,400 m (11,200 ft) tall — comparable to the modern height of Mount Rainier (4,392 m) or Mount Shasta (4,322 m), though somewhat shorter. The mountain was a complex of at least five overlapping stratovolcanoes and shield volcanoes that grew over a period from approximately 420,000 to 40,000 years ago. It was heavily glaciated, with valley glaciers extending 15–20 km down its flanks. The eruption removed the entire upper portion of the mountain, and the caldera rim's highest point today stands at only 2,487 m.