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.

Last updated: September 8, 2023

Park footer

Contact Info

Mailing Address:

Crater Lake National Park
PO Box 7

Crater Lake, OR 97604


541 594-3000

Contact Us