CRATER LAKE REVEALED

By

David W. Ramsey, Peter Dartnell, Charles R. Bacon, Joel E. Robinson, and James V. Gardner

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sed sediment gravityflow deposits

talus and debrisflow deposits

landslide and debrisavalanche deposits

andesite & dacite 

of Mount Mazama

pre-Mazama rocks,

undivided

rhyodacite lava & 

breccia

andesite of Wizard

Island, lava & breccia

andesite of Merriam 

Cone, lava & breccia

andesite of the central 

platform, lava & breccia

andesite of the east basin

Around 500,000 people each year visit Crater Lake National Park in the Cascade 

Range of southern Oregon. Volcanic peaks, evergreen forests, and Crater Lake s 

incredibly blue water are the park s main attractions. Crater Lake partially fills the 

caldera that formed approximately 7,700 years ago by the eruption and subsequent 

collapse of a 12,000-foot volcano called Mount Mazama. The caldera-forming or 

climactic eruption of Mount Mazama drastically changed the landscape all around 

the volcano and spread a blanket of volcanic ash at least as far away as southern 

Canada.

Prior to the climactic event, Mount Mazama had a 400,000 year history of cone 

building activity like that of other Cascade volcanoes such as Mount Shasta. Since 

the climactic eruption, there have been several less violent, smaller postcaldera 

eruptions within the caldera itself. However, relatively little was known about the 

specifics of these eruptions because their products were obscured beneath Crater 

Lake s surface. As the Crater Lake region is still potentially volcanically active, 

understanding past eruptive events is important to understanding future eruptions, 

which could threaten facilities and people at Crater Lake National Park and the 

major transportation corridor east of the Cascades.

Recently, the lake bottom was mapped with a high-resolution multibeam echo 

sounder. The new bathymetric survey provides a 2m/pixel view of the lake floor from 

its deepest basins virtually to the shoreline. Using Geographic Information Systems 

(GIS) applications, the bathymetry data can be visualized and analyzed to shed light 

on the geology, geomorphology, and geologic history of Crater Lake.

U.S. Department of the Interior

U.S. Geological Survey

Geologic Investigations Series I-2790

2003

Crater Lake, Oregon

0 1 2 3 4 km

122¡05’W

42¡54’N

122¡10’W

42¡58’N

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Chaski Bay

Danger

Bay

Cloudcap Bay

Grotto

Cove

Roundtop

Cleetwood

Llao Cove

Rock

Llao

Bay

Steel Bay

Northwest

basin

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erria m

Co ne

East

basin

Palisade

Point

Skell

Head

Sentinel

Rock

Kerr

Notch

Sun

Notch

Phantom

Ship Eagle

Point

Southwest

basin

Wizard

Island

central

platform

d o m e

rhyodacite

Watchman

The

Generalized geologic map of the floor of Crater Lake, Oregon.

Upper image: Panoramic photograph taken from

visitor overlook on The Watchman by Peter Dartnell.

View is to the east. Digital photographic processing

by Eleanore Ramsey.

Lower image: Digital perspective view of generalized

geologic map of the lake floor draped over shadedrelief image of 2-m bathymetry. Illuminated from 225

azimuth and 45 elevation. Created with ArcInfo and

USGS perspective view calculation program. Scale

varies with distance.

Oregon

Crater Lake

Location Map

photo by Charles R. Bacon

Selected References:

Bacon, C. R., Gardner, J. V., Mayer, L. V., Buktenica, M. W., Dartnell, Peter, Ramsey, D. W., and 

Robinson, J. E., 2002, Morphology, volcanism, and mass wasting in Crater Lake, Oregon: 

Geological Society of America Bulletin, v. 114, p. 675-692.

Gardner, J. V., Dartnell, Peter, Hellequin, Laurent, Bacon, C. R., Mayer, L. A., Buktenica, M. W., 

and Stone, J. C., 2001, Bathymetry and selected perspective views of Crater Lake, OR: 

U.S. Geological Survey Water Resources Investigations Report 01-4046, 2 plates, scale 

1:15,000, http://walrus.wr.usgs.gov/pacmaps

Gardner, J. V., and Dartnell, Peter, 2001, 2000 multibeam sonar survey of Crater Lake, Oregon; 

Data, GIS, images, and movies: U.S. Geological Survey Digital Data Series DDS-72, 

http://geopubs.wr.usgs.gov/dds/dds-72

Klimasauskas, Ed, Bacon, C. R., and Alexander, Jim, 2002, Mount Mazama and Crater Lake; 

Growth and destruction of a Cascade volcano: U.S. Geological Survey Fact Sheet 92-02,

4 p., http://geopubs.wr.usgs.gov/fact-sheet/fs092-02

Nelson, C. H., Bacon, C. R., Robinson, S. W., Adam, D. P., Bradbury, J. P., Barber, J. H., Jr., 

Schwartz, Deborah, and Vagenas, Ginger, 1994, The volcanic, sedimentologic, and 

paleolimnologic history of the Crater Lake caldera floor, Oregon; Evidence for small caldera 

evolution: Geological Society of America Bulletin, v. 106, p. 684-704.

Prepared in cooperation with the

National Park Service

For sale by U.S. Geological Survey, Information Services, Box 25286,

Federal Center, Denver, CO 80225 or call 1-888-ASK-USGS

Available on World Wide Web at http://geopubs.wr.usgs.gov/i-map/i2790 Wizard Island cinder cone is flanked by forested partially drowned

lava flows erupted while Crater Lake was filling.

Phantom Ship is a remnant of resistant lava within the oldest part of

Mount Mazama above lake level.

Talus rests on the bench known as Chaski slide, a landslide block

photo by Charles R. Bacon arrested in its descent into Chaski Bay. photo by Charles R. Bacon