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Morphology, volcanism, and mass wasting in Crater Lake, Oregon

Charles R. Bacon, James V. Gardner, Larry A. Mayer, Mark W. Buktenica, Peter Dartnell, David W. Ramsey and Joel E. Robinson
Morphology, volcanism, and mass wasting in Crater Lake, Oregon
Geological Society of America Bulletin (June 2002) 114 (6): 675-692


Crater Lake was surveyed nearly to its shoreline by high-resolution multibeam echo sounding in order to define its geologic history and provide an accurate base map for research and monitoring surveys. The bathymetry and acoustic backscatter reveal the character of landforms and lead to a chronology for the concurrent filling of the lake and volcanism within the ca. 7700 calibrated yr B.P. caldera. The andesitic Wizard Island and central-platform volcanoes are composed of sequences of lava deltas that record former lake levels and demonstrate simultaneous activity at the two vents. Wizard Island eruptions ceased when the lake was approximately 80 m lower than at present. Lava streams from prominent channels on the surface of the central platform descended to feed extensive subaqueous flow fields on the caldera floor. The Wizard Island and central-platform volcanoes, andesitic Merriam Cone, and a newly discovered probable lava flow on the eastern floor of the lake apparently date from within a few hundred years of caldera collapse, whereas a small rhyodacite dome was emplaced on the flank of Wizard Island at ca. 4800 cal. yr B.P. Bedrock outcrops on the submerged caldera walls are shown in detail and, in some cases, can be correlated with exposed geologic units of Mount Mazama. Fragmental debris making up the walls elsewhere consists of narrow talus cones forming a dendritic pattern that leads to fewer, wider ridges downslope. Hummocky topography and scattered blocks up to approximately 280 m long below many of the embayments in the caldera wall mark debris-avalanche deposits that probably formed in single events and commonly are affected by secondary failures. The flat-floored, deep basins contain relatively fine-grained sediment transported from the debris aprons by sheet-flow turbidity currents. Crater Lake apparently filled rapidly (ca. 400-750 yr) until reaching a permeable layer above glaciated lava identified by the new survey in the northeast caldera wall at approximately 1845 m elevation. Thereafter, a gradual, climatically modulated rise in lake level to the present 1883 m produced a series of beaches culminating in a modern wave-cut platform, commonly approximately 40 m wide, where suitable material is present. The new survey reveals landforms that result from intermediate-composition volcanism in rising water, delineates mass wasting and sediment transport into a restricted basin, and yields a more accurate postcaldera history leading to improved assessment of volcanic hazards.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 114
Serial Issue: 6
Title: Morphology, volcanism, and mass wasting in Crater Lake, Oregon
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Pages: 675-692
Published: 200206
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 53
Accession Number: 2002-042997
Categories: GeomorphologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch map
N42°53'60" - N42°58'60", W122°12'00" - W122°00'00"
Secondary Affiliation: University of New Hampshire, USA, United StatesNational Park Service, Crater Lake National Park, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200214
Program Name: USGSOPNon-USGS publications with USGS authors
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