Investigator’s Annual Reports (IAR’s) for Crater Lake National Park

Studies of hydrothermal processes in Crater Lake, Oregon

 

Report Number: 12709

Reporting Year: 1991

Permit Number: CRLA1991AADR

Current Status: Checked in

Date Received: Jan 01, 1998

Principal Investigator: Jack Dymond, Oregon State University, College of Oceanography, Corvallis, OR

Park-assigned Study Id. # CRLA1991AADR

Permit Expiration Date: Jan 01, 1998

Permit Start Date: Jan 01, 1998

Study Starting Date: Jan 01, 1987

Study Ending Date: Jan 01, 1991

Study Status: Completed

Activity Type: Other

Subject/Discipline: Other

Objectives: To evaluate possible hydrothermal sources to Crater Lake. The research, which is part of a 10-year Limnological Study of Crater Lake, is designed to: (1) define the thermal and chemical variability in the deep lake, (2) examine the data for evidence of a hydrothermal source, (3) design and carry out a program that would find possible venting sites and sample any associated fluids, and (4) evaluate alternative mechanisms to explain the observed thermal and chemical variability.

Findings and Status:  Measurements of temperature and salt content within the South Basin of Crater lake show surprising variations over distances of a few meters. These thermal and salinity gradients can only be maintained by a continuing input of anomalous fluids.;Communities of bacteria, which produce impressive mat features on rock outcrops and sediment surfaces, mark sites of deep water venting. The mats have internal temperatures which are more than 15 degrees higher than lake bottom water. These communities apparently use the abundant reduced iron in the advecting fluids to fuel their metabolism. Although there were no visble indications of fluid flow through or from the mats, fluid advection is necessary to provide the continous input of reduced chemical species which is required for the survival of these prolific bacterial communities. The temperature gradients within the mats indicate that the advection rates are as high as 100 meters per year. Consequently, the bacterial mats are visual markers of thermally and chemically enriched fluid venting.;Pools of saline water, with major element contents that are approximately ten times greater than background lake values, have been discovered in two widely separated areas of the lake. Sediment pore water compositions from some South Basin cores are similar to those of the pools. The pore water measurements define non-linear gradients which indicate vertical fluid advection rates of up to two meters/year. These measurements as well as the major element compositions suggest that the fluids advecting through the sediments, the brine pools and the bacterial mats are derived from a similar source. Results from chemical geothermometry determinations suggest that this source equilibrated with silicate rocks at temperatures ranging from 40 to 165 degrees celsius.;In conclusion, as a result of the past three years of field studies and our interpretation of these and other data from the literature, we conclude that there are inputs of hydrothermal fluids into the bottom of Crater Lake. The dissolved materials associated with these thermally and chemically enriched fluids, coupled with the overall hydrolic balance, control the observed chemical composition of the lake. Because the hydrothermal input dominates the flux of most dissolved chemicals into Crater Lake, the hydrothermal process is highly significant. Furthermore, the geothermal inputs have a direct effect on the density structure of the deep lake, and therefore can profoundly affect the rate of heat transport and redistribution of dissolved salts and nutrients within the body of the lake.

For this study, were one or more specimens collected and removed from the park but not destroyed during analyses? No

Funding provided this reporting year by NPS: 48116

Funding provided this reporting year by other sources: 0

Full name of college or university:  n/a

Annual funding provided by NPS to university or college this reporting year: 0

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