In Crater Lake, OR
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Studies ofIi HydrothermaljThcitk iNi ProcessesVL in Crater Lake, OR Robert W. Collier, Jack Dymond and James McManus College of Oceanography Oregon State University Corvallis, OR 97331 In Collaboration With: H. Phinney, D. Mclntire, G. Larson, M. Buktenica Oregon State University R. Bacon, C.'.. H. Nelson, J. H.,. Barber, Jr.ii, U.S.G.S., Menlo Park D KarlTh[ U. Hawaii J. Lupton U.C. Santa Barbara M.'i:i Watwood, C. Dahm U. of New Mexico A. Soutar, R. Weiss U. C. San Diego C. G. Wheat U. of Hawaii Submitted to: TheT National'V' Park Service, PNW Region Seattle, WA May 31, 1991 Cooperative Agreement No. CA 9000-3-0003 Subagreement No. 7 CPSU. College of Forestry, OSUji PATTULLO STUDY COLLEGE OF OCEANIC AND ATMOSPHERIC SCIENCES OSU College of Oceanography Repott # 90- 7 Studies of Hydrothermal Processes in Crater Lake, OR Robert W. Collier, Jack Dymond and James McManus College of Oceanography Oregon State University Corvallis, OR 97331 In Collaboration With: H. Phinney, D. Mclntire, G. Larson, M. Buktenica Oregon State University R. Bacon, C. H. Nelson, J. H. Barber, Jr. U.S.G.S., Menlo Park Karl U. Hawaii J. Lupton U.C. Santa Barbara M. Watwood, C. Dahm U. of New Mexico A. Soutar, R. Weiss U. C. San Diego C. G. Wheat U. of Hawaii Submitted to: The National Park Service, PNW Region Seattle, WA May 31, 1991 Cooperative Agreement No. CA 9000-3-0003 Subagreement No. 7 CPSU, College of Forestry, OSU OSU College of Oceanography Report #90-7 Executive summary Significant Observations 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 lake venting. The mats have internal temperatures which are more than 15 C 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 visible indications of fluid flow through or from the mats, fluid advection is necessary in order to provide the continuous 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 defme 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 °C. Sampling of the mat fluids, the brine pools, and sediment pore waters has dramatically increased the known range of anomalous water compositions within Crater Lake. In the most anomalous fluids manganese is enriched by as much as a million times and222pis enriched 100,000 times over typical lake values. Helium-3, perhaps the most distinctive indicator of a magmatic source, is enriched 500 times over values for waters in equilibrium with the atmosphere. Striking depletions of 14C in pooi fluids and the deep lake waters indicate a magmatic source of "dead carbon" is entering the deep lake. Rare earth element concentrations in lake and sediment pore waters have an abundance pattern which indicate a hydrothermal source. Isotopic compositions of hydrogen in the saline pools clearly show that these anomalous fluids are highly modified lake water and could not have originated outside the lake. The enhanced salt Content of the anomalous fluids enables us to account for the bulk composition of the lake by elucidating the sources of chemical species which were previously unexplained by known water sources such as precipitation and caldera springs. We have identified a third sourcea hydrothermal componentas the major influence on lake composition. Using sensitive analytical methods, we have monitored the active accumulation of heat and salt in the deep lake that results from this source. Various mass balance models indicate that a net heat flow of 15 to 30 megawatts (MW) is carried into the lake by thermal fluids. The calculated flow rates for a thermally and chemically enriched fluid are approximately 200-400 liters/secondroughly two billion gallons per year. Conclusions 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 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 hydrologic 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 the redistribution of dissolved salts and nutrients within the body of the lake. Table of Contents Introduction 1 Methods 3 11.1 General 3 11.2 Bathymetry 5 11.3 Remotely Operated Vehicle (ROV) 5 11.4 Manned-Submersible Operations 7 Navigation 7 Video and Photographic Recording 8 Sampling of Rocks, Crusts, and Sediments 11 Temperature Probe 11 Benthic Barrel 13 Recording Sediment Temperature Probe 13 Interstitial Pore Water Samples - "Peepers" 13 11.5 Water Temperature, Conductivity, and Light Transmission 14 CTD Instrumentation 14 Thermistor Chain Mooring 16 11.6 Current Measurements 16 11.7 Water Samples 17 11.8 Chemical Analyses of Water Samples 17 11.9 Sediment, Crust, and Mat Analyses 20 11.10 Additional Chemical Analyses 21 Results 21 111.1 Major Features Observed With the Submersible 21 hon-rich Crusts 24 Bacterial Mats 24 Pools 24 Spires 40 111.2 Distribution of Temperature, Salt, and Physical Properties 41 General 41 Temperature and Density Structure 41 Deep Lake Distributions 43 Near-Bottom Measurements of Physical Properties 46 Near-Bottom Current Measurements 51 ffl.3 Chemistry of Crater Lake Waters 51 Introduction 51 Distributions of Dissolved Ions With Depth 54 Distribution of CO2 in the Water Column 58 ffl.4 Ion-Ion Systematics 58 111.5 Helium Concentrations and Isotopic Ratios 64 Water Column Samples 64 Submersible Samples 69 Summary - Helium Systematics 69 ffl.6 Dissolved Oxygen 73 Water Column Oxygen and Mixing 73 Oxygen Budget and Influence of Hydrothermal Activity 75 Small-scale Variations in Bottom Water 02 Distribution 78 111.7 Radon-222 81 Estimates of Radon-222 Inventory 83 Radon and Radium in Submersible Samples 86 Radon-222 Constraints on Pool Formation and Exchange Rates 87 Radium-226 Measurements 89 ffl.8 Lakefloor Temperature Data 89 Submersible Temperature Probe 89 Sediment Temperature Profiles 96 111.9 Bacterial Mats 99 1988 Observations 99 Microscopic Evaluations 102 Environmental Settings of the Bacterial Features 104 Chemical Composition of Bacterial Samples 109 Biological and Biochemical Studies 109 111.10 Solid-Phase Geochemistry 111 General 111 Crusts and Mats 112 Spires 118 Pool Sediments 122 Sediment Core Analyses 122 IV.Discussion 125 P1.1 Geological Setting of Features in the Detailed Study Area 125 Regional Setting 125 General Bathymetry 126 Chaski Slide 127 Implication of the Palisades Point Thermal Chemical Features 128 IV.2 Geochemistry of Fluids 129 Composition of Sampled "End-Member" Fluids 129 Geotherinometry 133 Stable Isotope Measurements 136 Rare Earth Elements 142 The Distribution of Dissolved Carbon- 14 147 P1.3 Fluxes of Materials Through the Lake System 154 Mixing Rates of Lakewater 154 Mass Balance of Materials 157 Fluid Flows Through Sediments 168 IV.4 Fluxes of Heat 173 Direct Observations of the Accumulation of Heat 173 Helium-Based Estimates of Heat Flux 174 Ion-Based Estimates of Heat Flux 174 IV.5 Significance of Fluxes on Other Lake Processes 177 Relationship to Other Lake Processes 177 IV.6 Evaluation of Hypotheses 179 Early Fumarolic Input Hypothesis 179 Evaporation Hypothesis 180 The Ash Alteration Hypothesis 181 Volatile Transport Hypothesis 181 The Conductive Heat Hypothesis 183 The Cold Spring Hypothesis 183 The Hydrothermal Hypothesis 185 Summary of Hypothesis Testing 187 V. Summary and Conclusions 189 V.1 Significant Observations 189 V.11 Conclusions 190 VI.References 191 VII.Appendices A The Physical Limnology of Crater Lake, On Mechanisms for the redistribution of heat and salt in the water column A. 1 James McManus, Robert Collier, and Jack Dynwnd B National Geographic Dive Report B. 1 H. Phinney, D. Mclntire, G. Larson, and M. Buktenica C Geological Observations and Sampling C. 1 Charles R. Bacon D Geological Observations and Sampling D. 1 C. Hans Nelson and John H. Barber, Jr. E Bacterial Studies of Materials Collected at Crater Lake Vent Locations