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Hydrothermal fluid circulation through the sediment of Crater Lake, Oregon: Pore water and heat flow constraints Public Deposited

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  • We present evidence for pore water flow through the sediment of Crater Lake, Oregon based on systematic variations in pore water chemical compositions and thermal gradients. Pore water was extracted from sediment by centrifugation and diffusive exchange using a gravity corer deployed from a surface vessel and a box corer and peepers deployed from the submersible Deep Rover in a known geologic context. Depth profiles of sediment temperature were measured using two probes deployed from the submersible. One probe was connected to the submersible whereas the other was self‐contained and deployed for 7 days. On the basis of measured and calculated depth profiles of pore water Na, Ca, Mg, K, Li, and temperature, we show that pore water upwells in zones of focused upflow at speeds of meters to hundreds of meters per year. These zones of focused flow are patchy and usually cover several square meters to hundreds of square meters and are marked by iron‐manganese‐rich crusts, bacterial mats, and saline pools. In contrast, most of the lake floor consists of sediment derived from the caldera walls and has a low heat flow with pore water velocities of millimeters per year. The chemical composition of the pore water that upwells through the sampled section of the sediment column differs from core to core. This difference results from mixing a hydrothermal fluid in igneous basement below the lake with lake water before the final ascent through the sediment column. Elemental ratios of this thermally and chemically altered fluid in basement match those calculated based on mass balance considerations. Calculation of mass balance and geothermometry constrain the temperature in basement and ultimately the power output, which is about 30 MW. This power output is in agreement with two other estimates that were calculated using temperature data from the water column and measurements of sediment heat flow.
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  • Wheat, C., J. McManus, J. Dymond, R. Collier, and M. Whiticar (1998), Hydrothermal fluid circulation through the sediment of Crater Lake, Oregon: Pore water and heat flow constraints, J. Geophys. Res., 103(B5), 9931-9944. doi: 10.1029/97JB03391
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  • 103
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