MIXING PROCESSES IN CRATER LAKE, OREGON

Subsurface hydrothermal activity dominates the heat and salt budgets o f the deep water column in Crater Lake, Oregon. From a time series of conductivity-temperature-depth data and data from a thermistor chain m ooring, we estimate that the net hydrothermal heat flow is approximate ly 1 W m-2 and the corresponding salt flux is approximately 5 mug m-2 s-1. This paper discusses the observation of these fluxes and the mech anisms and time scales of mixing responsible for the redistribution of these properties through the water column. Free convection and wind m ixing homogenize the upper 200 m of the like twice annually. Deep-lake ventilation occurs during early winter and to some extent during late spring. However, since the deep lake does not reach atmospheric satur ation with respect to dissolved oxygen at any time during the year, ve ntilation of the deep water appears to be incomplete. During periods o f seasonal stratification, the active input of hydrothermally enriched fluids, produces heterogeneities and instabilities in the density str ucture of the deep lake that may drive deep-lake mixing. As a result o f these and other mixing processes, Crater Lake remains relatively wel l mixed, despite its great depth.