THE LAKES IN NEWBERRY CALDERA

This poster presents revised bathymetric maps of Paulina and East Lakes located in the summit caldera of Newberry volcano, central Oregon. The maps are constructed from real-time differentially corrected GPS data coupled with sonar data that was collected during the spring and early summer of 2001. In addition, reconnaissance geologic overlays of the lake’s basins are included. These overlays are derived from coring, dredging and scuba observations conducted between 1996 and 2001. The bathymetric maps and overlays reveal several submerged geologic features including a paleo-shoreline in Paulina lake (and possibly at East Lake), multiple tephra layers, rhyodacite domes, and thermal springs. The paleo-shoreline in Paulina Lake is tentatively dated at 6750 +/- 350 radiocarbon yr. Tephras thus far identified include the ash flow of Paulina Lake and the Mazama tephra. Thermal springs have been observed and sampled at the bottom of both lakes to depths of 10 m. Water quality data for Paulina lake covers a temporal span of two years (5/200 – 5/2002). The data describe the annual thermal stratification of the lake beginning with isothermal conditions from winter through early spring followed by the development of a pronounced summer metalimnion that separates a relatively warm (12-18 oC), 10m thick epilimnion from a cold (4 oC) hypolimnion. Coincident with the metalimnion is a pronounced dissolved oxygen maximum (14-18 mg/L) situated near the base of the metalimnion. A small set of water quality data obtained from East Lake during the summer of 2001 is compared with corresponding data from Paulina Lake. Coupled with bathymetric data, the water quality measurements suggest that the two lakes have different mixing characteristics, with Paulina Lake experiencing more complete mixing. Long-term sampling and water quality monitoring are planned and should provide additional insight into the geology and hydrology of the summit caldera and associated volcanic lakes at Newberry.