Sedimentation in Chilko Lake: a record of the geomorphic environment of the eastern Coast Mountains of British Columbia, Canada

Chilko Lake is the largest and deepest lake draining the Coast Mountains of British Columbia. A sedimentary record from the 60-km long lake was constructed by using 3.5-kHz subbottom acoustic profiles and short cores of surface sediments. Sediment accumulation since deglaciation is remarkably thin, averaging less than 10 m, except in the central deep part of the lake, despite extensive activity of Holocene and modern glaciers in the 1960-km 2 contributing watershed. Sediment focusing of silts and clays in the main part of the lake occurs mainly by overflow/interflow processes from the Edmond and Nine Mile/Deschamps drainages. Sandy turbidites from these drainages and other smaller streams, however, extend for several kilometers into the lake basin. Distinct laminae in short cores from the central lake suggest that modern rates of deposition reach a maximum of 2.2 mm a −1. 210 Pb dating and inferences from the acoustic results, however, indicate a lake-wide, long-term average rate of less than 1 mm a −1, which is equivalent to a specific sediment yield of about 80 t km −2 a −1. This specific yield is amongst the lowest for glacier-fed lakes of the southern Canadian Cordillera. A low sediment supply can be related to three factors: (1) a much drier climate on the leeward side of the Coast Mountains producing lower specific discharges; (2) fewer autumn rainstorms that affect mainly lakes west of the Coast Mountains and (3) opportunities for storage of sediment in the lower 20 km of Edmond River, which drains the most heavily glacierized portion of the watershed.