High-energy sedimentary processes in Kluane Lake, Yukon Territory
glacilacustrine sedimentation , turbidity currents
A lacustrine sedimentary process study was undertaken at Kluane Lake, which is a large, glacier-fed, alpine lake in the southwestern corner of Yukon Territory. Data from moored instruments, sediment traps, water column profiling, and high-resolution sub-bottom acoustic surveys were collected over the peak melt seasons of 2006 and 2007 in order to document the spatial and temporal lacustrine sedimentation patterns. A river monitoring station was also established to continuously record the inflow variations of Slims River, which drains meltwater from Kaskawulsh Glacier. Kluane Lake receives sediment-laden (up to 5 g/l) water from Slims River, which varies diurnally in terms of both discharge and suspended sediment concentration. While evidence of seasonal sediment exhaustion is present within the system, the diurnal hysteresis relationship between discharge and suspended sediment is either insignificant or more commonly counterclockwise. The high suspended sediment load delivered by Slims River produces continuous, diurnally fluctuating turbidity currents with maximum velocities in excess of 0.6 m/s at delta-proximal locations, although velocities between 0.2 and 0.4 m/s are more typical. During peak flow conditions, variations in current velocity can be traced to the deepest portion of the lake, over 4 km from the point of inflow. The longitudinal changes in the vertical concentration profiles, suspended sediment load, and mass accumulation rates suggest that the flow structure of the turbidity currents changes rapidly along the first several kilometres of flow. Sedimentation in the Kluane Lake basin is dominated by turbidity currents; overflows occur intermittently and contribute less than 2% to sediment accumulation along the lake bed. The highest rate of deposition occurs approximately 1 km from the delta and is consistent with an accumulation of approximately 0.4 m/a; closer to the delta, high current velocities appear to inhibit sediment deposition. The sediment in Kluane Lake is dominated by silt-size particles and contains virtually no sand except in small amounts very close to the delta. The diurnal pattern of turbidity current activity produces daily rhythmites in sediment traps deployed near the lake bottom, but these laminations do not occur consistently over time or space.