Detailed field data on the occurrence, flow pattern, and internal dynamics of both surge and continuous turbidity currents have been obtained with a three-dimensional array of optical and thermal sensors. The array, operated in a glacial lake in southeastern British Columbia, collected detailed information on the character of surge events with velocities reaching 110 centimeters per second and continuous underflows exceeding 90 centimeters per second. Thefindings (i) indicate that such currents are frequent events, occurring with density differences between the incoming stream water and the lake water as low as 0.19 kilogram per cubic meter of water; (ii) document the differences in the initiation and internal characteristics of the continuous and surge events; and (iii) support the concept of erosion by turbidity currents.