The first known self-draining of Summit Lake occurred in December 1961, followed by similar events in November 1965, September 1967, and November 1968. It has been noted that the rate of draining increases rapidly until the lake is empty (Mathews 1969). In August 1967 it was also noted that the runoff per unit area from the basin of Summit Lake, based on the rate of water volume change in the lake and overflow from the lake, was approximately one half the runoff per unit area from a glacierized basin to the north. It was suspected that at least part of this difference was due to leakage through the ice dam. More detailed observations made in July and August 1968 of the water balance of the lake basin indicate that, in August, there probably existed a leak possibly as large as 3 to 5 m³ sec ̄¹ . The tracing of lake water with fluorescent dye on three occasions also indicated the existence of a leak. Records of lake temperature from surface to bottom were kept from July through September with the results that: a) the warmest water was found at the bottom, and the coldest at approximately one third depth in most cases, b) the warmest temperatures occurred in the north end of the lake in early July; water temperatures decreased southward toward the ice dam and at all locations through the summer, and c) a mean water temperature of approximately 1°C is estimated for July decreasing to 0.7°C by September. For the 1965 draining a lake water temperature of 0.2°C is sufficient with the heat generated due to loss of potential energy to account for the enlargement of the tunnel in the terminal stages of draining, whereas a water temperature of 0.9°C is required for the 1967 flood. No evidence of sudden density overturn of the lake water could be found either from the temperature measurements or the results of dye tracing in the lake water in 1969. Water temperature records on three streams flowing into the lake indicate that from the entire drainage basin approximately 320 x 10¹º calories per day of heat may have been advected to the lake in August 1968. / Arts, Faculty of / Geography, Department of / Graduate