BATHYMETRIC MAPPING OF GLACIO-VOLCANIC LAKES IN GARIBALDI PROVINCIAL PARK, BRITISH COLUMBIA

Garibaldi, Lesser Garibaldi and Barrier Lakes are remote alpine lakes located in the Coast Mountains of Southwestern British Columbia within the confines of Garibaldi Provincial Park, ~20 km south of the Resort Municipality of Whistler. The alpine lakes reside at ~1400 meters elevation and formed by the damming of a paleo valley when a lava flow erupted from Clinker Peak interacted with the retreating Cordilleran ice sheet. The ice-marginal volcanism created a ~300 meter tall dam of unstable volcanic rock called the Barrier behind which glacial melt and seasonal runoff collected to create a system of lakes. Garibaldi Lake is the largest in the system, covering 10 square kilometers with a maximum depth of 255 meters. Lesser Garibaldi Lake and Barrier Lake are two significantly smaller lakes confined within the lava flow. All three lakes straddle the lava flow/bedrock contact. Water levels in the lakes fluctuate significantly throughout the year filling to overflow during spring and summer melt runoff, and draining during snow-laden, runoff free winter months. As Garibaldi Lake overflows, it fills Lesser Garibaldi Lake and as it overflows, it fills Barrier Lake. Barrier Lake only overflows during extreme precipitation events as a waterfall over the shoulder of the Barrier. Concomitantly, Rubble Creek flows at a constant rate of ~3 m³/s from a collection of springs at the base of the Barrier. We hypothesize that Rubble Creek comprises subterranean flow along the porous and permeable bedrock/lava flow contact from all three lakes. Here, we present bathymetric maps of Garibaldi, Lesser Garibaldi and Barrier Lakes. We mapped bathymetry and bottom surface structure of the lakes with side scan sonar; Garibaldi Lake from an inflatable zodiac and Lesser and Barrier Lakes from an inflatable standup paddleboard. By doing so, we elucidate the dynamics of the lava/ice contact formation of the lakes, better refine the lava flow/bedrock contact and determine lake water volume capacity. Combined with ongoing monitoring of seasonal lake levels and overflow rates, we present a quantitative water balance for the Garibaldi Lakes-Barrier-Rubble Creek system allowing us to better assess the behavior of this notoriously unstable volcanic dam.