BATHYMETRY AND DYNAMICS OF GARIBALDI LAKE, B.C

Garibaldi Lake, a picturesque alpine lake located in Garibaldi Provincial Park, British Columbia exists due to a series of seemingly conspiratorial geologic events that occurred approximately 11,000 years ago. During this time, the Cordilleran ice sheet was in rapid retreat, filling valleys in the area from sea level to ~1220 metres above sea level (m.a.s.l). In contrast, local mountain glaciers were stable only at relatively high elevations (~1500 m.a.s.l). In this spatially and temporally limited, mid-elevation, ice free window (~1220 to 1500 m.a.s.l.), Clinker Peak (a part of the Garibaldi Volcanic Complex) erupted and a lava flow began its predictable down-valley journey. With valley ice acting as a dam, the flow arrested, over-thickened and solidified. Subsequent melting of the valley filling glaciers left a 250 m high, unstable cliff called the Barrier. The Barrier effectively dammed surface water outflow from the surrounding watershed and drowned the pre-existing mountain valley to a maximum depth of nearly 260 m, and created Garibaldi Lake. Currently, lake water drains from beneath the Barrier at between 2 and 4 cubic meters per second via a series of springs into Rubble Creek. To elucidate details regarding the formation and dynamics of this fascinating system we mapped the bathymetry of the lake bottom using dual frequency single beam sonar and resolved primary lava flow textures beneath the lake surface via dual frequency and 3D interferometric side scan sonar. From these images, we mapped the paleo topography of the valley prior to Garibaldi Lake’s existence and can reconstruct the timing of volcanic and glacial events leading to its formation. Furthermore, we set up three water level monitoring stations for the lake level, overflow level and Rubble Creek to create a “water budget”. Results indicate that lake level of the ~1 billion m³ lake changes several meters seasonally; filling to overflow during summer run off and draining, via Rubble Creek, along the lava flow-bedrock contact during winter freeze up. Here, we combine results from surface and bathymetric mapping and hydrologic monitoring to predict seasonal and long term behavior of the lake leading to a better understanding of potential hazards from this hydro-dynamic system.