Keyhole Falls

Keyhole Falls is the largest waterfall along the Lillooet River (perhaps the only significant waterfall along the Lillooet River) and is one of the most significant waterfalls in southern British Columbia by volume. The falls were formed as the river carved through a thick bed of lava which was deposited in the valley by an eruption from the neighboring Mount Meager volcanic group, one of three volcanic complexes associated with the Cascades Volcanic Arc found in British Columbia. The lava flow completely blocked the path of the Lillooet River, and over time the silt in the river back filled the valley upstream of the lava dam and brought the river to a level elevation with the top of the flow. Over thousands of years it carved into the lava flow and eventually formed a narrow slot canyon which has thus far carved about two-thirds of the way through the lava flow. As it exits the canyon, it plunges over Keyhole Falls, dropping approximately 35 meters (120 feet) into a much broader bowl-shaped canyon below. The cliffs lining the headwall where the falls emerge from the narrow canyon rise nearly 100 meters straight out of the river. It appears there may be two more falls located within the depths of Keyhole Canyon itself, however as the slopes along the rim of the canyon are unstable, and the canyon is so narrow, there doesn't appear to be a sane way to look into its depths to see what may be there. In 2017 a dam located just upstream from the beginning of the Keyhole Falls Canyon came online and began to divert a majority of the volume of the Lillooet River into a new hydroelectric system which bypasses the falls entirely, resulting in a greatly reduced flow of water going over the falls. Because the Lillooet River is quite large, the flow will still be significant in the spring and potentially summer months when the glaciers upstream are melting at their fastest, but the full natural flow of the river will not likely ever be seen flowing over the falls until and unless the diversion is shut down or at least temporarily disabled for maintenance. The Lillooet River upstream of Keyhole Falls drains from an area covering approximately 540 square kilometers (210 square miles), and is largely sourced by the Lillooet, Manatee, Job, Mosaic, and Dalgleish Glaciers, as well as dozens of smaller unnamed glaciers. The average volume of water present in the Lillooet River at the falls is not known, but its natural volume (excluding the diversion) during the spring and summer months is thought to be at least 80-100 cubic meters per second. The diversion for the hydro project is capable of siphoning off as much as 53 cubic meters per second, and given the substantial flow rates which were observed during our survey in May 2018, it seems likely that the river regularly reaches volumes in excess of 100 cubic meters per second, if not considerably more. There is unfortunately no developed access to clear views of Keyhole Falls. A rough trail leads from a nearby road to the rim of the canyon directly above the falls, but because the cliff is significantly undercut, one cannot see the falls by staring down into the canyon from the top of the cliff. When we attempted to survey the site in May of 2018 we were only able to obtain photographs of the falls using a drone, and we were not able to take measurements of the falls in turn. It is possible to get close to the falls by hiking up the canyon from the Keyhole Hot Springs trail, however as of summer 2018 the trail had been closed indefinitely due to frequent visits by habituated grizzly bears.