No trip to Whistler is complete without a stop at Brandywine Falls. Why? First, because in the summer the traffic jam in the parking lot prepares you for driving back through Vancouver. Second, the falls are beautiful, and they don’t get overcrowded because there is limited parking.
Brandywine Falls are 70 m high and form where Brandywine Creek cascades over a series of stacked lava beds (basalt layers) before it flows into Daisy Lake to the south (1). The continual flow of the creek has formed a bowl-shaped crater that is visually stunning. However, as many of you realize, the beauty of the falls is surpassed by that of the multiple lava flows that form the walls of the bowl.
Geology of Brandywine Falls
The basalt layers visible at Brandywine Falls are the oldest lava flows in a series of events that originated at Mt. Cayley and flowed to the south (2). There is limited age information on the basalts, but they were probably emplaced over less than 2,000 years and between about 10,000 and 40,000 years ago. At the time, the area was covered in thick glacial ice (2), and it is thought that the lava flowed in tunnels beneath the ice following their eruption (2,3). These subglacial flows formed the north-south basalt ridges and valleys that occur in the area (3).
Volcanoes in BC
Mt. Cayley along with Mt. Garibaldi and Mt. Meager are part of the Garibaldi Volcanic Belt (4,5), and the Garibaldi Volcanic Belt is the northernmost extension of a string of volcanoes that includes Mt. Baker, Mt. Hood, and Mt. St. Helens (known as the Cascade Volcanic Arc; 5). These volcanoes form because the Pacific Ocean seafloor is being subducted below North America where it melts. The resulting molten rock (magma) floats upwards, and when it erupts (forms a volcano) it becomes lava and produces the basalt that occurs throughout the Squamish to Pemberton region.
So the next time you are enjoying the view at Brandywine Falls, take a moment to consider the massive movements of the Earth’s surface, the thick ice sheets and the lava flows that came together to produce them!
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Info Sources:
2) Borch, A., Russell, J. K., Barendregt, R. W., and Quane, S. L., 2022, Chapter 3 - Distribution of the Cheakamus Basaltas, Garibaldi Volcanic Belt, British Columbia, in Grasby, S. E., Barendregt, R. W., Borch, A., Calahorrano-DiPatre, A., Chen, Z., Hanneson, C., Harris, M., Quane, S. L., Slobodian, E. G., Unsworth, M. J., Williams-Jones, G., and Yuan, W., eds., Garibaldi Geothermal Energy Project - Phase 2, Mount Cayley 2021 Field Report, Volume Report 2022-14: Vancouver, BC, GeoscienceBC, p. 14-33.
3) Green, N. L., 1977, Multistage andesite genesis in the Garibaldi Lake area, southwestern British Columbia [PhD: University of British Columbia.