The Barrier

The Barrier
The Barrier is a rock wall formation caused by the damming of lava flows following a volcanic eruption from Clinker Peak on Mt. Price about 12,000 years ago. Lava flowed into the Cheakamus River valley and was stopped by the Cordilleran Ice Sheet, resulting in the formation of a lava dam that we now know as the 250 meter high cliff called the Barrier. The Barrier effectively dammed surface water outflow from the surrounding watershed, and created Garibaldi Lake, Lesser Garibaldi Lake, and Barrier Lake. Water from these lakes seeps from beneath the Barrier via a series of springs into Rubble Creek.

Historical Events and Hazard Overview
Several major landslides and debris flows have occurred on the Barrier since its formation thousands of years ago. These are the main risks associated with the Barrier as rockfall and landslide debris has the potential to block Rubble Creek and cause outburst debris flooding further down on the Cheakamus River. The most recent major landslide on the Barrier in 1855 formed a large boulder field, which gives Rubble Creek its name. In 1981, concerns about additional catastrophic landslides prompted the Provincial government to declare the area immediately below the Barrier unsafe for human habitation, which led to the relocation of residents in the small resort village of Garibaldi to areas away from the hazard zone. Although unlikely to occur, debris flows could affect critical infrastructure near Rubble Creek like Highway 99, and outburst flooding on the Cheakamus could have limited consequences within the District boundary.

Living with the Hazard
The Barrier is considered a physically unmitigable hazard that is instead managed through land use policy, monitoring, and research. Hydrologic floods, earthquakes, and wildfires pose risks that are orders of magnitude higher in terms of likelihood and consequences for Squamish, which is why the District concentrates mitigation efforts and resources on managing these hazards.

Ongoing Research:
The Barrier continues to be studied by a number of academic institutions. Quest University researchers mapped the bathymetry of Garibaldi Lake, Lesser Garibaldi Lake, and Barrier Lake between 2016 and 2018 to better understand the relationship between lake water levels, the lava dam, and Rubble Creek. The volume of water was also more accurately measured in each of these lakes, as well as scanning for drainage points. Researchers from the University of British Columbia have also been conducting terrestrial laser scans of the Barrier since 2017 to determine rockfall rates and detect changes in the surface of the Barrier over time. UBC’s monitoring has shown that although rockfalls occur fairly regularly, the majority of rockfalls are very small: 91% of rockfalls have a volume ≤ 0.1 m3, and only 2% of rockfalls have a volume > 1 m3. Simon Fraser University’s Centre for Natural Hazards Research has also placed monitoring equipment throughout the Sea to Sky region to measure seismic and gravitational shifts that may have an impact on geo-hazards like landslides and rockfalls.

See the final IFHMP report for details.