A brief history of landslides, debris torrents and their causes
The devastating landslide that took the lives of Barbara and David Enns on December 14 is just the latest in a long line of deadly events plaguing the geotechnically hazardous Sea to Sky region.
A report on landslide hazards and mitigation along the Sea to Sky corridor by Dr. Andrée Blais-Stevens in 2007 identified 154 reported landslide events that have occurred in the region since the late 1800s, and there have been several deadly events since.
In this second part to our series examining the impact of geohazards in and around Lions Bay, we take a closer look at the most significant of these events.
Though there have been cottages at Brunswick Beach since 1911, the first homes in Lions Bay began to go up in the 1960s, and the Village was incorporated in 1971.
According to the Cordilleran Report commissioned by Council in 2017, this was before any real standards for landslide hazard risk management were established in BC. So while homes in the Village continue to be built to the existing standards, these have changed over time.
In general, landslides are divided into six distinct types: rock fall, rock avalanche, rock slide, debris slide, debris flow, and submarine landslide.
Unlike rockfalls or avalanches, debris flows generally channel their load of saturated trees, rocks and soil along an existing water route.
A map (right) of the more than 150 events in the past century and a half, shows that the most common in the Sea to Sky corridor are rock falls and debris flows, and the majority of these have occurred between West Vancouver and Porteau Cove.
"It is important to note that in the southern part of the corridor, the highway is just metres away from very steep bedrock slopes unlike in the northern part of the highway where the valley is wider," Blais-Stevens wrote in her report.
This report was written during the substantial reconstruction of the Sea to Sky highway prior to the 2010 Olympic Games.
Reported events increased dramatically in the 1950s, likely as a result of the construction of the rail line between Horseshoe Bay and Squamish. Another flurry of incidents occurred in the 1980s and '90s as development increased along the corridor, bringing more people and infrastructure construction.
In the 25 years it took to complete construction of the rail line and highway along the Sea to Sky from 1958 to 1983, 14 debris torrents took place along six creeks, resulting in 12 deaths and the destruction of 11 bridges and four houses. This includes the torrent that roared down Alberta Creek through Lions Bay in February of 1983, killing 19-year-old David Wade and his younger brother Tom.
Other notable events include:
1915: In Canada's second-most deadly slide (after the Frank slide in Alberta) 200,000 cubic metres of rock fell onto the Jane Camp at Britannia Beach, killing 56 people.
1921: Six years later, a debris torrent along Britannia Creek caused by the collapse of a culvert, destroyed 60 houses and killed 37 people.
1981: A debris torrent that began on the margin of an old clear-cut high above the Sea to Sky highway took out the bridge at M Creek. The timber trestle bridge was swept away in less than 30 seconds. Five cars drove into the abyss in the darkness that night before the highway was closed. Nine people died in total.
1982: On a cold January day, traffic came to a halt at Brunswick Point due to heavy snowfall. While the vehicles were stopped, a boulder fell from above and landed on a car. The 28-year-old woman driver was killed and her father in the passenger seat was injured.
1983: As noted above, on February 11, a debris torrent on Alberta Creek killed the Wade boys and destroyed three houses and much infrastructure in Lions Bay.
1990: 10,000 cubic metres of rock fell at Logger's Creek, blocking the highway for 12 days and costing about $7 million to clean up.
2021: A slide of mud, trees and water thundered down the slope above Duffey Lake Road (the stretch of Highway 99 between Pemberton and Lillooet) sweeping away cars and people. Five people died, including 36-year-old Brett Diederichs, whose body has never been found.
In the wake of these tragedies, many questions about what caused these events and how they can be prevented – or at least mitigated – remain. In the next installment, The Watershed will examine who is responsible for geohazard mitigation, what legislation currently exists and the gaps in both. We'll also take a look at the changes that experts are calling for, as well as what residents of the Sea to Sky region can do to help keep themselves safe.
This is the second in a series of articles with the goal of increasing geohazard awareness
in the Sea to Sky region. The first article can be found HERE.
Share your thoughts below, or email
Please consider supporting local independent journalism
by subscribing HERE.
