rockslide_seymourriver
Photo by David Webb for North Shore News

Rockslide transforms a river into a new lake on Vancouver’s North Shore

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A rockslide in North Vancouver has transformed an area of canyons and rapids into a brand new lake.

In early December, the rockslide, which contained boulders and debris the size of houses, partially blocked the Seymour River. In only six hours after the initial rockslide, a new lake had already formed where the river once ran. The new lake, which has yet to be officially named, extends 850-meters north from the original slide site and measures six-meters down at its deepest point. In addition to claiming the river, the rock fall has also taken over at least two-hectares of nearby forest, trails, and the Twin Bridges, which is now almost fully submerged.

According to authorities, the new lake isn’t going anywhere.

“The rocks are not moving,” said Mike Mayers, Metro Vancouver’s superintendent of environmental management, in an interview with the North Shore News. “It’s the largest rock fall I’ve heard of on the North Shore in a long time.”

The stability of the new geographic feature also means that local residents near the site of the slide have not been asked to evacuate.

Rocky debris from the slide that formed the new lake in North Shore.
Rocky debris from the slide that formed the new lake in North Shore.
A reference photo of Twin Bridges, which was built in 1098. The water now reaches the blue railings.
A reference photo of Twin Bridges, which was built in 1098. The water now reaches the blue railings.

However Metro Vancouver will be removing Twin Bridges, the historic bridge that connects many of the North Shore’s popular hiking and biking trails. Built in 1908, the concrete and steel bridge will be removed for public safety.

“We think it is a threat to the river and certainly to the public,” said Bob Cavill, Metro Vancouver’s watershed manager, to The Province. “It is not a functional bridge and it is a trap for debris. We feel that bridge should be taken out.”

Metro Vancouver plans to rebuild the trails destroyed by the slide—an idea that already has the local mountain biking association excited.

Geotechnical engineers monitoring the site believe a process called “ice-jacking” caused the rockslide. Ice-jacking occurs when water gets inside a confined space—in this case, behind the boulders of the rock face overlooking Seymour River—and freezes and thaws over a period of time. This process slowly eroded the rock face, which eventually broke off and tumbled into the river.

Since the rockslide, the area has become a tourist attraction among geography buffs, families and outdoor enthusiasts. Now, all the lake needs is an official name.

“Personally, I’m more about the features that created it. At the north end of it, Boulder Creek flows right into it and a big boulder feel down and created it. I’d go with that really imaginative name—Boulder Lake,” Mayers said.