NEWS

Water-logged slope possible cause of B.C. landslide

07/13/2012 10:24 EDT | Updated 09/12/2012 05:12 EDT
Engineers are trying to determine just what caused Thursday’s devastating landslide at Johnsons Landing, B.C., which some suspect was related to heavy spring rains and an unstable slope.

While search crews focused their attention Friday on rescuing any potential survivors, geological engineers were looking at aerial photos of the steep slope above Johnsons Landing to find any indications of a changing landscape.

One area on the slope stands out to Vancouver engineer Frank Baumann.

"I looked at the 2003 government air photos and it’s very clear that this starting zone... where this slide started, is really very obvious on those air photos,” Baumann said.

“In other words there was a large area of unstable ground that's been there since at least 2003."

Baumann said there are three ingredients that make up a slide: a steep slope, loose material, and water.

There was no shortage of moisture on that slope this year, said CBC meteorologist Claire Martin

The snow pack in, that area especially, was really high. It’s taken a long time to melt, and we’ve seen rapid melt recently,” Martin said. “Not only that, we got some pretty heavy spring rains.”

A similar landslide took place in 1990, near the community of Joe Rich, B.C., about 120 kilometres due west and in similar country to Johnsons Landing.

Houses were destroyed and three people were killed. That slide was blamed on debris flows triggered by heavy rains.

"If we do have suspect ground [in Johnsons Landing], then the most important thing is to get on the ground there and walk the ground, and look for signs of failure, such as tension cracks, or trees that are bent, re-curved trees,” said Baumann. “When a slope slowly moves, the trees tend to get bent out of shape.”

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