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Surveys show extent of Old Fort landslide

The Old Fort landslide appears to have slowed down, but that doesn't mean it won't speed up again, say geologists studying the kilometre-long chunk of earth making its way into the Peace River. The slide began Sept. 30 and movement began slowing Oct.
oldfortlandslide
Old Fort landslides, Oct. 20 LiDAR survey.

The Old Fort landslide appears to have slowed down, but that doesn't mean it won't speed up again, say geologists studying the kilometre-long chunk of earth making its way into the Peace River.

The slide began Sept. 30 and movement began slowing Oct. 10, according to Westrek Geotechnical Services, hired by the Peace River Regional District to monitor the landslide. 

"Please note that landslides are unpredictable and there is potential for these slides to slip and/or speed up again," the company noted in an Oct. 12 report.

"We will continue to monitor their progress daily, especially for any impact from the precipitation last night and today."

The landslide has grown to a combined eight million cubic metres covering 39 hectares.

The landslide is being monitored in three sections. From Westrek's report:

1. Western Landslide (below Peace River lookout)

  • about 14 ha, 450 m long as of Oct. 10

  • translational landslide (much is being “rafted” along with minimal surficial disturbance including an intact sewage lagoon)

  • displacement less than 20 m in horizontal direction between Oct. 8 and 10

  • deep cracks up to 6 m depth within the rafted section

2. Main Landslide

  • about 25 ha, this is the longest one (1.3 km) as of Oct. 10

  • varies between 100 and 200 m in width

  • rock slide (upper zone) that triggered an earth flow

  • note the secondary earth flow starting from below the road

  • it has encroached onto the first island in the river

3. Old Landslide Complex

  • previous movement had been observed between Oct. 6 and 7 in the upper northwest corner near the gravel pit. This area is being monitored for additional movement: length, width, and offset in the cracks observed.

"As more LiDAR data and other information and observations become available, our team of experts will work to refine the analysis and provide further update on the size and overall movement of the slide
areas," the company wrote.

All existing evacuation orders and alerts remain in place.

Read the report by clicking here, and scroll below for photos: