Old Fort Landslide Update 12 October 2018
Earth flow toe encroaching on island
2012 Pre-slide
8 Oct 2018
10 Oct 2018
10 October Lidar - Old Fort landslides
Rock slide Old slide/flow complex
Previous movement noted in this area between 6 Oct 18 and 7 Oct 18 Earth slide Earth flow
LiDAR Change Detection The next four slides show the difference between Lidar surfaces from different days and years. The following indicates changes in the ground surface: • Blue and green means the surface is lower or has dropped in elevation. • Red and yellow means the surface is higher – or that material has accumulated or bulged. Note that there is always some “noise” (margin of error) in the data, especially in heavily vegetated areas.
LiDAR Change Detection Analysis – 9 Oct 2018 to 2015 Baseline
LiDAR difference 10 Oct 2018 – 2012
LiDAR difference 9 Oct 2018 – 8 October 2018
LiDAR difference 10 Oct 2018 – 9 October 2018
Rubble from disintegrated shale hill Scarp Lateral shear zone of the initial reactivation
Tension cracks noted in the upslope section of the Old Landslide Complex Lateral shear zones of the initial slide
Toe
Bulging
9 Oct 2018 Ortho draped over LiDAR with 2x vertical exaggeration
Western Landslide (below lookout) - about 14 ha, 450 m long as of 10 Oct 2018 - 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 8 Oct 2018 and 10 Oct 2018 - 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 10 Oct 2018 - 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 (outlined in dashed white line) - it has encroached onto the first island in the river 3. Old Landslide Complex - previous movement had been observed between 6 Oct 18 and 7 Oct 18 to 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 of October 10, 2018, movement appeared to be slowing down in the West and Main slides. Please note that landslides are unpredictable and there is potential for these slides to slip and/or speed up again. We will continue to monitor their progress daily, especially for any impact from the precipitation last night and today. Movement has been observed in the northwest section of the old landslide complex area, as per information released previously. The depth and speed of the movement is unknown at this point in time. Further information is being collected. 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. All existing evacuation orders and alerts will remain in place unless otherwise announced by the Peace River Regional District.