Onsite visit leads to Ledgewood-Bonair landslide quick report
OLYMPIA – The Washington State Department of Natural Resources Division of Geology & Earth Resources has released their quick report on the Whidbey Island “Ledgewood-Bonair” landslide that occurred March 27, 2013.
View the full report: http://www.dnr.wa.gov/publications/ger_qr_whidbey_island_landslide_2013.pdf
Key points from the report include:
- The Ledgewood-Bonair Landslide (LB landslide) on Whidbey Island, Island County, Washington occurred around 3:45 am on March 27, 2013.
- It is a small portion of a much larger landslide complex, approximately 1.5 miles long, that was prehistoric and may date back as far as 11,000 years.
- The top of the landslide scarp averages 200 feet above sea level.
- The landslide pushed (uplifted) the beach as high as 30 feet above the shore.
- The toe (front of landslide at the beach) is slightly over 1,100 feet long and extends approximately 300 feet into Puget Sound.
- Uplift of the beach is presumed to have been relatively slow (i.e., over a few minutes).
- Wave and tidal action is actively eroding the toe with small sections (1-10 cubic feet) observed calving with the rising tide.
- The volume of material moved was approximately 200,000 cubic yards (equivalent to 40,000 dump truck loads).
- DNR geologic mapping from 2009 shows the extent of the landslide complex (Polenz and others, 2009, http://www.dnr.wa.gov/Publications/ger_gm68_geol_map_camano_24k.pdf).
- Where observed, the access road has been shifted approximately 80 feet down vertically and to the west.