Potential Scenarios for Subaerial Landslides

Potential Scenarios for Subaerial Landslides
by Hugh Shipman, coastal geologist (WA Dept of Ecology)

Parameter Estimates Matrix -- Potential Landslide Scenarios

Area #1: Whidbey Basin

Location	Volume (m³)	Comments
Camano Head, S. Camano Island	100 K	Native accounts of landslide and tsunami at this location in 1830s [1].
Possession/Glendale area, Whidbey Island	100 K	* See note. Historic analogs might be 1900-era failure or 1980? Possession landslide.
NW shore Camano Island, Saratoga Passage	1-2 M	Topographic/bathymetric maps indicate possible large subaerial/submarine failure along shore north of Onamac Point. Age unknown.

Area #2: Port Orchard-Kitsap County

Location

Volume

(m³)

Comments

S side Illahee State Park, N of Enetai Beach.

100 K

* See note. Historic analog might be Brownsville slide.

Crystal Springs, Bainbridge Island

Possible topographic and geologic evidence for very large landslide. Age unknown. Adjacent to Seattle Fault.

Area #4: Vashon Basin

Location

Volume

(m³)

Comments

Point Evans, W side of Tacoma Narrows.

250K

Width: 200m

Height: 80m

Thick: 15m

High bluff, deep water, with evidence of multiple scales of landsliding. Height 70-100 m. Slopes >30-35 degrees.

Historical analogue: 1949 Salmon Beach slide?

*100,000 cubic meter scenario is based on historic landslides of same general scale, such as at Woodway (1997), Brownsville (1980?), and Possession Head (early 1900s).

[1] Shipman, H., 2001, The Fall of Camano Head: A Snohomish Account of a Large Landslide and Tsunami in Possession Sound during the early 1800s, TsuInfo Alert, 3, #6, 13-14. (http://www.wa.gov/dnr/htdocs/ger/tsuinfo/2001-06.pdf).