By Dave Tucker March 1, 2010
The Swift Creek landslide is on the west flank of Sumas Mountain, in Whatcom County east of the communities of Everson and Nooksack. It is a deep-seated, continually creeping landslide, best known to the public as the source of chrysotile asbestos in the sediment load of Swift Creek. The landslide is about 1.5 km long and 0.5 km wide. The moving mass consists predominantly of clay-sized grains of chrysotile, illite and hydrotalcite minerals weathered from serpentinite, a rock rich in the mineral serpentine. This mineral results from hydration of ultramafic rock, such as dunite, which occurs as pods on Sumas Mountain. Serpentinite blocks up to 1 foot across may weather into little more than muddy chips in only a year of so when exposed to rain. Bedrock along the lower margins of the landslide expose coarse boulder conglomerate of an alluvial fan facies of the Huntingdon Formation, correlative with the Eocene Chuckanut Formation. Large blocks of Huntingdon Formation litter the surface of the landslide above the toe. A nice article with on-the-ground photos appeared in Dan McShane’s “Reading the Washington Landscape’ web log at the end of January, titled ‘Whatcom County’s Desert‘. There is more detail there on the geology and activity of the Swift Creek landscape.
A time-lapse video shows 2.5 years of movement of the landslide. The photos were taken from a camera set up by Dr. Scott Linneman at Western Washington University’s Geology Department, and looks north over the surface of the landslide near its toe. The large Huntingdon Formation blocks seen on the surface are 10-20 feet tall.
Scott Linneman and his graduate students initiated geologic studies of the cause and dynamics of the Swift Creek landslide and its troublesome sediment. An abstract by Alex McKenzie-Johnson (2003), who completed his Masters research on the landslide during 2002-3, reports that surface velocity of the slide ranges from 2 to 37 m per year, depending on location on the slide; there is probably a correlation between heavy precipitation events and velocity. A study by another WWU graduate student, Tovah Bayer, discusses sediment yields and mineralogical origin of the sediment in downstream water, which is summarized in her 2006 GSA abstract. A 2009 abstract by S. Linneman further summarizes what is known about the dynamics, history and mineralogy of the landslide. Research at the landslide by WWU graduate students is ongoing. An Environmental Protection Agency website discussing the significance and potential health threat of the asbestos in this landslide and the sediment in Swift Creek is found here.
Getting there: This is strictly a virtual field trip. Access to the landslide is heavily restricted and is on private land, so no directions are given here. I strongly advise against trying to access the landslide, should you dare to pass the surveillance cameras and locked gates. For health reasons, special precautions are needed to safely visit the site.
References: In addition to links to websites, the following is recommended reading:
Linneman, S., Pittman, P., and Vaugeois, L., 2007, Lively landscapes: major Holocene geomorphic events in the Nooksack-Sumas valley: in Stelling and Tucker, editors, Floods, Faults and Fire: Geologic Field trips in Western Washington and Southwest British Columbia: Geological Society of America Field Guide 9, p. 99-119, doi: 10.1130/2007.fld009(5).
This volume is available for purchase online. The Bellingham Public library has a copy, as does the WWU library.