Swift Creek Landslide

The Swift Creek Landslide is an active, slow moving landslide located in western Washington, USA, due east of Everson on Sumas Mountain. Asbestos laden sediment originating from the landslide has recently generated much interest in this area.

Cause

Landslides in the Pacific Northwest are caused by a number of reasons. One is the geology of the area; layers of loosely consolidated sediments, such as sand, overlay strongly consolidated (less permeable) layers of sediments such as clays [Department of Ecology: Puget Sound Landslides. Retrieved March 1, 2008 from http://www.ecy.wa.gov/programs/sea/landslides/info/info.html] . That, in addition to the large amount of precipitation received in Washington state each year, makes for prime landsliding conditions.Earthquakes are thought to help trigger landslides in the Puget Sound, as well as things such as logging and wave erosion [Department of Ecology: Puget Sound Landslides. Retrieved March 1, 2008 from http://www.ecy.wa.gov/programs/sea/landslides/info/info.html] . The Swift Creek Landslide is thought to be a smaller reactivation of an older and larger landslide in that area; perhaps an earthquake set the older, then static landslide into motion.

Dynamics

This landslide is roughly half a kilometer in width, and 1.5 kilometers long. The depth of the landslide is approximately 100 meters. The velocity of the landslide varies, but the fastest moving part is at the toe, which moves upwards of 10 meters annually [Clark, D., Mckenzie-Johnson, A (2003) Dynamics of the swift creek landslide, northwest Washington. Geological Society of America Abstracts with Programs, Vol. 35, No. 6, p. 22. Retrieved March 1, 2008 from http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_60264.htm] . There is a lack of vegetation on the toe of the landslide because it is over steepened and constantly sliding, providing no stable area for trees to grow. The trees that are growing on the sides and front of the landslide are tilted and disturbed due to the constant motion of the land. However, there is a section of trees in the middle of the slide that are not disturbed and seem to be moving as a connected unit riding on top of the sliding ground. At the head of the landslide, there is pronounced , and on the sides of the slide, there is transform faulting.

Environmental and political implications

Over 120,000 cubic yards (92,000 m³) of sediment from the landslide each year is deposited into Swift Creek [Swift creek asbestos site (2007) US Environmental Protection Agency. Retrieved March 2, 2008 from http://yosemite.epa.gov/R10/CLEANUP.NSF/0903ae66d99736e188256f04006c2d3a/ae783c0f1916953c88257289006b3656!OpenDocument] . Due to the large amount of sediment being deposited in the creek, a preventative measure (dredging) was taken to prevent the creek from flowing over roads and flooding houses. The sediment collected by dredging the creek was given away free to use for projects such as building housing foundations or to be used as fill. In 2005, a study revealed that the sediment contains a naturally occurring form of asbestos. The EPA immediately put a ban on further dredging of Swift Creek and no longer allows the removal of previously dredged sediments. Old dredgings still remain piled alongside the creek and are covered over with soil to keep them from blowing away. There is a growing rift between the government and the people who live near Swift Creek. Soon, the sediment will build up enough causing the river to flood and destroy neighboring roads and properties, but because of the environmental and health risks that the EPA decided would be caused by this asbestos, nothing can be done to stop the flooding.

References