Imaging Pre-failure Movements of Landslides along the North Fork Stillaguamish River valley\\ 

The recent, March 22 2014, Steelhead Haven slide is a tragic reminder of our vulnerability to devastating landslides in the Pacific Northwest (PNW). Steelhead Haven was an expansion of the 2006 Hazel Slide, and a continuation of the landslide history of the North Fork Stillaguamish River valley. In this work three winters will be examined to determine if pre-slope movements along the 2006 Hazel and Skaglund Hill slides rise above background noise, and show accelerating movement or other signs of imminent failure. Pre-failure signals detected in this work could be the first step in developing a precipitation-induced landslide hazard flag for the region, expanding previous work at the outcrop scale relating pre-failure movements to mode-of-failure (e.g. Petley et al., 2002). 

Study Site: The North Fork Stillaguamish has incised steep hillslopes in glacial-fluvial outwash, till, and glacial-lacustrine deposits (Keaton et al., 2014) that have been host to many historic and recent landslides (Haugerud, 2014). On January 25, 2006 the Hazel landslide occurred just above the Steelhead Haven community. Regular failures have occurred on this slope, most recently this past March. A partially denuded slope, clear-cut land above, and homes below provide potential reflectors for SAR. In February 2006 cracks were observed just downriver of Oso at the Skaglund Hill site, leading to a $13.3M WSDOT remediation project to prevent losses to the road and utility lines located at the toe of the slope.

Available Data: Data within the Stillaguamish is available along a single track (156) and frame (2637) at ~1month intervals for three winter seasons. ENVISAT data hosted at WinSAR are available for 2005-09-30 through 2006-01-13, 2004-09-10 through 2005-01-28, and 2001-09-21 through 2002-02-08. In total, the WInSAR archive contains 13 scenes. 10 interferograms could be developed from these data assuming incoherence beyond ~1month will prevent additional Interferograms. Additional scenes are available along different tracts but were not collected as regularly as track 156. These three collection years will be used to construct non-failure and pre-failure movement images to see if any precursory signals are present in the data. The frame used for these data, 2637, encloses the western Cascade range from route 2 in the South to route 20 in the North, spanning a large area where other slides might be detected. LiDAR elevation data taken in 2003 is available for the N. Fork Stillaguamish River valley and will provide high-resolution pre-2006 failure topography. Should ENVISAT data prove to be too incoherent to use within the study site, ALOS data from the winter of 2010-2011 is available at ~1month intervals, and could capture the 2011 reactivation of the Skaglund Hill slide. From Oct 28, 2010 to March 15, 2011 seven ALOS scenes could be processed into interferograms.

Deep soil slides, like the ones studied in this work, are driven by the development of pore pressures in the substrate during the wet PNW winter. These, and similar, slides may show pre-failure expressions as the resistance to sliding diminishes over time leading up to their collapse. Petley et al (2002) show relationships between pre-failure movement and mode-of-landsliding for field studies, while hinting at the capabilities of InSAR to perform this type of observation for landslides. This work seeks to explore the possibility of satellite-based landslide monitoring for the PNW through the pre-failure analysis of two known slides.

References:\\
Haugerud, R. A., (2014). Preliminary Interpretation of Pre-2014 Landslide Deposits in the Vicinity of Oso, Washington, U.S. Geological Survey Open-File Report 2014-1065, U.S. Geological Survey, Reston, http://dx.doi.org/10.3133/ofr20141065. \\ 
Keaton, J. R., Wartman, J., Anderson, S., Benoit, J., deLaChapelle, J., Gilber, R., and Montgomery, D. R., (2014). The 22 March 2014 Oso Landslide, Snohomish County, Washington. GEER Association Report No. GEER-036, 136p. \\ 
Petley, D. N., Bulmer, M. H., & Murphy, W. (2002). Patterns of movement in rotational and translational landslides.ʭGeology,ʭ30(8), 719-722.