IDENTIFYING PRE-CURSOR SLIDE ACTIVITY FOR THE RATTLESNAKE HILLS LANDSLIDE IN WASHINGTON STATE

The slow moving Rattlesnake Hills landslide located three miles south of Yakima, Washington received great attention due to its potential to reach I-82, cross the Yakima River, and impact homes further to the south. The slide was extensively monitored by multiple agencies and consultants to understand the slide morphology, rate of movement, and potential runout scenarios after tension cracks were first observed in October 2017. This helped in gaining a comprehensive understanding of the slide's characteristics and potential impact. The landslide fortunately decelerated over time and has not reached I-82 to this day, but there is still more to be learned from the site. Interferometric synthetic aperture radar (InSAR) techniques have been widely used by scientists to study slow moving landslides across the world after movement has been physically observed, with special attention given to assessing rates of movement, including the Rattlesnake Hills landslide, but in terms of detecting pre-cursor slide activity and the timing of slide initiation, InSAR has been underutilized. For the Rattlesnake Hills landslide, we used the Alaska Satellite Facility Data Search - Vertex portal to generate interferograms derived from L1 Single Look Complex SAR data with the purpose of re-assessing when pre-cursor ground movement began to develop. Comparison of InSAR coherence imagery suggests pre-cursor ground movement began at least 1 year earlier than when tension cracks were physically observed in October 2017. Our results indicate that InSAR data should be more extensively used to monitor quarry sites and other sites with similar slow moving landslide potential. Quarry operators, agencies, and the public would benefit greatly from earlier detection of pre-cursor ground disturbances by implementing InSAR-derived early warning monitoring systems, as it could reduce loss, destruction, and post-movement monitoring costs for slow moving landslides.