TIME-SERIES INSAR ANALYSIS OF CASCADE LANDSLIDE COMPLEX, WASHINGTON, USA

Detection of slow landslide movement in forested terrains has long been problematic, particularly for Cascade landslide complex in Washington, USA. Although parts of the landslide have been found reactivated, the timing and magnitude of landslide motions have not been systematically monitored. Here we apply time-series interferometric synthetic aperture radar (InSAR) strategies to map the landslide movement using two overlapping L-band ALOS-1 PALSAR-1 tracks. Our results show that the reactivated part of the landslide moved similar to 700 mm downslope between 2007 and 2011. The seasonal oscillations are correlated with precipitation records, suggesting the landslide motions are hydrologically driven. The temporal frequency of landslide motions is similar to that of GPS-derived regional ground oscillations but the former has much larger magnitude, suggesting stronger hydrological loading effects. Analysis of time-series radar amplitude on the headscarp allows us to re-evaluate the incipient motion of 2008 Greenleaf Basin rock avalanche.