Pre-2014 mudslides at Oso revealed by InSAR and multi-source DEM analysis

The March 22, 2014 Oso mudslide at Washington was an extreme event costing nearly 40 deaths and damaging civilian properties. Historic record indicates that there have been serial events in decades. In our study, the combination of multi-source digital elevation models (DEMs), interferometric synthetic aperture radar (InSAR), and time-series InSAR analysis allowed us to characterize the Oso mudslide. The difference of shuttle radar topography mission (SRTM) and 2003 light detection and ranging (LiDAR) DEM indicated the topographic changes before 2006 mudslide, and the combination of time-series InSAR analysis and old-dated DEM (2000 SRTM, 2003 LiDAR DEM) revealed topographic changes associated with the 2006 sliding event. InSAR results from advanced land observing satellite (ALOS) phased array type L-band synthetic aperture radar (PALSAR) and LiDAR DEMs show that there were no significant topographic changes between 2007 and 2013 before the 2014 mudslide. The lasting toe erosion and logging near the landslide site could affect the 2006 mudslide event. Elevated discharges during wet seasons after 2006 accelerated the erosion of slumps deposited after the 2006 mudslide, which lessened the beneficial buttressing effect of the landslide toe with increased pore pressure during relatively higher rainfall after 2006. The vicious toe erosion within a relatively short period of eight years might play a critical role on the run-away event at Oso in 2014.