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Geologic controls of slow-moving landslides near the U.S. West Coast

August 4, 2021

Slow-moving landslides, often with nearly imperceptible creeping motion, are an important landscape shaper and a dangerous natural hazard across the globe, yet their spatial distribution and geologic controls are still poorly known owing to a paucity of detailed, large-area observations. Here, we use interferometry of L-band satellite radar images to reveal 617 spatially large (4 ×">× 104–13 ×">× 106 m2) and presently active (2007–2019) slow-moving landslides near the populous US West Coast (only 4.6% of these slides were previously known) and provide evidence for their fundamental controls by bedrock lithology and vertical land motion. We found that slow-moving landslides are generally larger and more spatially frequent in homogeneous bedrock with low rock strength, and they are preferentially located on hillslopes with geologically recent uplift. Notably, landslide size and spatial density in the relatively weak metamorphic rocks and mélange (due to pervasive tectonically sheared discontinuities, foliation, and abundant clay minerals) were two times larger than those in sedimentary and igneous rocks, and the hillslopes with landslides were found to be uplifting approximately three times faster than the average for the whole region. These results suggest that slow-moving landslides can be effectively uncovered by satellite radar imagery and their occurrence and character may be anticipated from vertical land uplift and bedrock lithology. Hence, our study provides understanding critical for reducing landslide hazards and quantifying landslide impacts on landscape change.

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