Researchers: Alexander L. Handwerger and Eric J. Fielding, Jet Propulsion Laboratory; Mong-Han Huang, University of Maryland; Adam M. Booth, Portland State University and Roland Bürgmann, University of California, Berkeley
Written by Linda Rowan
28 January 2020
Synthetic Aperture Radar (SAR) imagery and precipitation data of the Mud Creek landslide in California over 8 years, reveal the catastrophic failure was caused by a large increase in pore-fluid pressure. The increase was due to a record rainfall after a prolonged drought. Satellite imagery is an effective tool for observing landslide behavior, especially where ground-based instruments are not feasible to monitor unstable ground.
Landslides can be described as slow-moving, stable slides to fast-moving, unstable slides. Stress, fluid-pressure, and material properties determine how much and how quickly land will move. Stress and fluid-pressure can change based on water load, water storage, and fluid changes that are natural, such as rainfall or snowfall, or human-induced, such as wastewater injection.
The California Coast Ranges contain hundreds of slow-moving landslides that have been stably sliding for years to decades. Landslides are pervasive in these mountains because of the active uplift creating steep slopes, the composition of the rocks and soil (clay-rich matrices mixed with deformed sandstones, shales and schists) and the large and highly variable amount of precipitation.
Most of these slow-moving landslides do not fail catastrophically. The Mud Creek landslide did fail catastrophically on 20 May 2017. Satellite and airborne interferometric SAR (InSAR) data was gathered before, during and after the slide to measure its aerial extent, changing velocity and other details.
InSAR was collected between 2009 and 2017 for the Mud Creek, Paul’s and Boulder Creek landslides in the California Coastal Ranges. The Mud Creek slide experienced stable slow sliding for at least 8 years before its catastrophic, unstable, fast sliding. The slide averaged 0.43 meters per year towards the south, 0.24 meters per year towards the west and 0.17 meters per year vertically downward (subsiding). Between 2015 and 2017, the slide moved downhill continuously with small changes in velocity related to increased precipitation. 2015 was the last year of a prolonged drought, afterwards the slide began to move more with increased rainfall in 2016 and 2017. In May 2017, extreme rainfall combined with compaction and compression of the landslide material likely led to a large increase in pore-fluid pressure that brought the Mud Creek landslide to sudden and catastrophic failure. We can learn more from these observations; for example, some of the observed velocity changes of the slide cannot be explained by current models or conditions. SAR represents an excellent approach to following landslides and other land surface changes over small to large areas.
Handwerger, A.L., Huang, M., Fielding, E.J. et al. A shift from drought to extreme rainfall drives a stable landslide to catastrophic failure. Sci Rep 9, 1569 (2019), doi: 10.1038/s41598-018-38300-0 .
landslide, synthetic aperture radar (SAR), pore-fluid pressure
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Last modified: 2020-01-28 17:14:12 America/Denver