NASA radar imagery reveals how Los Angeles landslides accelerated due to rain

An analysis measuring the movement of slow-moving landslides on the Palos Verdes Peninsula in Los Angeles County found that land in the residential area slid toward the ocean by as much as 4 inches (10 centimeters) per week in the fall of 2024, NASA officials announced Friday.

The movement of land was accelerated and the active area expanded as a result of record-breaking rainfall in 2023, as well as heavy rains the L.A. region experienced in early 2024, according to researchers at NASA's Jet Propulsion Laboratory in Southern California.

"In effect, we're seeing that the footprint of land experiencing significant impacts has expanded, and the speed is more than enough to put human life and infrastructure at risk," Alexander Handwerger, the JPL landslide scientist who performed the analysis, said in a statement. Researchers used data from an airborne radar for their study.


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Parts of the peninsula are part of what researchers described as an "ancient complex of landslides" that has been moving for at least six decades, and affecting hundreds of buildings in local communities.

The JPL team created a map to show the active zone using data from four flights of its Uninhabited Aerial Vehicle Synthetic Aperture Radar between September and October 2024.

The UAVSAR instrument was mounted to a jet and flown out of NASA's Armstrong Flight Research Center in Edwards, California. The four flights were planned to estimate the speed and direction of the landslides in three dimensions.

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NASA sent the data to state officials in an effort to help the state respond to the landslides. The information was made available to the public and can be found at bit.ly/42D5JCT.

A team of researchers at the University of California, Los Angeles, found that a buildup of vegetation between 2022 and 2024, followed by the aforementioned dry conditions, made Los Angeles county a giant tinderbox. 2022 and 2023 were especially wet years for Southern California; according to a NASA Earth Observatory release, rainfall totals for downtown L.A. were nearly twice the average both years, according to data dating back to 1877.

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Portions of the peninsula, which juts into the Pacific Ocean just south of the city of Los Angeles, are part of an ancient complex of landslides and has been moving for at least the past six decades, affecting hundreds of buildings in local communities. The motion accelerated, and the active area expanded following record-breaking rainfall in Southern California in 2023 and heavy precipitation in early 2024, NASA said.

In the image above, colours indicate how fast parts of the landslide complex were moving in late September and October, with the darkest reds indicating the highest speeds. The arrows represent the direction of horizontal motion. The white solid lines are the boundaries of the active landslide area as defined in 2007 by the California Geological Survey.

“In effect, we’re seeing that the footprint of land experiencing significant impacts has expanded, and the speed is more than enough to put human life and infrastructure at risk,” said Alexander Handwerger, the JPL landslide scientist who performed the analysis.