Landslide zone in Los Angeles County is expanding

Today’s Image of the Day from NASA Earth Observatory features an active landslide zone that has been shifting for decades on the Palos Verdes Peninsula in Los Angeles County.

This area, particularly in Portuguese Bend, experiences ongoing ground movement, with land sliding toward the ocean at varying rates – sometimes moving several feet per year. 

The instability is largely due to weak, water-saturated bedrock and the effects of human activity, including road construction and irrigation, which have exacerbated the natural movement.

Analysis of the landslide zone

According to a recent report from NASA, the landslide zone on the Palos Verdes Peninsula has expanded. 

“Researchers at NASA’s Jet Propulsion Laboratory in Southern California used data from an airborne radar to measure the movement of the slow-moving landslides on the Palos Verdes Peninsula in Los Angeles County,” the report stated.

“The analysis determined that, during a four-week period in the fall of 2024, land in the residential area slid toward the ocean by as much as 4 inches (10 centimeters) per week.”

“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 that has been moving for at least the past six decades, affecting hundreds of buildings in local communities.” 

NASA noted that the motion accelerated and the active area expanded following record-breaking rainfall in Southern California in 2023 and heavy precipitation in early 2024.

Visualization of the landslide zone

To create the image, the Advanced Rapid Imaging and Analysis (ARIA) team used data from four flights of NASA’s Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) collected between September 18 and October 17, 2024. 

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

“In the image above, colors 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.”

Accelerating land movement and risks

Alexander Handwerger is a landslide scientist at the Jet Propulsion Laboratory who performed the analysis. “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 Handwerger. 

The landslide activity in this region dates back to the 1950s, when road construction projects disturbed the already unstable terrain, accelerating movement. 

Since then, shifting ground has led to significant damage to infrastructure, including cracked roads, broken utility lines, and distorted buildings. The instability has made it difficult for the city to maintain roads and essential services in the affected areas.

Despite efforts to slow the movement, including drainage improvements and engineering solutions, the land continues to shift. Homeowners and city officials have had to adapt, with some structures built to withstand slow movement, while others have been abandoned. 

The situation remains a challenge, with scientists monitoring the landslide to better understand its behavior and explore potential mitigation strategies.

Portuguese Bend is a well-known example of a continuously active landslide, highlighting the complex interaction between geology, human development, and environmental forces.

Image Credit: NASA Earth Observatory 

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