A Southern California city that sits atop an ancient—yet active—landslide now faces a new problem as city geologists have discovered land movement deeper underground than initially expected, which they say changes everything.
“We now realize it is this larger, deeper, slip plane that is moving, which is why our project that we’ve been working on since 2017 ... has to change,” Rancho Palos Verdes City Manager Ara Mihranian said during an Aug. 20 city council meeting.
City staff and geologists said they learned of the deeper land movement after boring holes into the ground as part of a project to install “hydraugers”—which are horizontal draining pipes—to help remove ground and surface water, which triggers the movement.
Over the past few years, in an area known as Portuguese Bend, land movement has been constant at about three to four feet per month for the Portuguese Bend Landslide Complex—which includes multiple areas of ancient landslide ruins in what’s known as the Portuguese Bend community.
Described as a bowl within a bigger bowl, the Portuguese Bend Landslide Complex sits about 80 to 180 feet below ground. The Ancient Altamira Landslide Complex is underneath it and sits about 245 to 345 feet below ground, geologists say. This deeper landslide has the potential to move upward of 50 feet per year, which is faster than any of the others.
Until now, the city has been focusing on slowing down movement for the shallower landslides in Portuguese Bend, where 135 homes earlier this month had their gas shut off due to the land moving roughly three to four feet per month. The city declared a local emergency on Aug. 6 over the gas shutoffs to seek federal and state aid.
During a presentation, the city’s public works director Ramzi Awwad said the new discovery requires immediate action to tackle the deeper “slip planes”—the section of land moving underground—and redirect attention from the shallower slip planes.
“There’s no record of any movement on that deeper slip plane. So, this is again an unprecedented new scenario for the city, which means that we have to change our strategy,” Awwad said.
City staff said they will return to the council’s next meeting on Sept. 3 with construction contracts to at least “get a shovel in the ground,” either with the use of hydraugers or vertical dewatering wells.
Recent Developments
On the surface, movement has accelerated in recent years due to heavy rain. During the 2022 winter, the city received 200 percent more rainfall than average, creating slippery ground conditions. The Portuguese Bend landslide is now moving nine to 12 inches per week, according to city officials.In the 2023–2024 fiscal year, the city has spent more than $2.2 million in repairs and maintenance of Palos Verdes Drive South due to land movement.
Residents whose gas was shut off in late July also face threats of losing their power, provided by Southern California Edison. The land movement threatens to tumble electricity poles, which could spark fires, according to Southern California Edison (SCE).
An SCE spokesperson said as the ground moves, electricity poles can lean and cause tension or slack to power lines, which can be dangerous.
“We know this is a difficult time for this community. The safety of our employees, customers, and communities remains our top priority,” spokesperson Reggie Kumar told The Epoch Times in early August.
He said the utility is regularly inspecting its electrical equipment in the area with helicopters, ground crews, drones, and all-terrain vehicles and is installing sensors to detect whether electricity poles are moving.
Last year, two Rancho Palos Verdes homes were red-tagged in the spring, and several dirt trails and roads washed away due to the land movement, according to city officials.
Previously, SoCalGas said the decision to shut off service came after several months of closely monitoring the situation with the help of city officials and third-party experts.
During the process, workers relocated more than 600 feet of gas pipeline, added flexible pipeline joints to allow for some land movement, and installed an isolation valve to quickly shut off gas flow in case of an emergency, gas officials said on July 30.
They also said some assistance is available for the affected homeowners, including a one-time payment of $2,500.
