Why landslides are suddenly tearing homes apart in Southern California

The Southern California community of Rancho Palos Verdes has always been as vulnerable as it is scenic.

Land beneath the city of 42,000 people has been slowly crumbling since long before multimillion-dollar homes perched over the Pacific Ocean. The Palos Verdes Peninsula, protruding from the flat Los Angeles basin at its southwestern edge, is made up of relatively weak rock and slippery clay, and it is subject to pounding waves.

Now, the delayed consequences of two stormy years in a row are demonstrating just how precarious that foundation can be. Slides that experts said are probably months if not years in the making are causing land that might typically move a few inches a year to slip by feet at a time, with rock slickened by historic rainfall that is still percolating deep underground.

That has damaged or destroyed homes atop Palos Verdes’s picturesque bluffs, and threatens hundreds of them. In recent days, landslides have forced power shut-offs, some of them indefinite, and warnings that evacuations could be necessary as authorities work to prevent damage from accelerating.

There had been hope in recent years that engineers could find a way to slow down the land movement, at least putting off a crisis like this one for years or decades. But the scale of the landslides occurring now means, according to one expert, “that ship has sailed.”

“It has unraveled into a disastrous situation,” said Kyle Tourjé, executive vice president of Alpha Structural, a Los Angeles engineering firm that responds to landslides. He said there are only two options for the hardest-hit parts of Rancho Palos Verdes: A massive and expensive effort by local, state and federal agencies to find a solution - if one even exists - “or total abandonment.”

Here is what to know about how the crisis came to be.

Landslides are constant in Palos Verdes

For residents along this stretch of coastline, feeling the earth move is nothing new - and not just because of earthquakes. The Palos Verdes Peninsula, home to the communities of Rancho Palos Verdes, Palos Verdes Estates, Rolling Hills and Rolling Hills Estates, has a history of landslides going back decades, though the current crisis is limited to sections of Rancho Palos Verdes.

The peninsula is composed of a mishmash of brittle shale and soft mudstone, according to the California Geological Survey - rocks so weak, you can break them apart with your hands, wrote one California State University at Dominguez Hills geologist.

And its prominence on the Los Angeles County coast, rising nearly 1,500 feet above the Pacific, makes those formations especially vulnerable to wind and weather. Ocean waves continually cut away from the bottom of the peninsula’s bluffs, making them ever steeper. And they provide a means for water to seep in, filtering underground to create slick planes where rock formations meet.

It is an area of especially fragile geology in a region that is known for it. Across the peninsula stretches a fault line that is lesser known than the San Andreas but that is capable of producing even more catastrophic earthquakes, a 2022 study found.

In Portuguese Bend, an area of Rancho Palos Verdes on the southern side of the Palos Verdes Peninsula, an active landslide has been ongoing since 1956, requiring constant repairs to one major roadway as the land moves more than eight feet per year.

Historic storms have exacerbated the landslides

Two historically wet California winters have hit Rancho Palos Verdes especially hard.

Most of the Golden State’s precipitation falls in a short window during the winter months, often in big storms carrying onslaughts of tropical Pacific moisture. And during the past two winters, some of those storms have brought massive amounts of rainfall to Southern California. As human-caused climate change raises average global temperatures, the atmosphere is capable of holding more moisture, making the downpours even more extreme.

The trend of intensifying winter storms is believed to be contributing to an epidemic of landslides on another picturesque section of California coastline around Big Sur, forcing repeated road closures and emergency repairs on the famed Highway 1.

One storm that hit Southern California in February dropped more than eight inches of rain on Los Angeles between Feb. 4 and Feb. 6, making that the city’s second-wettest three-day stretch on record. Downtown Los Angeles hasn’t seen so much rain within two years - more than 52 inches across the past two winters - since the late 1800s.

That storm immediately caused landslides to accelerate in Rancho Palos Verdes, while also threatening cliffside mansions elsewhere down the coast.

But worse landslide impacts take months, if not years, to develop. That’s how long it can take for rainfall to percolate to the depths at which the land beneath Rancho Palos Verdes may be moving, said Jonathan Godt, coordinator of the U.S. Geological Survey’s landslide hazards program.

“For water to make its way from rainfall down to those levels takes time,” Godt said. “Oftentimes it takes multiple years of wet weather for slides like that to move.”

Solutions - if any - are complicated and expensive

There is no quick and easy way to stabilize such a massive and fragile chunk of land. Much of the community’s focus in recent years has been on slowing the landslide as much as possible.

Rancho Palos Verdes received a $23 million federal grant from the Federal Emergency Management Agency last year to explore a strategy that officials hoped could limit land movement to just two inches per year. It would have pumped trapped water from beneath the peninsula and prevented rain from seeping underground in the future, in hopes that drying out the rock formations would help them become more stable.

The city’s mayor called it a “critical” project and a potential “game changer.”

But now, as the slides instead accelerate, “The situation is becoming more and more grim as each day goes on,” Tourjé said.

The Rancho Palos Verdes City Council was set to hold a special meeting Tuesday in response to the landslides. The main items on its agenda: imposing a local state of emergency, and asking California Gov. Gavin Newsom (D) to issue a state emergency declaration as the city grapples with how to help its residents.