Ground sensors can help predict the collapse of cliffs along San Diego’s coast according to research conducted over four years by Scripps Institution of Oceanography scientists.

In a study published Thursday, researchers detailed how they used advanced sensors to track and predict coastal cliff erosion at three North County San Diego beaches. They include Beacon’s Beach and San Elijo State Beach in Encinitas, and the Railway corridor in Del Mar — known hotspots for bluff failure.

“The idea here with these sensor networks is really can we detect ground motion signals prior to one of those sudden collapses of a landslide,” said Adam Young, lead researcher and a coastal geomorphologist with Scripps institution of Oceanography at UC San Diego.

Young said over the course of the research the team predicted five cliff collapses hours to days before they happened at the sites.

The goal of the research was to analyze if developing an early warning system for coastal erosion is feasible.

“We were expecting to see some sort of signals prior to collapse, but it was surprising I think at how good the data turned out to be and how consistent it was for these types of landslides we were monitoring,” Young said.

The researchers used sensors, called tiltometers, buried on top of the cliff to monitor their stability. They measure changes in the cliff’s slope underground.

“The ground is creeping towards the ocean at a very small rate. You can't see it with your eye but we can monitor it with these sensors,” Young said.

The largest landslide they predicted dumped nearly 200 tons of rubble onto the beach in Del Mar in April 2024.

“We often saw cracking in the cliff top before we saw those catastrophic events,” Young said.

High tides, big waves and limited beach space often push beachgoers toward the cliffs.

Young said the results could lead to an early warning system that would make beaches safer, and even save lives. If a cliff failure is predicted Young and his team recommend some safety measures.

“You could temporarily close part of the beach, you could also close the cliff top. Again if it's an imminent failure you could actually go in, you could clear the area on the beach and proactively, mechanically detach it so nobody gets hurt,” Young said. “You could add additional signage to warn people of risk in the area.”

The study was made possible by state funding. Assemblymember Tasha Boerner, a Democrat whose District 77 includes Encinitas and Del Mar, wrote legislation following a local tragedy.

“In 2019 three women in our community died from a bluff collapse at Grandview Beach in Encinitas,” she said. “It was devastating but not unique to our area. Bluff collapses have taken lives throughout the states.”

Since 1941, 25 people have died from coastal landslides in California — 19 of those deaths happened in San Diego County, according to Scripps.

Boerner hopes the results of the study will eventually lead to a notification system that, “could give our cities enough warning to minimize deaths, injuries and damages.”

For Patrick Davis, the study is more than just a safety measure. It’s a resolution.

It was his wife, daughter and sister-in-law who were killed at Grandview Beach in 2019. Ever since, he’s advocated for public awareness around unstable cliffs.

He’s returned to the same spot where the accident happened and said most of the public doesn't seem to know that it’s dangerous.

He thinks the monitoring system is a great idea.

Researchers also looked at the impact of rainfall on coastal erosion by conducting weekly lidar cliff mapping from Torrey Pines State Beach to Encinitas.

Lidar is a laser-based technology that in this case was captured from a drone and vehicle-mounted device to create 3D maps of the bluffs.

A key conclusion of that research is the correlation between heavy rains and landslides.

For example, the researchers found a 70% probability of a large cliff failure within four weeks of a day that saw more than an inch of rainfall. That probability dropped to 20% if the area received no rain.

“Landslides are happening all times of year, but there are occasions when we have elevated rainfall conditions and we get elevated cliff erosion and landsliding activity,” Young said.

Young said the next steps include the need for the state to create plans for warning the public when a cliff is likely to collapse.

They're trying to get more federal funding to continue the research. Young said he hopes to expand monitoring to more locations, including Point Loma and other parts of California.