Five warning signs that a seaside cliff poses a falling hazard to beachgoers

Local officials are warning people of the dangers of relaxing on the beach underneath unstable cliffs. At Torrey Pines State Beach in San Diego debris from a recent cliff collapse could be seen on Thursday, Aug. 8, 2019.
(John Gibbins / The San Diego Union-Tribune)

Concerns about California’s crumbling seaside cliffs are on the rise after three people were fatally crushed at an Encinitas beach on Friday, Aug. 2 by a 30-foot slab of falling sandstone.

Beachgoers are routinely warned not to recreate under or walk atop bluffs, from Del Mar to San Francisco. As rising seas threaten to increase wave erosion on the state’s coastal cliffs, runoff from urban areas can weaken the often unstable rock formations from above.

Cities, such as Encinitas, direct people to keep a safe distance from bluffs of between 25 to 40 feet.

While scientists are increasingly studying coastal erosion in the context of the worsening climate crisis, even experts don’t know when the next collapse will strike.

However, there are a number of signs that a failure is more likely to occur at a particular location and that the effects of such a collapse could be disastrous.

Adam Young, a researcher at UC San Diego’s Scripps Institution of Oceanography, who has been tracking cliff erosion around the state, recently sat down with The San Diego Union-Tribune to discuss warning signs that beachgoers can be aware of:

1) Look for activity of a recent landslide, identified by freshly fallen rocks at the base of a cliff or a discolored section of the rock face.

“Landslides can happen over a period of days or even weeks, so if you see fresh activity down on the beach, it’s probably a good idea to go somewhere else,” Young said.

“It’s a little difficult for someone who doesn’t look at a lot of rocks, but what you want to look for is something that’s very angular, not rounded by the ocean yet,” he added.

2) Be wary of vertical and undercut cliffs. These formations are more likely to produce toppling collapses with free-falling material, rather than rolling landslides where the side of a cliff can slough off in a rolling, less dramatic fashion.

“Some of the really big landslides up in San Onofre are huge, but they are these big, rotational slides, and they move very slowly,” Young said. “Even though there’s a ton of land sliding, it’s not as hazardous as somewhere like Torrey Pines, where there’s very steep, vertical cliffs.

“Any sort of over-vertical features on cliffs, sea arches, those types of things are prone to fail,” he added. “They’re not stable. The overhang could be undercutting for years, and then it falls.”

3) Cracking in the side of a cliff is a strong sign it’s unstable, particularly if the cracking occurs on the top of the cliff.

“The ones to look out for are the ones parallel to the base of the cliff, which are difficult to see because they can be hidden inside the cliff, but when they propagate all the way to the top of the cliff, you can see them,” he said.

4) Look for water seeping out of the cliff. Ocean waves cause long-term erosion, but large surges of urban runoff can have a more immediate destabilizing effect.

“Particularly, if there are a lot of rainstorms in a row, chances are more likely a landslide will occur,” he said. “In the wintertime after a heavy rain, that’s something to be aware of. That’s not the best time to go to the beach.

“Think of it like Jenga,” he added “All it takes is one little piece, and then it falls.”

5) Stay farther away from taller cliffs, and consider visiting the beach at low tide when there’s more room on the beach to recreate further from the bluffs.

“The distance matters a lot,” he said. “A taller cliff is capable of throwing material further out onto the beach. So somewhere like Torrey Pines, it can get pretty far.

“These are things I look for when I go to the beach,” he added.

-- Joshua Emerson Smith is a reporter for The San Diego Union-Tribune