The Science of Predicting When Bluffs in Southern California Will Collapse

In August 2019, three women were strolling along the beach of Encinitas, California, north of San Diego, when the oceanfront bluff unexpectedly crumbled, showering them with tonnes of sandstone. One of the women, who had been celebrating her recovery from breast cancer, was killed instantly, while her sister and niece later died in the hospital.  That tragic event was neither the first nor the last bluff collapse in a scenic and densely populated, yet precarious, coastal region. Just a few kilometers to the south in Del Mar, a bluff collapsed following a rainstorm in 2016, undermining a busy coastal roadway. Sections of beachside cliffs came crashing down in the area in 2018, too, though no injuries were reported. In February this year, another bluff collapsed—along with the aging sea wall intended to hold it back—about 10 meters from the rail line that links San Diego and Los Angeles and serves nearly eight million passengers and numerous freight trains annually. - Smithsonian