California's scenic coastal cliffs, which constitute approximately 70% of the state's coastline, are experiencing rapid erosion and collapsing into the sea, according to a new study by the University of California, San Diego.
The research identified hotspots of significant cliff erosion in Northern and Central California, including Humboldt, San Francisco, San Mateo, and Monterey counties. In some of these areas, the coastline is retreating at rates exceeding 30 feet and even up to 70 feet annually, presenting a considerable risk to coastal communities.
"The cliffs are not stable. They erode and collapse over time," said Danghan Xie, the study's lead author. "We’ve seen many sad news stories about fatal cliff landslides."
Researchers pointed to the Lost Coast Headlands in Humboldt County as a notable example, where the cliff top eroded by approximately 73 feet per year between 2016 and 2023. This period also saw a massive landslide involving over 1.4 million cubic yards of rock and soil.
Adam Young, a coastal geomorphologist at UC San Diego, emphasized the severity of the erosion rates, stating that 70 feet per year is substantial, amounting to more than the length of a football field over the seven-year study period.
Rates of cliff top retreat of 10 feet or more per year were also observed along other notable coastal areas, including the King Range, Redwood National Park, Point Reyes National Seashore, Big Sur, Vandenberg Space Force Base, and Palos Verdes.
Overall, the study found that 65% of California's cliffs showed measurable changes over the study period. Using lidar imagery from 2016 and 2023, researchers determined that, on average, the cliff tops across the state eroded about 1.6 inches per year.
The study's findings may be particularly relevant given the potential for a historically strong El Niño to generate unusually powerful waves and tides, which could exacerbate coastal erosion.
Scientists at UC San Diego have developed a California Coastal Cliff Erosion Viewer website, which allows the public to examine erosion rates along different segments of the coast. The website is expected to be updated periodically with new lidar data.
Understanding the locations and speed of cliff erosion is vital for public safety, especially concerning landslides. In Northern California, landslides have frequently led to the closure of sections of Highway 1, resulting in costly repairs and, tragically, loss of life. A landslide in Humboldt County last year, for instance, resulted in the death of a contractor working for the state transportation department.