Posted on September 14, 2022
Several of Humboldt County’s coastal cliffs rank among some of the fastest eroding bluffs in California, according to a recent study.
The cliffs on Centerville Beach and in the King Range ranked especially high on the list of California’s eroding coastal cliffs in the study, “Spatial and temporal trends in California coastal cliff retreat,” which found the Northern California coast is eroding at significantly higher speeds than the southern coastline.
The study noted that direct, quantitative relationships between cliff erosion and controlling factors are difficult to establish because of the inherent difficulty in measuring change in the rocks, especially since coastal erosion happens in spurts via landslides.
Humboldt County’s cliffs could be eroding faster than others in the state because of many factors, including the local weather and the substance of the cliffs, said Sam Flanagan, a geologist with the Bureau of Land Management’s office in Arcata.
“We get big storms, big swells, lots of ocean energy at the base of the bluff, and then a lot of these bluffs, Centerville in particular, are really young marine sedimentary material. It’s roughly 3 to 7 million years old,” Flanagan said. “It’s old uplifted seafloor that really hasn’t been around long enough to turn into hard rock, so it’s basically just a big pile of loosely consolidated sand that’s perched above and in a very unstable configuration.”
However, while cliff erosion in Humboldt County presents some dangers, the hazards are not as prevalent as places like San Diego, where earlier this year, three people were killed after a portion of a cliff caved in, crushing the victims under tons of sandstone. Humboldt County’s relatively sparse population and general lack of expansive development on coastal cliff — much of the coast is reserved for recreation — mean that dangers present themselves in the form of crumbling cliffs under the feet of hikers who venture too close to the edge.
A VW bus, which has since eroded, carved in the sand near Centerville Beach, one of the fastest eroding coastal cliffs in the state.
However, the environmental combination of sea level rise — a Humboldt County Civil Grand Jury released a report earlier this year detailing the effects of the projected three-foot rise in sea level — and climate change models which forecast hotter summers, but wetter winters, could further increase coastal erosion, Flanagan said.
Rising sea levels and increased coastal erosion leave communities with several options, said Gary Griggs, a professor of earth and planetary sciences who studies coastal erosion at the University of California, Santa Cruz. Communities can build sea walls — 13% of the coast has been armored with walls meant to break the tide — they can ignore the problem, they can truck in more sand on beaches, which he said was a short-term tactic, or they can engage in managed retreat, a strategy aimed at pulling back human structures from the coast.
“There are a lot of places where the cliff edge is getting close to somebody’s house,” Griggs said. “High tide is getting into their house, so somehow these cities and counties and homeowners have to come to grips with what’s happening and decide, is there a trigger point?”
King Salmon south of Eureka deals with annual flooding which routinely enters homes, though little damage was reported this year.
The civil grand jury’s report noted that three feet of sea-level rise will cause dramatic flooding in communities like King Salmon and Fields Landing and could cause Fairhaven’s septic tank systems to fail. The report also noted flooding could damage 9.6 miles of municipal water transmission lines, 30 electrical transmission towers and multiple environmentally hazardous sites on Humboldt Bay, such as the former pulp mill.
In 2016 and 2022, a 20-foot-tall, 15-to-30 ton cross commemorating the 1860 deaths of 38 people nearly toppled onto the beach as the cliffs eroded to its location. It now stands at the beach’s parking area.
Griggs said managed retreat is unpopular with homeowners due to the time, money and effort it takes to relocate farther back from the coast, but he noted that in Humboldt County, some cabins in Big Lagoon have already been moved back from cliffs, and Sonoma County will move parts of state Route 1 more inland.
“There’s nothing we can do in the long term to stop the Pacific Ocean from rising, the question is, when do we do something about it,” Griggs said.
