Researchers at UC San Diego’s Scripps Institution of Oceanography conducted a first-of-its-kind scientific survey measuring the rate California’s coastal cliffs are collapsing into the Pacific. Their findings indicate that the cliffs of the iconic Lost Coast, the coastline straddling the Mendocino and Humboldt County border, are crumbling into the sea faster than any in the Golden State.
Researchers used a laser-imaging technology known as LiDAR (Light Detection and Ranging) to measure cliff erosion and retreat, comparing findings gathered between 2009-2011 to more recent data from 2016.
Scientists identified “hotspots”, locations in California experiencing the highest rates of cliff erosion, that many residents of the North Coast are well acquainted with. In Mendocino County, Caspar Headland State Beach near the town of Mendocino and Usal Beach, the southern terminus of the Lost Coast, are measurably collapsing faster than most of the state’s beaches.
Humboldt County’s hotspots include the northern stretch of the Lost Coast known as King Range, Centerville Beach located five miles west of Ferndale, and the McNeil Creek area north of Trinidad Head.
In 2016, Centerville Beach’s crumbling cliffs threatened a historic cross erected to memorialize the 1860 sinking of a steamer known as the Northerner off the coast. The cliff underneath where the cross had been installed began to collapse and the Native Sons of the Golden West volunteered to bring the cross to safety in January of 2017 before it tumbled down the crumbling cliff.
Del Norte County made the list approximately two miles north of where the Klamath River enters the Pacific. Those cliffs are also crumbling faster than most of the others in California.
Cal Poly Humboldt Professor Lori Dengler has spent her career exploring the North Coast’s seismic activity and the tsunamic hazards along our coastline. The coastline between 39-41 degrees latitude “consistently has the largest” waves, Professor Dengler said. With these larger waves plus high rainfall typical of the region, “you have all the ingredients for high erosion.”
For those that might be concerned that cliff retreat and sea-level rise could erode the iconic cliffs of the Coast, Professor Dengler said she doesn’t “think the bluffs will erode away completely anytime soon – the uplift is growing the coast at the same time.”
The Lost Coast is California’s most remote and least developed coastline. The untouched, primordial condition could be one of the contributing factors to its higher rate of retreat. The totality of the Lost Coast is considered “unarmored”, as opposed to “armored” which describes the installation of seawalls and riprap at the base of coastal cliffs to mitigate erosion. Cliff armoring is a common strategy employed in Southern California to reinforce and mitigate erosion, often associated with seaside development.
20% of SoCal’s coastal cliffs are armored. In contrast, only 1.5% of coastal cliffs in Northern California are armored, leaving them exposed to the full brunt of the Pacific. The Scripps study found that cliff retreat rates were twice as high for unarmored cliffs compared to those with human-made forms of reinforcement.
Another commonality noticed by researchers between cliffs collapsing the fastest might seem counterintuitive: cliffsides fronted by beaches retreated twice as fast as those without. Though a wide, sandy beach could suggest a barrier to protect cliffs from wave action, researchers found that beach sand, stirred up by incoming waves, acts as an abrasive, eroding the lower sector of a cliff. Caspar Beach, Usal Beach, large swaths of King Range, and Centerville Beach all feature sand beaches that end abruptly at steep cliff walls
This research was the outgrowth of California State Assembly Bill AB-66 which funded scientific research to build a deeper understanding of California’s coastline, coastal bluff failures, and the possible development of future alert systems to warn communities of cliff failures. Essential infrastructure including highways, public access points, homes, military bases, power plants, and railways are located along California’s coastline and are vulnerable to erosion, retreat, and collapse.
Perhaps a reassuring finding from the Scripps scientists is the fact some of California’s fastest crumbling cliffs are also the most remote and least inhabited. The steep cliff sides of the Lost Coast thwarted the vision of engineers when constructing California’s iconic Pacific Coast Highway. Originally, engineers envisioned the highway continuing along the coast but in 1984 concluded the rugged terrain of the Lost Coast made construction unfeasible and instead deviated inland connecting Rockport to Leggett.
Now, the stretch of coastline referred to as the Lost Coast which hosts multiple cliff retreat hotspots is actually made up of two separate designated wilderness areas.
The federally managed King Range Wilderness makes up the northern section of the Lost Coast, beginning just south of where the Mattole River enters the Pacific and ending near the town of Shelter Cove.
The southern section of the Lost Coast lies within Sinkyone Wilderness State Park, managed through a partnership of ten indigenous tribes known as the InterTribal Sinkyone Wilderness Council and California State Parks. Sinkyone Wilderness begins at Needle Rock Visitor Center and runs south to Usal Beach, a popular car camping destination.
The Lost Coast has very few permanent residents and does not host any critical infrastructure. But, the remote and rugged landscape that was deemed impassable makes it a sought-after destination for outdoor enthusiasts worldwide. Multiple big-name outdoor companies charge upwards of $2000/person for guided backing packing trips along the Lost Coast. Shuttle companies, owned and operated by locals, service hikers who park their vehicles at one end of the wilderness, hike to the other, and require a lift back to where they began. Businesses along the way to the Lost Coast prove last-minute opportunities for food or supplies before hitting the trail. The wilderness brings in a steady flow of visitors and tourism dollars to Mendocino and Humboldt Counties.
Researchers behind the Scripps study intended for their data set to inform coastal planning and development, essential in California where millions live a stone’s throw from where the American continent drops off into the Pacific. The oceans are rising. Policymakers in Mendocino and Humboldt County have already begun to consider the implications of this on our coastlines. Knowing sections of our coastline are crumbling at a record rate, perhaps local leaders will face the challenge of mitigating the negative effects of sea-level rise with a renewed sense of urgency.