visitor put up by Jim Steele
printed within the Pacific Tribune July 24th
California’s spectacular shoreline attracts vacationers from world wide. Headlands of granite or basalt resist erosion, defiantly jutting out into the ocean. Pocket seashores kind the place targeted wave power bites into softer sandstones and uncemented stream sediments. Relentless waves undermine and steepen cliffs bordering 70% of California’s shoreline. Over a whole lot and 1000’s of years, pure erosion sculpted our awe-inspiring undulating coast.
However magnificence is within the eye of the beholder – likewise the magnitude of a “coastal disaster”. The Los Angeles Occasions not too long ago printed ‘California coast is disappearing underneath the rising sea. Our decisions are grim’. They inaccurately painted pure erosion as a latest disaster as a result of CO2 induced local weather change. Nevertheless, California’s erosion “disaster” have to be understood inside a larger timeframe.
Because the finish of the final ice age, sea degree has risen 400 toes. Over 18,000 years, San Francisco’s regional shoreline marched 25 miles inland, advancing 7 toes a yr – greater than twice California’s common. My stunning dwelling city of Pacifica was featured in that Occasions’ article as a result of it misplaced a number of houses sadly constructed on loosely cemented sand and gravel deposited 100,000 years in the past when sea degree was 20 toes greater. Though the ocean’s landward march has slowed over the previous 5000 years, northern Pacifica’s fragile shoreline nonetheless retreated by over 7 toes per yr between 1929 and 1943. Regardless of a warming world, the common charge of cliff retreat then markedly declined since 1943.
The ill-fated Ocean Shore Railway, initiated in 1905, foreshadowed California’s erosion issues. To present vacationers superior views, tracks have been laid on a ledge dug into steep coastal cliffs. However landslides have been frequent, and expensive repairs pressured the railway to shut. At this time, solely 25% of the railway ledge constructed by 1928 nonetheless exists. Undeterred, designers of California’s scenic Pacific Coast Freeway hoped to present vehicle vacationers related breath-taking views. Once more, landslides have been frequent. Solely 38% of the freeway constructed by 1956 nonetheless stays. Geologists inform us such landslides continuously altered California’s trendy shoreline for a whole lot of years.
There are few straight traces in nature. Our coastlines undulate. Likewise, our local weather oscillates, and coasts erode episodically. Between 1976 and 1999 (the nice and cozy part of the Pacific Decadal Oscillation), California skilled extra frequent El Niños. Over 70% of California’s 20th century disappearing shoreline eroded throughout El Niño occasions. El Niños deliver extra storms and extra damaging waves. El Niños deliver extra rains that saturate soils and promote landslides. The Pacific Decadal Oscillation then switched to its cool part. It introduced extra La Niñas and extra drought, however fewer winter storms and fewer erosion. In 1949, additionally a time of much less erosion, Pacifica’s authorities believed houses setback 65 toes from the sting of a bluff could be protected. They by no means suspected a single El Niño occasion would transfer the cliff edge 30 toes landward 50 years later.
There are some who see human buildings as a blight on California’s pure shoreline. In response to pure erosion, they counsel we abandon the coast. They argue California’s solely selection is “managed retreat” versus “unmanaged retreat”. Though effectively engineered seawalls can shield houses and companies, some environmentalists known as seawalls a coastal “disaster”. California’s Coastal Fee not too long ago pledged seawalls will “solely be permitted if completely needed”. However the Fee’s coverage solely fosters a mishmash of emergency fixes. Randomly armored properties deflect damaging waves downstream, accelerating erosion in a neighbor’s unprotected property. Coastal cities should assemble well-engineered sea partitions, with none gaps.
As a result of sea partitions forestall erosion, the Fee ill-advisedly fears native seashores will likely be misplaced if denied domestically eroded sand. The Occasions parroted that perception writing, ‘for each constructed seawall, a seaside is sacrificed’. However is that true? San Francisco’s O’Shaughnessy sea wall inbuilt 1929 prevents erosion of the delicate sand dunes supporting Golden Gate Park. But SF’s north ocean seaside continues to develop. And not using a seawall, San Francisco’s south ocean seaside quickly eroded, and threatened infrastructure now requires a sea wall.
Sources of seaside sand fluctuate, and simplistic sea wall analyses are very deceptive. Sand is saved and transported to seashores in some ways. Streams and rivers provide essentially the most sand wanted to nourish a seaside, however mining SF bay’s sand has disadvantaged close by coastal seashores. Moreover, ocean oscillations shift winds and the path of currents that transport sand. Seashores develop for many years then out of the blue shrink. Though some argue our seashores face a rising sea degree “disaster”, archaeologist decided that regardless of extra quickly rising sea ranges 5000 years in the past, many California seashores grew when provided with sufficient sand.
Lastly, it’s fascinating to notice scientists recommended Pacific islands additionally face an erosion disaster as a result of rising sea ranges. However the newest scientific surveys decided 43% of these islands remained secure whereas land extent of one other 43% has grown. Solely 14% of the islands misplaced land. So, I concern exaggerated crises solely erode our belief in science.
Jim Steele is director emeritus of the Sierra Nevada Subject Campus, SFSU
and authored Landscapes and Cycles: An Environmentalist’s Journey to Local weather Skepticism