A real cliffhanger for geologists
Like an axe slowly chopping at the trunk of a massive tree, waves driven by sea-level rise will hack away the base of cliffs on the Southern California coast at an accelerated pace, a recent study says, increasing land erosion that could topple some bluffs and thousands of homes sitting atop them.
California officials from Santa Barbara to San Diego will face an awful choice as the sea rises, the U.S. Geological Survey (USGS) study says: save public beaches enjoyed by millions, or close them off with boulders and concrete walls to armour the shore and stop the waves in a bid to save homes.
The study predicts coastal land loss on an unimaginable scale over the remaining century, up to 40 metres beyond the existing shoreline.
“For the highest sea-level rise scenario, taking an average cliff height of more than 25 metres, the total cliff volume loss would be more than 300 million metres by 2100,” it says.
One of the study’s authors, Patrick Barnard, a USGS research geologist, tried to explain the issue in a way that laypeople can understand.
“It’s a huge volume of material,” he said.
“We place this in a context of dump truck loads. It would be 30 million dump trucks full of material that will be eroded from the cliffs.”
The trucks would stretch around the globe multiple times, he said.
The USGS undertook the study to inform the state’s public planners and policy-makers of possible effects of climate change, which is causing the seas to rise. The analysis focuses on Southern California, but future studies will examine possible effects on the state’s central and northern coasts as well.
In the San Francisco area, officials have already retreated from some parts of the coast, removing homes from cliffs that have eroded and areas that have flooded.
San Francisco is taking steps to move the Great Highway away from Ocean Beach because erosion is eating away the earth beneath it. Houses and apartments in Pacifica, south of the city, were declared uninhabitable as cliffs that supported them gave way to erosion.
The study was published last month in the Journal of Geophysical Research. It predicts that by the end of the century, erosion in Southern California will double from the rates observed between 1930 and 2010, depending on how high the seas rise, as waves pound cliffs more frequently.
Barnard, who co-authored the study with fellow USGS researchers Patrick Limber and Sean Vitousek, along with Li Erikson of the University of Illinois at Chicago, acknowledged that the research was limited in the way it made predictions.