Voyager: With sea level rising, will cliffs along the coastline fall into the water?


Yes—at least where there aren't any seawalls.

Cliffs in California have been eroding for at least 18,000 years. That's when the glaciers began their latest episode of retreat as the earth warmed and we came out of the latest “ice age.” Over those 180 centuries, sea level rose more than 400 feet and the shoreline at Encinitas moved landward several miles. As the shoreline retreated, waves attacked the cliffs, which eroded and provided sand to create and maintain the beaches.

As sea level rise continues, erosion and retreat also will continue. Up to five feet of sea-level rise is possible over the next 100 years, although a three-foot rise is more likely. That might mean cliffs will erode hundreds of feet, if past rates are any guide.

Of course, with all the valuable development on cliffs – including homes, parks, businesses, roads, railroads, and lots more stuff ­– we can't afford to let these cliffs erode “naturally.” Instead, we build seawalls that protect the cliffs and the developments on them. But, seawalls don't protect the beaches, which depend on the sand in part from the eroding cliffs. Beaches also depend on sand deposited from rivers, although dams have greatly reduced the amount that reaches the beach.

So, yes, cliffs that aren't protected with seawalls will fall onto the beach and into the water. Those that are protected won't. But, as more cliffs get protected (and more rivers get dams), beaches will get narrower and may eventually disappear.

- Reinhard Flick, research associate, Integrative Oceanography Division

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