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“Your chance of not being injured is hugely increased if you never walk near a cliff edge or the base of a cliff—that’s our recommendation,” John Dell’Osso, the seashore’s spokesman, said.   David Briggs

A new report out of Scripps Institution of Oceanography at the University of California San Diego found that the coastline of the Point Reyes National Seashore has some of the highest rates of cliff erosion from the Mexican border to Bodega Head. The study’s author, Adam Young, an assistant project scientist at the oceanography division, said it is the first large-scale project to use Light Detection and Ranging, or LiDAR, aerial data to get highly accurate, detailed maps of the coast. (Imagine planes flying over coastlines with a laser pulsing a couple of hundred times every second.) To show cliff changes over time across the majority of the state’s coastline, Mr. Young used three time periods, comparing two LiDAR data sets 11 years apart (one from 1998 and the other from 2010 to 2011) with historical records from the early 1930s. In Point Reyes, Mr. Young noted that between 1998 and 2010, clifftop retreat rates were about 10 to 12 feet per year in some locations, far above the average rate in his study of a third of a foot. He noted that the cliffs around Double Point, which is near Alamere Falls on the southern end of Point Reyes, experienced especially significant steepening between 1998 and 2010, increasing the potential for cliff-top failure. “We noticed that the areas where the rates of retreat were highest also have the greatest variance of rates between time periods,” Mr. Young said, explaining that this was because the high rates of erosion were likely due to large, single events. These seemed to be followed by more stable periods, but Mr. Young said that “timescale” pattern was the ground for further research. Park spokesman John Dell’Osso said there have been some horrific incidences of cliff collapse in the past few years at Arch Rock, Chimney Rock and Tomales Point. “This is not an unknown hazard; it is something that has gone on and will continue to go on,” he said. Though, he also cautioned: “Your chance of not being injured is hugely increased if you never walk near a cliff edge or the base of a cliff—that’s our recommendation.”