Clambering at low tide over its shelves of exposed reef bedrock, nicknamed “the Boneyard,” is a cold-pit-in-the-stomach experience that reveals how Mavericks’ unusually heavy waves are generated: cold ocean abruptly slams into geology.

Swells meet a craggy seafloor formed during the Pliocene era, and up lurches a colossal triangle of water that can chase a surfer such as Washburn down its steep face at speeds of 40 to 50 mph — fast enough that a wipeout will make a body skim like a stone in the avalanche.

One of the great big-wave amphitheaters in the world, an outcropping about 25 miles south of San Francisco, is being visibly reshaped by severe climate events, and Washburn, an unofficial elder statesman of Mavericks who has done documentary work and co-wrote a book about it, has a front-row seat.

Recent data from the Scripps Institution of Oceanography using lidar laser imaging computed that central California coastal erosion — realized episodically from high tides, big surf, groundwater surge, rainfall and sea-level rise — averaged 0.1 to 0.2 meters per year between 1998 and 2016.

It’s a spotter buoy that belongs to Sofar Ocean, a local tech firm co-founded by Janssen to provide real-time data on atmospheric conditions at sea through vast networks of sensors, intended for the dual purposes of commercial use and climate change study.

One day, unforeseen rogue sets from an Asian typhoon caught the best big-wavers in the world off guard, causing horrendous wipeouts that “look like someone blew up a garage next to me, with pieces of boards and all this flotsam in the water,” Washburn says, necessitating rescues.