New aerial photos of the massive new Big Sur landslide show that the California coast has expanded by a stunning 13 acres — the size of 10 football fields.
The historic three-dimensional images of our sudden growth spurt — an exhilarating event for a state used to watching its edges erode — is part of a project led by U.S. Geological Survey research geologist Jonathan Warrick, based in Santa Cruz.
“To witness the change of the coast in a constructional way — it’s such a unique event,” said landslide expert Kevin Schmidt of USGS in Menlo Park, who was not involved in the project.
“Typically, we are losing the battle to wave action,” he said. “It has been a number of decades since something this large increased our land mass.”
Images taken out the window of a Cessna 182 plane on May 27 — seven days after the landslide — show that 2 million cubic meters of earth have collapsed, Warrick found. That’s 200,000 dump trucks filled with rubble.
Highway 1, if it still exists, is buried under 80 feet of dirt and rock at its deepest point, his photos show. That’s a formidable excavation project for Caltrans — which has estimated it will take more than a year to reopen the road.
The movement extended almost all the way up to the crest of the Santa Lucia Mountains, at 1,100 feet in elevation.
The land that collapsed into the Pacific Ocean will not be excavated by Caltrans but will stay there, creating a new apronlike point on the coast.
“If you look around the world, almost everywhere we’re losing coast,” said Gary Griggs, professor of earth sciences and director of the Institute of Marine Sciences at UC Santa Cruz.
“There are only three places where we gain it: Hawaii, where new lava flows into the ocean, cools and we sell it for beachfront property; deltas, like the Mississippi, although that is low-lying, and then massive coastal landslides.” said Griggs, co-author of the book “Living With The Changing California Coast.”
Don’t expect the new California land mass to be permanent, Griggs said.
“It’s probably relatively short-lived,” he said. “It might take a couple years or a decade, but it will erode.”
Earlier images taken on May 19 show that it was already slipping. Images dating back to April also show a restless landscape.
“The success story is this: Caltrans sensed it was moving and got the crews out. Because of that, no one died,” Warrick said.
“That type of movement wouldn’t have been kind to people in the way,” he said. “That is the untold story here. Some folks got the message, understood the magnitude of this thing and pulled the crews off.”
Big Sur, where the mountains of the Santa Lucia Range rise dramatically from the Pacific Ocean, has some of the most complicated geology in California.
The southern part of the Santa Lucia Range, where the landslide occurred, is composed of diverse and contorted rocks — a jumbled mix of deep-sea sediments like shale, sandstone and chert, mixed with metamorphic rocks such as chert and basalt, according to Griggs.
To add to the chaos, this landscape sits astride the San Andreas Fault, so it is steadily moving northward.
This melange of materials creates weakness and instability, boosting the chances of a landslide, Schmidt said.
Two other things, he said, contribute to risk of landslide: the steep topography and the exposure to fierce Pacific storms. When rain hits, it saturates the mountains. Water fills every open pore between particles of soil, creating pressure and loosening the earth.
The USGS project started last year, with the goal of photographing the coast — from San Francisco to Big Sur — 10 times a year. Warrick hired pilot Bob Van Wagenen of Ecoscan Resource Data, based in Watsonville, to bring cameras 2,500 to 3,500 feet in the air and shoot at a 35-degree angle.
The plane makes two passes, with one photo shot every second.
Then all the images are integrated by computer to create a three-dimensional portrait of the changing coast.
“The goal is to develop databases so we can track changes along the coast, which we know is changing all the time,” Warrick said.
The project documents not just landslides, but also movements of cliffs, beaches, sand dunes and physical structures, such as homes in Pacifica.
As Caltrans struggles to fix the Mud Creek landslide, Warrick will photograph the site every week or two, then provide the data to the state.
“If we know what is going on,” he said, “we can help figure out how to plan for the future.”
