Nearly a month after a massive Big Sur landslide buried Highway 1 in millions of cubic yards of dirt and rock, geologists say it’s continuing to shift and change the shape of California’s coastline.
U.S. Geological Survey research geologists based in Santa Cruz are keeping a close eye on the 13 acres of new land near Mud Creek, about 9 miles north of the Monterey County line. A series of four slides on May 20 created the land mass, blocking coastal routes north of Ragged Point in San Luis Obispo County for at least a year.
And the slide isn’t done shifting, according to Jonathan Warrick, a USGS research geologist and Cal Poly alumnus.
“It was moving before (May 20), and it’s still moving around since,” he said.
Warrick and other geologists are using remote-sensing technology, such as aerial photos, satellite images and laser surveying tools, to track the slide’s movement. USGS researchers at the Pacific Coastal and Marine Science Center study the coastline from San Francisco to Big Sur in Northern and Central California and the Santa Barbara Channel from Point Conception to Point Mugu in Central and Southern California.
Researchers fly the coastline on different days and take photos of the slide from various angles. They then compare the images to find out where the slide has shifted.
Using colored 3-D models, researchers can show differences between the two flyovers — red-shaded areas indicate material has fallen away, while blue and purple spots indicate a higher elevation.
Sets of pictures taken on May 27 and June 13 show the slide continuing to move from the top down toward the ocean. A small access road Caltrans workers dug around the slide is also visible in the newer images.
At the base of the slide, known as the “toe,” waves breaking against the land mass have already begun to erode parts of it, Warrick said.
The California coastline has been shaped by landslides, although the Mud Creek Slide was unusually big, Warrick said. At least two decades worth of earth shifting likely contributed to that slide, he said: “We have had plenty of slides along this corridor, and we’ll have plenty of them in the future.”
USGS researchers are trying to help Caltrans figure out how to proceed as they begin to dig out Highway 1. In an area particularly prone to landslides, creating workable roads won’t be easy, Warrick said.
“It’s a challenging problem,” he said. “This is a dissertation to try and figure out.”