EXPLAINER: Tackling threat of mudslides in soaked California

Jan 16, 2023, 11:24 AM

A mudslide covers the roadway just south of Mill Creek on California Highway 1. (Caltrans District ...

A mudslide covers the roadway just south of Mill Creek on California Highway 1. (Caltrans District 5/Twitter)

(Caltrans District 5/Twitter)

SAN DIEGO (AP) — Relentless storms from a series of atmospheric rivers have saturated the steep mountains and bald hillsides scarred from wildfires along much of California’s long coastline, causing hundreds of landslides this month.

So far the debris has mostly blocked roads and highways and has not harmed communities as in 2018 when mudslides roared through Montecito, killing 23 people and wiping out 130 homes.

But more rain is in the forecast, increasing the threat.

Experts say California has learned important lessons from the Montecito tragedy, and has more tools to pinpoint the hot spots and more basins and nets are in place to capture the falling debris before it hits homes. The recent storms are putting those efforts to the test as climate change produces more severe weather.


California has relatively young mountains from a geology standpoint, meaning much of its steep terrain is still in motion and covered in loose rocks and soil that can be sloughed off easily, especially when the ground is wet, according to geologists.

Almost all of the state has received rainfall totals of 400% to 600% above average since Christmas, with some areas receiving as much as 30 inches of precipitation, causing massive flooding. The severe weather has killed at least 19 people since late December.

Since New Year’s Eve, the California Department of Conservation’s landslide mapping team has documented more than 300 landslides.

The state’s prolonged drought has made matters worse.

Dan Shugar, an associate professor of geoscience at the University of Calgary, said drought can have a counterintuitive effect when combined with the incredible rainfall California has seen in recent days.

“You’d think if the ground is dry it should be able to absorb a lot of water, but when ground becomes too dry, the permeability of the ground actually decreases,” he said. As water runs off the hardened soil, moving downward and picking up energy, it can begin carrying soil and debris away, he said.

Added to that, wildfires have left some hillsides with little to no vegetation to hold the soil in place.


The most vulnerable areas are hillsides that have burned in the past two to three years with communities below them, said Jeremy Lancaster, who leads the California Department of Conservation’s geological and landslide mapping team.

That includes areas that recently burned in Napa, Mariposa, and Monterey counties, he said.

In 2018, the deadly mudslides in Montecito occurred about a month after one of the largest fires in California’s history tore through the same area, charring 280,000 acres.

Montecito is sandwiched between the Santa Ynez mountains and the Pacific coast. On the fifth anniversary of that tragedy, the entire community was ordered to evacuate on Jan. 9 as rains pummeled the area and debris blocked roads.

Lancaster warned that the threat of landslides will linger long after the rains have subsided as the water seeps 50 to 100 feet into the soil, dislodging things.

“They can occur weeks later, if not months,” he said.


Lancaster said California has dramatically increased its efforts to identify hotspots since the Montecito mudslides. His department continually updates its map so local communities are aware and can make decisions, including whether to evacuate an entire community.

The state is also working on a system to better pinpoint how much rain might trigger a landslide.

Marten Geertsema, who studies natural hazards and terrain analysis at the University of Northern British Columbia, said agencies use a variety of tools to gauge the likelihood of landslides in a given area, including terrain maps and lidar – pulsed light from lasers to penetrate foliage to see the ground. Then they can watch for early warnings, such as changes over time in photos taken from the air, or from satellites, or in data from GPS monitoring stations, tilt meters and or other on-site instrumentation.


One of the best ways to manage landslides is with debris basins – pits carved out of the landscape to catch material flowing downhill.

But basins, which can require a lot of land, can also disrupt the natural ecosystem and lead to beaches needing to be replenished by collecting sediment that flows out of the canyons, according to experts.

And they are costly, said Douglas Jerolmack, a professor of environmental science and mechanical engineering at the University of Pennsylvania. And if old debris isn’t removed, they can be overwhelmed by new landslides or mudslides.

Some might also not be big enough to deal with future slides worsened by climate change, Jerolmack said.

After the 2018 mudslides hit Montecito, the Los Angeles Times reported that debris basins above the community were undersized and hadn’t been sufficiently emptied.

The tragedy galvanized the community, which raised millions to address the problem, said Patrick McElroy, a retired Santa Barbara fire chief who founded the nonprofit organization, The Project for Resilient Communities.

The organization hired an engineering company to map the canyons and installed debris nets. He said the recent storms put them to the test: One net measuring 25 feet tall filled nearly to capacity.

McElroy said he’s still haunted by memories from 2018 but feels better, knowing that the community might be safer now.

“I’m not over it yet. But to wake up, you know, the other day and see no injuries and no fatalities. I just can’t tell you how impressed I am,” he said of the nets.

The best solution for the Montecito and Santa Barbara area is to have both nets and debris basins, according to Larry Gurrola, the engineering geologist hired by the organization.

But nothing is cheap. Santa Barbara County’s spent $20 million on a new basin after 2018, while McElroy’s organization spent close to $2 million on installing the nets, which includes liability insurance and other fees. They have a five-year permit for the nets, which will be removed if it is not renewed.

Gurrola said the alternative is more costly. With the recent storms, more than half of California’s 58 counties have been declared disaster areas and repairing the damage may cost more than $1 billion.

“Most importantly these things protect the community and save lives,” he said.


Glass reported from Minneapolis.

KSL 5 TV Live

National News

Idaho State Police released aerial photos of a string of crash sties on Interstate 84 on March 4, 2...

Mary Culbertson

63 cars, semitrucks crash on I-84 following winter storm

Idaho State Police responded to a string of crashes on I-84 Monday morning, closing miles of the interstate for hours.

1 minute ago

Tova Callender, left, and Christiane Keyhani of Hui O Ka Wai Ola, collect water samples at the Mala...

AUDREY McAVOY Associated Press

In Hawaii, coral is the foundation of life. What happened to it after the Lahaina wildfire?

For now, state officials are urging the public to limit their exposure to the ocean and seafood until scientists understand what might be making its way through the food chain.

1 hour ago

Cookie Monster has taken to X to express his frustration over shrinking products, aka: "shrinkflati...

Bryan Mena, CNN

Even Cookie Monster is complaining about the US economy now

Cookie Monster has taken a stance on a very real and controversial trend in the US economy — and he hates it.

2 hours ago

Thousands of pounds of Trader Joe's chicken soup dumplings have been recalled due to possible conta...

Jamie Gumbrecht, CNN

61,000 pounds of Trader Joe’s chicken soup dumplings recalled due to possible contamination with hard plastic

More than 61,000 pounds Trader Joe’s steamed chicken soup dumplings are being recalled due to possible contamination with hard plastic from a permanent marker.

2 hours ago

The Federal Aviation Administration has found multiple problems with Boeing’s production practice...

Pete Muntean, Gregory Wallace and Chris Isidore, CNN

FAA finds ‘multiple instances’ of Boeing quality control issues

The Federal Aviation Administration has found multiple problems with Boeing’s production practices following a six-week audit triggered by the January 5 door plug blowout on an Alaska Airlines’ Boeing 737 Max 9.

2 hours ago

FILE: The sun is seen in full eclipse over a park on Aug. 21, 2017, in Hiawatha, Kansas. Millions o...

Josh Ellis

Utahns will have to travel to catch the best part of April’s total solar eclipse

2023's eclipse gave thousands of Utahns a chance to see its "ring of fire," but the 2024 total solar eclipse will require some travel to get the full experience.

3 hours ago

Sponsored Articles

Modern chandelier hanging from a white slanted ceiling with windows in the backgruond...

Lighting Design

Light Up Your Home With These Top Lighting Trends for 2024

Check out the latest lighting design trends for 2024 and tips on how you can incorporate them into your home.

Technician woman fixing hardware of desktop computer. Close up....

PC Laptops

Tips for Hassle-Free Computer Repairs

Experiencing a glitch in your computer can be frustrating, but with these tips you can have your computer repaired without the stress.

Close up of finger on keyboard button with number 11 logo...

PC Laptops

7 Reasons Why You Should Upgrade Your Laptop to Windows 11

Explore the benefits of upgrading to Windows 11 for a smoother, more secure, and feature-packed computing experience.

Stylish room interior with beautiful Christmas tree and decorative fireplace...

Lighting Design

Create a Festive Home with Our Easy-to-Follow Holiday Prep Guide

Get ready for festive celebrations! Discover expert tips to prepare your home for the holidays, creating a warm and welcoming atmosphere for unforgettable moments.

Battery low message on mobile device screen. Internet and technology concept...

PC Laptops

9 Tips to Get More Power Out of Your Laptop Battery

Get more power out of your laptop battery and help it last longer by implementing some of these tips from our guide.

Users display warnings about the use of artificial intelligence (AI), access to malicious software ...

Les Olson

How to Stay Safe from Cybersecurity Threats

Read our tips for reading for how to respond to rising cybersecurity threats in 2023 and beyond to keep yourself and your company safe.

EXPLAINER: Tackling threat of mudslides in soaked California