CGS Geologists Assess Multiple Fire Burn Areas for Landslide Potential: 10-1-20 Update

Wildfires are a disaster that can spawn yet another disaster.

Fire eliminates ground covering on slopes, exposing the soil underneath and making it more susceptible to debris flows. Such events can be catastrophic, as was the case in Montecito (Santa Barbara County) in 2018.

David Longstreth, senior engineering geologist in California Geological Survey’s (CGS) Forest and Watershed Geology program, is one of many in the field studying burn areas in the Santa Cruz area after the SCU Lightning Complex. He is determining risk communities can expect come rainy season.  

According to Longstreth, concerns point to “the Highway 9 corridor through Boulder Creek starting approximately near the Brookdale area.” 

Preparing for this hazard, CGS scientists continue to deploy as part of cross agency Watershed Emergency Response Teams (WERTs) studying the damage of wildfires and determining the risk of debris flow, such as mudslides.

Led by the California Department of Forestry and Fire Protection (CAL FIRE) and co-led by CGS, WERTs help communities prepare after wildfire by rapidly documenting and communicating post-fire risks to life and property posed by debris flow, flood, and rock fall hazards.

A new CGS webpage, Recent Landslide Hazard Assessments, is now live to share CGS’ ongoing, on-the-ground assessments of several ongoing wildfires across the state.

The new CGS page updates with our post-wildfire watershed emergency response info for several fires.

You can also follow DOC’s Landslide Hazard Watch Twitter collection for the latest geology-related updates to the state’s wildfire response, including this CAL FIRE interview, again with Longstreth on the CZU Lightning Complex burn area:

In early August, CGS and CAL FIRE assigned a WERT to the Apple Fire in Riverside and San Bernardino counties to assess such a threat.

One tool the team uses is a helicopter to survey the damage caused by the burn and determine the potential debris flows risks to nearby neighborhoods, roadways, and waterways.

Two California Geological Survey staff take a photo before boarding a helicopter to complete a post fire analysis of the Apple Fire.
CGS engineering geologist Kevin Doherty and Cheyenne Borello of CAL FIRE’s San Bernardino Unit prepare to board a helicopter to view potential landslide hazards in areas in Riverside and San Bernardino counties burned by the Apple Fire. CGS senior engineering geologist John Oswald snapped the photo before climbing aboard himself.

CGS’ Apple Fire WERT team consisted of Kevin Doherty (Engineering Geologist – Santa Rosa) and John Oswald (Senior Engineering Geologist – Eureka), who completed field assessments while Sol McCrea and Pete Roffers (Engineering Geologists – Sacramento) worked continuously from home developing and compiling GIS data for the team.

CGS also coordinated with CAL FIRE, CAL FIRE’s Watershed Program, and the US Forest Service Burned Area Emergency Response (BAER) Team in the assessment.

Per WERT protocols, no hazard data is released until after all relevant information has been compiled, analyzed, and explained to local and state agencies.  Official communication is ultimately reported to the public by CAL FIRE.

As of early September CGS was also deployed to the River and Carmel fires in Monterey County, the LNU fire in Sonoma, Napa, Solano, and Yolo Counties, the CZU fire in Santa Cruz and San Mateo Counties, the SCU fire in Stanislaus, Alameda, and Contra Costa Counties.  On September 18 staff deployed to the El Dorado Fire in San Bernardino and Riverside Counties. 

CGS on the Saddle Ridge Fire — October 2019

In October of last year, CGS Engineering Geologist Sara Gallagher (Eureka) deployed to the site of the Saddle Ridge Fire to assess the potential for future landslides on the burned slopes of Los Angeles.

And, in 2017, CGS received a prestigious award from CAL FIRE for its post-fire debris flow analysis on the Thomas Fire in Santa Barbara County.

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