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Lake Los Carneros

Paul Wellman

Lake Los Carneros


Searching for 200-Year Storms

Scientists Scour Santa Barbara Lakes for Evidence of Floods, Landslides


Thursday, September 6, 2012

Though Californians usually worry about when The Big One will swallow us into the earth, a statewide disaster is more likely to fall from the skies, as prolonged, powerful storms have proved much more cataclysmic than earthquakes over the centuries. Take the Great Flood of 1862, when roughly 40 days and 40 nights of steady rain drowned the entire Central Valley, made lakes of Los Angeles and Orange counties, forced citizens to abandon Ventura, silted in the Goleta Slough, swamped Santa Barbara from Garden to Milpas streets, and bankrupted the state.

Future floods could be even worse: Experts fear we are overdue for an even stronger deluge, one that could cost the state more than $700 billion, force the evacuation of 1.5 million people, and harm more than a quarter of California’s buildings. Scientists call this theoretical tempest an “ARkStorm,” which is a nod both to Noah’s mythical Ark and to the “Atmospheric River” of West Coast–aimed tropical moisture that would fuel such a downpour, an effect formerly known as the “Pineapple Express.” While the strongest evidence of previous ARkStorms comes from underwater geologic records just off the coast of Santa Barbara, scientists are now scouring lakes in the area for a better idea of when it’ll be time to batten down the hatches once again.

Kevin Schmidt of the U.S. Geological Survey holds Lake Los Carneros core samples.
Click to enlarge photo

Paul Wellman

Kevin Schmidt of the U.S. Geological Survey holds Lake Los Carneros core samples.

“We’ve set out to find an onshore record of these big storms,” explained Kevin Schmidt, of the U.S. Geological Survey, which is now comparing evidence pulled from lake bottoms to what’s been found on the nearby seafloor, where large “pulses” of sediment suggest floods and/or landslides every 200 or so years. “The big question is, how often do they happen?”

Unlocking that mystery is Project Bigfoot (as in “Big” Storm “Foot”-print), a Menlo Park–based USGS team of scientists with complementary skill sets, including Schmidt, whose background is in geomorphology and quaternary mapping, and Dave Wahl, an expert at paleoenvironmental reconstruction. “We have this broad suite of tools we can each bring to the table in terms of our ability to answer questions,” explained Wahl, and Santa Barbara’s unique geography and geology make it one of the few places on the West Coast where this evaluation is even possible. “The types of environment I need to do this paleo work are very few and far between in coastal California,” said Wahl.

A couple of weeks ago, Wahl and Schmidt could be found floating in an inflatable catamaran atop Lake Los Carneros in Goleta, where they pulled six-foot sediment cores out of the lake in a man-powered methodology that Schmidt called “relatively inexpensive.” The team is also referencing evidence from Vandenberg, Pt. Mugu, Santa Rosa Island, and Zaca Lake, with hopes of accessing Hope Ranch’s Laguna Blanca soon. Once in the lab, the team will use a “multiproxy approach” to date the sediment layers, examining magnetic signatures, radiocarbon evidence, and even pollen markers, as age can be determined based on whether remnants of native or introduced European grasses exist in the cores.

The onshore dates will be compared to offshore data collected by Indiana University’s Arndt Schimmelmann, whose 2006 announcement that major floods occurred every 200 or so years has recently been fine-tuned by his colleague, Ingrid Hendy of the University of Michigan. “Our work is a story of floods and droughts,” wrote Hendy in an email, explaining that the 200-year floods occurred regularly for the past 2,000-plus years, except during a dry period between 800 and 1200 ce, when droughts lasting 10 to 50 years dominated. Though such a drought would probably cripple the economy today, the more frightening part is that the 1862 storm produced only four millimeters of sediment, while earlier floods in 1530 and 1270 ce generated flood layers five centimeters thick, 10 times the size of the state’s so-called Great Flood. Given that California hasn’t experienced that intense weather since the Middle Ages, Schimmelman explained that such a flood is “statistically overdue.”

USGS scientists take core samples from Lake Los Carneros.
Click to enlarge photo

Paul Wellman

USGS scientists take core samples from Lake Los Carneros.

Though Project Bigfoot’s results won’t be complete for at least nine months, the ramifications will be both broadly regional ​— ​in that the entire West Coast can become better prepared for the timing of a superstorm ​— ​and hyper-local, in that the Santa Barbara area will learn more about acute landslide and flooding threats. “With any of this work where we’re looking back in time,” explained Wahl, “the ultimate goal is to turn and look forward in time, and have a better understanding of what might be happening in the future.” That may translate to more thorough emergency preparation and better informed civic planning, among many possible manifestations.

Up at the Santa Ynez Valley’s Zaca Lake, where a distinct but overlapping study has been underway since 2009, researchers were able to pull out nine meters of sediment core, giving them a look back at 3,000 years of history. “Zaca is really special,” said Sarah Feakins, from the University of Southern California, explaining that the lake gets a lot of annual sediment that’s very well preserved. “The lake is so productive.” Since the modern understanding of weather patterns is sporadic and, at least on a geologic time scale, very short-sighted, Feakins explained, “These lakes allow us to go back further.”

Aside from debunking the oft-repeated legend that Zaca Lake has no bottom ​— ​Feakins’s team took samples from all corners of the lake, finding it to be about 12 meters deep ​— ​her research may determine that large flood events came after droughts and/or wildfires rather than during consistent wet periods. Additionally, she expects to learn information about smaller storms that did not create the massive sediment flows required to reach the ocean floor. Whatever the results, the published research is anxiously awaited. “We don’t have that much to compare it to,” said Feakins, who expects some data to come out by the end of the year. “It’s all new news.”

Back in Goleta, Wahl is even excited about the secondary information his team will get about the landscape’s evolution over time, such as when these lakes were first modified by man and when European grasses started to proliferate. “Those results will be there along with what we’re looking at,” he explained. “You get to tell the story of the lake along with the specific research questions.”

But, at least for starters, just finding evidence of the 1862 flood in Lake Los Carneros would make the scientists smile. “We’re hoping we can see a record of that guy,” said Schmidt. “There have been more recent big winters, but they pale in comparison to that one.”

Of course, you can keep worrying about The Big One, too, because if a sizable earthquake comes when California’s soils are saturated by the next ARkStorm, you can expect the ensuing landslides and related catastrophe to be exponentially worse.

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