by For more than a century, the Great Flood of 1862 remains among California’s worst natural disasters – a megawatt storm that has been used as a benchmark for state emergency planners and officials to better prepare for the future.
A frightening repeat of the flooding – which killed at least 4,000 people and turned the Central Valley into a 300-mile-long sea – would likely dwarf the devastation of a major earthquake in California and cause up to $1 trillion in damage, some say experts.
But even as California struggles to cope with the whiplash effects of climate and increasingly extreme weather, new research suggests the potential scale of those events could be far greater than the 1862 deluge.
After analyzing sediment layers at Carrizo Plain National Monument, researchers at Cal State Fullerton say they have identified two unrecorded massive flooding events in Southern California in the past 600 years.
Remarkably, their analysis suggests that the floods were much larger than the Great Flood, which reshaped much of the Central Valley and the Los Angeles Basin.
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Researchers based their conclusions on multiple core samples taken from a so-called “sag pond” along San Andreas Pond, in the southeast corner of San Luis Obispo County. Analysis of the core samples revealed signs of two epic floods — one occurring sometime between 1470 and 1640 and the other between 1740 and 1800.
What they couldn’t find in the core samples, however, was a sign of the Great Flood, suggesting it may have been much less consequential than the other two.
“We’re not looking at the geological signature of what’s supposed to be the biggest event in historical time, and what we’re basically using as the basis for a lot of the models and predictions about future floods,” said Matthew Kirby, professor of geology. at Cal State Fullerton and lead author of the study.
“That’s a concern for us because I think we’re probably underestimating the amount of naturally occurring flooding, and that’s something we really need to understand.”
The findings, recently published in the Journal of Paleolimnology, add to a growing body of research that suggests Californians may be unaware of how devastating future floods can be. If such major floods have always been part of California’s natural cycle of drought and flooding, how much worse could they be in an era of climate change?
“We look back at our history, and these massive events come to us, and they’re going to continue,” said Josh Willis, a climate scientist at NASA’s Jet Propulsion Laboratory in La Canada Flintridge, who was not involved in the research. “But global warming will almost always make them worse. So, the wild ride will get worse.”
Willis said it was “fascinating” that there was no trace of the 1862 flood in the geological record.
“It begs the question, ‘Why wasn’t that one in the core of the sediment?’ And if the answer is, well, it wasn’t big enough, … then that’s kind of scary for the future,” Willis said.
However, he warned against drawing too many conclusions from a single paleoclimate study, saying that it “paints a small part of the picture.” Willis noted that both of these major flood events from ancient times occurred during a period of global cooling known as the Little Ice Age, which lasted from about the 14th to the 19th century.
“We are looking 1717369992 at a climate that’s not colder, it’s going to be warmer,” Willis said. “We’re warming the planet, so maybe comparing it to the Little Ice Age isn’t the best analog.”
But he said it could also indicate that future floods could be worse than in the past, since the atmosphere has the ability to hold more water in a warmer climate. He said these are questions that need more research, and can continue to build on the sag pond results.
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Tessa Hill, professor of Earth and planetary sciences at UC Davis and director of the university’s Ocean Climate Lab, said the study contributed to a more complete understanding of past flood events.
“Previous work in this regard has relied mainly on coastal sediment records, which can record very accurate and high-resolution climate records but may not reflect the complexity of what is happening in different regions of California,” said Hill , who was also not involved. in the research.
“It is critical to predict the consequences of a changing climate for California residents,” she said.
Paleolimnology, the study of ancient lakes, is one way researchers are trying to better understand California’s history. But Southern California doesn’t have many natural lakes, and many of the ones that do exist are located high in the mountains — not the best location for researchers looking for clues about past floods.
Instead, Kirby and his team turned to sag ponds, or land depressions along active fault lines that often accumulate water.
“Saga ponds may be a valuable and generally underutilized paleo-archive,” the study authors wrote.
At Plain Carrizo National Monument, the researchers took five core samples from a pond that is now dry. The core samples, each 4 to 5 feet long, contained many layers of sediment – clay and biological material that had been washed into the lake from the surrounding hills and shores and settled to the bottom.
Changes in the type and size of the sediment indicated that energy was required to erode and deposit it in the basin — the larger the grain, the more energy required. Kirby said the team helped piece together the two separate flood events – one from 380 to 554 years ago, and the other from 284 to 224 years ago.
Kirby said the 1862 flood probably left a geological footprint in the core, but it was not scientifically significant, especially compared to the two ancient floods.
“It doesn’t show up in the geological archives as you might expect, considering its size,” Kirby said. “Not like [the flood] it didn’t happen, of course it happened. It was huge. But … as we dig deeper into the geological record for the last 11,700 years, … we are able to show, without question, that there is a lot that is happening that we have not seen during historical time.”
The 1862 flood was used as a key data point to create the “ARkStorm Scenario,” which was originally projected as a once-in-a-thousand-year catastrophic flood event in California, but now some scientists say it may not be that big.
“Potential flooding in California in the future could be worse than recent flooding,” said Samuel Hippard, a Cal State Fullerton student and one of the study’s co-authors, in statement. millions of Californians.”
Another recent study found that there has been much more atmospheric river activity in the past 3,000 years than previously, which also indicates that California officials may have underestimated rainfall and flooding in the past. .
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Kirby said he hopes to continue to focus his work in this area, looking to document more historic floods from core lakes and ponds.
“It was very exciting to find that we were able to extract paleo storm events from this tiny lake,” Kirby said. “There aren’t many lakes in California, especially in Southern California, … so it’s really helpful for us to find an archive where we can get additional information.”
Kirby has identified at least three other sag ponds in Southern California for potential future research, and several more in the Central Valley and Northern California.
“Scientists know very little about California’s flood history older than the historical record of the last 150 years,” said Kirby, who has been studying Earth’s climate history for years. “If these sag pools become an archive where we can explore and find these individual events, it will really advance our science and our understanding of the history, frequency and magnitude of past floods .”
This story originally appeared in the Los Angeles Times.
