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El Niño beach erosion previews global warming impacts

USGS finds 2009 – 2010 storms caused unprecedented coastal erosion

A series of photos showing coastal erosion at San Francisco's Ocean Beach. PHOTOS BY PATRICK BARNARD, USGS.

By Summit Voice

SUMMIT COUNTY — Winter shoreline erosion at San Francisco’s Ocean Beach of more than 180 feet during the El Niño storms of 2009 – 2010 may be a harbinger of future climate change impacts, geologists said after an extensive West Coast assessment covering the shoreline between San Diego and Seattle. The researchs looked at up to 13 years of seasonal beach survey data along 148 miles of coastline to track shoreline changes through a range of wave conditions.

“The stormy conditions of the 2009–10 El Niño winter eroded the beaches to often unprecedented levels at sites throughout California and vulnerable sites in the Pacific Northwest,” said Patrick Barnard, a coastal geologist with the United States Geological Survey in Santa Cruz, Calif.

In California, for example, winter wave energy was 20 percent above average for the years dating back to 1997, resulting in shoreline erosion that exceeded the average by 36 percent, Barnard and his colleagues found.

Getting a better understanding of how the 2009–10 conditions tore away and reshaped shorelines will help coastal experts better predict future changes that may be in store for the Pacific coast, the researchers said.

Barnard’s team published their findings in the July 9 issue of Geophysical Research Letters, a journal of the American Geophysical Union.

The Ocean Beach erosion resulted in the collapse of one lane of a major roadway and led to a $5 million emergency remediation project. In the Pacific Northwest, the regional impacts were moderate, but the southerly shift in storm tracks, typical of El Niño winters, resulted in severe local wave impacts to the north-of-harbor mouths and tidal inlets. For example, north of the entrance to Willapa Bay along the Washington coast, 345 ft of shoreline erosion during 2009 – 2010 destroyed a road.

The beach erosion observed throughout the U.S. West Coast during the 2009–10 El Niño is linked to the El Niño Modoki (‘pseudo’ El Niño) phenomenon, where the warmer sea surface temperature is focused in the central equatorial Pacific (as opposed to the eastern Pacific during a classic El Niño).

As a result of these conditions, the winter of 2009 -2010 was characterized by above-average wave energy and ocean water levels along much of the West Coast, conditions not seen since the previous major El Niño in 1997 -1998, which contributed to the observed patterns of beach and inlet erosion.

Many climate change models predict ever-warmer waters in the central Pacific, so El Niño Modoki is projected to become a more dominant climate signal. When combined with still higher sea levels expected due to global warming, and potentially even stronger winter storms, these factors are likely to contribute to increased rates of beach and bluff erosion along much of the U.S. West Coast, producing regional, large-scale coastal changes.

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9 Responses

  1. This process has been going on since the melting of the ;last ice age, especially when the Pacific Ocean was way off the coast, perhaps to where the continental shelf falls off into the depths. This always happens when there is a severe Winter on the West Coast, though it seems will become more frequent as time goes on. Indeed, if the Oceans rise due to the melting of the ice caps and glaciers, the we can expect to see more of the same.

  2. Bob:

    Your report was lacking a lot information.
    1. Was the fault that runs under this area more active that normal.
    2. How much has sea level risen in this area in the last few years.
    3. Did the area have unusually high rain fall at that time.
    4. You mention a major roadway. If your talking about the “Great HWY”,
    this road is only about five miles long.

    A little more work might give you some credibility Bob.

  3. I believe the photos are of highway 1 in Pacifica, @ devils slide. This area has been a trouble spot over the years every winter, especially when the rains & surf are heavy. Erosion of the beach/cliffs are common during this time. It has nothing to do with the fault. As far as the story goes, I can see that there wasn’t the correlation about the great highway turning into highway 1 further down the road. As for credibility, the same can be said of what David asks.

    • Norman, the pics are definitely from Ocean Beach, right in San Francisco. I lived in Montara, right down the road from Devils Slide, for several years.

      As far as the story, I think the overall point is that many climate models suggest that the mid-Pacific-type El Niño will become more persistent, and that could lead to more of the type of storms that result in coastal erosion. Clearly, there are other factors that can also lead to more coastal erosion, as suggested by David.

      Neither the USGS authors or myself are suggesting that this particular El Niño storm cycle was directly related to global warming. I think the story clearly says that the erosion seen during the 2009-2010 winter may be a sign of things to come under certain global warming scenarios.

  4. Sorry Bob, no cigar. Actually, Devils slide is between Pacifica & Montara on highway 1. The Great Highway veers in towards Lake Merced, joining Highway 35, Skyline Blvd, which joins Highway 1 along the coast as it then veers inland running along the ridge. But, that said, one can say in a sense, that it’s all coast highway, still being correct.

  5. Yes Bob, but the pics shown as well as the history is of Devi;s slide. It effectively blocked getting to/from Montara, as the only way was to come up from the south. It took awhile, but they built a new road overland to tie in well away from the edge. Also over to the Skyline Blvd I believe. The cause of the slide was indeed erosion The whole area is prove to falling into the Pacific Ocean each year, but really does so when the surfs up. The State just got tired of repairing it along it’s present route.

  6. One other point, the beach is flat along the great highway, except for when it drops down from Geary Blvd @ the Cliff House. But, I won’t argue with you, because this is your blog.

  7. That’s what separates the men from the boys Bob, you are indeed one of a kind.

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