Shifting sands and changing tides bring unstable bluffs

I don’t remember when I first became aware that the beach was not a stable place. It must have been during my first full winter as a surfer, when I ran toward the sand, only to find much of it had slipped away. It would take an entire season before I saw the sand reappear, as mysteriously as it had disappeared.

I didn’t yet realize that in our region, the north swells of winter swept the sand into the deep-water canyons to the south and that the south swells of summer brought them back again. Then came one of our biggest winters on record as the waves of 1983 stripped sand from the beaches and didn’t return it for another two decades.

With the cliff’s base hollowed out, there is no foundation for the rest of the cliff and bluff failure is only a matter of time. Photo by Chris Ahrens

It was my friend, marine geologist, oceanographer and ocean science researcher Gerry Kuhn who helped make sense of it all. In the mid 1980s, Kuhn, along with the late Francis Shepard, Scripps’ Institute professor emeritus and the “father of marine geology,” wrote a book called “Sea Cliffs, Beaches and Coastal Valleys of San Diego County.” The subtitle of the book, “Some Amazing Histories and Some Horrifying Implications” tells a great deal about the book’s contents.

Kuhn’s classic book documents coastal erosion in words and photos, showing various bluff failures in our area over the years, along with the changing face of our local beaches. The following is a paraphrase of some of the wisdom I gleaned from Kuhn and his book over the years.

Currents change over the years and beach sand shifts with those changes. Beach cobbles are river rocks swept out to sea during heavy rains, where they are buried offshore, in the sand. When the sand is washed from the reefs, the cobbles have no resistance and roll up on the reef and deposit themselves on shore. When large amounts of sand have been washed off the beach, the cliffs are left without a barrier against the cobbles. A one-two punch occurs as the cobbles slam the cliff’s base, eating away the sandstone like millions of little teeth. With the cliff’s base hollowed out, there is no foundation for the rest of the cliff and bluff failure is only a matter of time. Before long, the cycle repeats, on and on, until the cliffs retreat with sometimes tragic consequences, as happened when the Self Realization Temple fell into the ocean in the early 1940, apparently caused by ground saturation from a series of violent storms. (A recent bluff failure directly below Self Realization Fellowship occurred at nearly the same spot where the old temple fell.)

But heavy storms also protect the cliffs. When the rivers flood, they nourish the beaches with new sand. Since the restoration of the river mouths at Ponto and Del Mar, sand is again pouring back onto North County’s beaches. As a result, there is more sand now than there has been for decades. And more sand means better beach breaks for surfers. Better beach breaks means the crowds spread out more and all of us enjoy more waves.

To learn more about beach erosion or order a copy of Gerry Kuhn’s enlightening book, visit amazon.com/Cliffs-Beaches-Coastal-Valleys-County/dp/0520074335.

 

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  1. Gerry Kuhn says:

    Hi Chris,
    This is the first time I saw this!
    Very nice writeup!
    Thank You!
    Gerry

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