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Erosion caused by water

Southern California is world-renowned for its picturesque beaches, drawing in thousands from nearby and afar year after year.  Since the middle of the century, southern California beaches have been associated with a leisurely and glamorous lifestyle, and marketed as an ideal vacation destination.  If you live in California, chances are you have visited one of its beaches within the last year.  In many places, the coastline is dotted with expensive real estate, hotels, and restaurants.  Yet, in many of these places, the cliffs that these structures reside on, are crumbling into the sea.  Coastal erosion is the force driving the gradual breaking away of these cliffs.

Erosion is a natural process that shapes the world we live in.  It can create the foundation for our many environments, and change environments over time.  Erosion is best defined as the process by which soil and rock are removed from one place on the Earth’s surface and transported and deposited elsewhere.  The main drivers of erosion are wind, water, and ice.  That being said, however, human activities can increase the rate and severity of erosion, which can contribute to a host of environmental and economic problems.

Let’s take a look at some of the natural erosive forces:

Water: erosion by water results from rainfall, the currents of streams and rivers, the force of waves, and ocean currents.

Erosion caused by wind

Wind: erosion from wind occurs via two main mechanisms:

– deflation: when the wind picks up and carries loose soil particles

– abrasion: when surfaces are worn away from being struck by airborne particles

Ice: erosion from ice occurs via two main mechanisms:

– abrasion: when glaciers flow downhill over time, debris such as minerals and grains in the basal ice scrapes against the underlying rock, eroding away at it.

-freeze/thaw: when ice or snow melts, the water enters cracks in rocks, freezes again and expands, and breaks or fragments the rock.

Some of our most beautiful and striking scenery results from erosive forces.  Take Bryce Canyon in Utah for example.  Bryce Canyon is known for its curious “hoodoos” or rock spires.  Hoodoos are created by two different erosive forces: ice and water.  Hoodoos are composed of a layer of soft rock coated by a layer of harder rock.  When snow melts, water seeps into cracks in the hard outer layer, freezes at night, and expands the cracks in the rock, making may for more snowmelt to enter.  Eventually the softer inner layer is eroded away. Rainfall, being slightly acidic, dissolves the limestone on the outer layer, and gives the hoodoos their bumpy, bulging appearance.

Hoodoos in Bryce Canyon, UT, formed by wind and ice erosion

Now let’s look at some of the downsides of erosion.  In many coastal areas of California, ocean currents and the force of waves are eroding away at the coastal bluffs and cliffs.  Part of this is a natural process, and the chipping away of the cliffs helps replenish the underlying beach with sand.  However, human-induced factors such as global warming and resultant sea level rise are increasing the rate at which these cliffs erode away.  That spells out bad news for many of the seaside developments.

For the past fifty years or so, sea walls have been constructed in attempts to secure the shoreline and prevent it from eroding away.  Approximately ten percent of California’s 1,100 mile coastline is armored in some way.  This comes out to about 110 miles of seawalls or other protective structures.  Southern California is more heavily armored, with approximately one third of its coastline reinforced with some type of protective barrier.

The main goal of these structures is to protect human developments from falling into the sea, essentially.  While they are often successful in doing so, they exacerbate the problem as a whole by stripping the beaches below the cliffs, often making them narrower or causing them to disappear entirely.  Ultimately more money has to be poured into these projects to retrofit them in accordance with the changes in the geology that they in-part create.

Prime examples of areas where protective barriers have been installed:

Goleta Park Beach, north of Santa Barbara

-The segment of The Great Highway on the western edge of San Francisco

Solana Beach, northern San Diego County

San Clemente, southern Orange County

Construction of a sea wall in Solana Beach, CA. Photo via the Surfrider Foundation

Due to the California coast’s location on the boundary of two tectonic plates, most of its  beaches are naturally very narrow and rocky.  This area is a subduction zone – an area where two plates collide and one subducts, or submerges under the other.  This results in a rocky, abrupt and narrow coastline with little beach area.  Those postcard-worthy, sprawling sandy beaches dotted with umbrellas and coolers are a human-creation in southern California.  Many beaches in Southern California have sand imported from elsewhere to compensate for erosion and the natural geologic makeup of those beaches.

A natural narrow and rocky beach in California

A natural shifting sand cycle exists on the coasts of Southern California.  During winter and springtime, powerful storm surges pull sand from the shore and transport it out to sea.  Over summer months the currents are calmer and sand is deposited back on the beach.  It is natural to visit the same beach and see a scarce beach area over winter and a much more ample one in summer.

Sometimes you just can’t fight nature.  Several states and towns in the U.S. have adopted policies of retreat from receding coastal areas.  Just south of San Francisco, the town of Pacifica, for example, has purchased several seafront properties and subsequently demolished them.  Several Atlantic states, such as New Jersey and Delaware, have implemented “no-build” areas under the National Coastal Zone Management Program.  New developments are prohibited in these areas.  California as a state, however, does regulate coastal development to a certain extent, but has not identified shorefront “no-build” areas.

Exacerbated erosion doesn’t just happen on the coast.  In fact, erosion is a major and widespread problem throughout many inland areas on multiple continents.  One of the major contributors to the increasing rate of erosion is large-scale agriculture.  Upon clearing of natural vegetation to make way for crops, the fertile topsoil is often blown away by wind or washed away by rain.  In many cases, after time, the quality of the soil deteriorates to the point that the land can no longer be cultivated and must be abandoned.  Cultivation shifts to new, more productive sites, which eventually become degraded and abandoned as well.  It is estimated that one third of the world’s arable land has been lost through erosion and other degradation since 1960.

Additionally, soil carried away by rainfall or irrigation water has to end up somewhere, and often leads to sedimentation, or the depositing and settling of particles , in rivers, lakes and coastal areas.  Sedimentation can negatively affect the ecological communities of these areas by changing the course of waterways and otherwise altering the natural structure of the ecosystem.  Furthermore, pesticides and fertilizers employed by large-scale, commercial agriculture get transported by rainwater and irrigation runoff, and often pollute waterways and cause substantial harm to plants and wildlife.

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