Great question! And a complicated one!
Beaches form as the result of waves or water
currents moving and depositing sand and other
loose sediments along the shoreline. Beach erosion
happens by the same process, but instead of sand
being deposited it is carried offshore. Therefore,
the movement of ocean water is what causes the
sand transportation and thus beach formation along
the coasts. And the waters in the ocean are
always moving! That water movement is due to a
variety of factors including, Earth's rotation,
gravity, wind patterns, temperature and salinity
(saltiness) of the water, the shape of the sea
floor, and the presence of land masses (such as
the Channel Islands).
The Goleta coastline happens to be where
several ocean currents converge, or meet and flow
together. The California Current flows south,
bringing cold Alaskan waters down along the coast.
The Southern California Counter-current brings
warm waters up the coast from Baja California.
There is also warm, saline (or salty) waters
brought into the coast from the central North
Pacific Ocean from regular tide movements. Off of
our coastline, there is also coastal
upwelling of nutrient rich waters from the
deep ocean. Upwelling is caused by the blowing
of wind along the coast, causing surface
waters to push away from the coast, which allows
the cold, nutrient-rich waters from the bottom of
the ocean flow up and replace the surface waters
being pushed out to sea. This combination of
currents forms one of the most biologically
productive ecosystems along the U.S. coastlines.
And as these water bodies converge off the coast,
they wrap back around to the south (imagine the
water converging near Point Conception and flowing
around counter-clockwise back into the Los Angeles
coastline) due to the coastline shape. As they
converge, both the south-flowing and north-flowing
waters split and flow around the Channel Islands.
This causes a variety of differences in the ocean
movements within the Santa Barbara Channel, which
does affect the Goleta coastline. I am not a
coastal geology expert, so that is about all I can
say. But I do know that the Channel is
relatively protected compared to the oceanward
side of the Channel Islands, meaning that the
islands act as a wave blocker. Without
the Islands, our shoreline may have less sandy
beaches because the waves (especially storm waves)
would wash away all the sand.
An equally important factor to consider when
thinking about why we have beaches and where they
form, is human development. Humans are huge
factors of beach erosion by changing the coastline
or building artificial barriers to the natural
ocean erosion. For example, the airport in
Goleta is located where there used to be a swampy
lagoon , similar to the Devereux Slough that
was recently restored near the Ellwood Bluffs.
When humans closed off the lagoon, they also
closed off a sediment source into the oceans.
Another example is the break wall in the Santa
Barbara harbor. The seawall protects the coast
from erosion, but it also disrupts the natural
transportation of sediments along the coast.
The end result is that it causes increased erosion
down drift from the sea wall, meaning it causes
beaches to be stripped of their sand. To
counter the effects of sea walls, several beaches
along the Goleta coastline have massive amounts of
sand dumped onto them. You may have seen Goleta
Beach under construction in the past as every year
engineers try to add large stone blocks along the
coast, that are then buried under sand, to prevent
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