SHIFTING SANDmore than meets the eye
PROCESSES
ACTIVE ON THE
BEACH
As you are lying on
Wrightsville Beach’s
strand, enjoying the
sun, there is a relaxing
background sound that
is constant in your ears
— rolling and crashing
waves.
Waves, generated
by faraway winds, are
the most noticeable
movement of water.
But there are other
important processes
active on the beach.
Other changes in water
level are associated with
storm surge, tides, and
sea level rise.
In addition to quartz, other minerals are
present in small amounts, including feldspar,
chert, mica and heavy minerals. The latter
are some of the most interesting elements on
the beach. These dark black to red minerals
are called heavy because their grain density is
greater than quartz. This greater density often
leads to their concentration along a zone on
the beach, such as at the high-tide line.
Look at your feet after walking on the
beach and you will see the quartz sand and
dark sand on them, too. Heavy minerals
are important for two reasons: First, they
help to determine the provenance or ori-gin
of the sediments as they indicate the
original “parent” rock of the sediments.
Compositional analyses indicate that most
of our beach sediments were originally
derived from Piedmont-zone igneous
(solidified from lava or magma) and meta-morphic
(transformed by heat, pressure,
or other natural occurrences) rock sources.
Although sand continues to move along the
beach, there is very little sediment currently
being added to the beach from our rivers or
along the Atlantic Coast.
Second, some of these heavy minerals
are valuable, and where concentrated in
large amounts, may be a mineable mineral
resource, as has occurred in Florida. Heavy
minerals, such as ilmenite, are a source of
titanium. Some of North Carolina’s beaches
were considered, but not used, for mineral
extraction during World War II.
Some of the shells are fossils or relict shells
that are derived from older rocks offshore
or from former shells that were part of the
marsh system behind the barrier. As the
island has eroded and moved landward, for-mer
salt marsh areas are now exposed on the
ocean side, revealing old marsh grasses and
oyster beds.
BEACH COMPOSITION
43
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