Transcript Shoreline Formation - Wingate-Science

Shoreline Formation
• A. Shorelines are the natural boundary between
the land and ocean created by the action of
natural processes such as storms, tides, changing
sea levels, the outflow of materials from rivers,
and the work of plants and animals.
• B. Shorelines are due to powerful waves
constantly eroding rocks and depositing
sediments to reshape the land.
The following are examples of shoreline
formations:
1. Sea Cliffs- steep faces of rocks
2. Caves- hollowed out portions of sea cliffs
3. Sea Stacks- columns of resistant rocks left
standing
4. Sand Bars- an underwater ridge of sand
created by longshore currents
5. Beaches- waves deposit large amounts of rock particles
to form our beaches
a. The backshore is the area of the shoreline above the
high water or high tide mark. This can contain cliffs or
sand dunes or a berm (flat upper beach).
b. The foreshore is the area that is exposed at low tide. It
may have a beach scarp (vertical slope produced by
wave erosion) and a low tide terrace (broad flat area
exposed at low tide).
c. The offshore region extends from the low tide mark
seaward beyond the wave breaking zone. It has a
shoreface (slope below the low tide mark) and a
longshore trough (a depression parallel to the beach
between the low tide mark and wave breaking zone).
• 6. Barrier Islands- (nature’s way of straightening
out the shore) elongated bodies of sand
bounded on either end by inlets allowing salt
and fresh water to flow into and out of the
estuary behind the island. (Ex. Outer Banks)
The North Carolina’s Barrier IslandsThe Outer Banks
A. Barrier islands form in response to four factors:
1. A rising sea level- Melting of ice caps formed during ice
ages caused a change in sea levels beginning about 10,000
years ago. The sea level was 300 to 400 feet below its
present level. The following is an example of sea level
changes creating barrier islands.
– a. A straight coast forms during lower sea levels.
– b. Rising sea levels flood valleys on land and creates a sinuous
coast.
– c. Sand eroded from preexisting ridges forms spits (sandbar
connected to a curving shoreline)
– d. The spits are breached by storms, separating the islands from
the mainland.
2. A large supply of sand- 15,000 years ago the sea level
was much lower, waves and winds formed beach ridges
(dunes) on the coast of North Carolina. Sea levels rose
and broke through the dune forming a lagoon, and the
dune is now isolated as an island.
3. A gently sloping coastal plain- North Carolina’s coast
slopes at .2 feet per mile. The underlying geology of
North Carolina consists of sediments dating of
Quaternary age (1.8 million years ago to present) with
older sediments buried underneath. The deposition of
these sediments created a gentle slope conducive to
forming barrier islands.
4. Sufficient wave energy to move sand.
B. After barrier islands form, the islands then begin to
migrate landward in response to rising sea levels
(currently 1 foot per century).
1. Humans are increasing the rate of barrier island
migration through erosion by building structures to
prevent property damage. One example is seawalls.
Seawalls steepen the slope of the beach, which
increases wave size. This eventually leads to the loss of
beaches. (Four states, including North Carolina in 1985,
now prohibit shoreline armoring)
2. The Cape Hatteras lighthouse is evidence that
shorelines change over time and will continue to do so.
C. After World War II, the outer banks began to be heavily
developed leading to many problems and threats to
coastal residents.
1. Hurricanes and winter storms are a constant threat to
shore residents. The estimated property damage by
Hurricane Fran in 1996 is 4.1 billion dollars.
2. Pollution- Improper waste disposal, closing of fishing
grounds due to pollution, and drinking water
contamination after storms are just a few of the
problems in coastal North Carolina.
3. Environmental Destruction- The beaches of North
Carolina are being destroyed due to overdevelopment.
The Truths of the Shoreline
A. Beach erosion is an expected part of barrier island
evolution, especially as sea levels rise.
B. Shoreline erosion is not a problem until someone
builds a structure by which to measure it.
C. Shoreline erosion does not create problems for the
beach, it simply changes its position.
D. Human activities such as building seawalls, dune
construction, building construction, channel
dredging, reduce the beaches’ sand supply. This
increases the rate of shoreline retreat.
E. Shoreline engineering protects the interests
of few people, who are causing the erosion to
begin with, and is a high cost to state and
federal governments.
F. “You can have buildings, or you can have
beaches; in the long run you cannot have
both”. The ultimate truth is to avoid the
hazards and evaluate the level of risk if
choosing to build on a barrier island or
coastline.