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BARRIER ISLAND Fire Island, a barrier
island off the coast of Long Island,
New York, is about 51.5 kilometers long.
Sandbars may also form on coasts with straight shorelines. These bars
are not attached to the shore. Instead, they run parallel to it at some
distance offshore. They are called barrier islands. Barrier islands are found
along the eastern coast of the United States from New York to Texas. Some
well-known examples include Fire Island in New York, Atlantic City Beach
in New Jersey, and Hatteras in North Carolina. Galveston, Texas, and the
Florida cities of Palm Beach and Miami Beach are also located on barrier
islands. Padre Island, a barrier island in Texas, is notably long, measuring
about 160 kilometers from end to end.
Barrier islands, sandbars, and beaches are not permanent features.
The sand that composes them is constantly being removed by waves,
storms, and longshore drift. As long as the sand is replenished from rivers
or from other beaches, the feature persists. However, if the amount of sand
removed exceeds the amount replenished, then the feature erodes.
Types of Shorelines
Geologists have many ways to describe shorelines. One way to classify
shorelines is by whether they are regular or irregular. An irregular shoreline
is one with many inlets and bays. A regular shoreline is one that is relatively
straight. Whether a shoreline is irregular or regular depends in part on how
it was formed.
Irregular Shorelines
The coast of Maine, with its many inlets and bays, has an irregular
shoreline. Maine’s zigzagging shoreline, including the many offshore
islands, measures about 5565 kilometers. The actual coast of Maine,
however, extends over a distance of only 367 kilometers.
Most irregular shorelines appear to have formed when coastal areas
were flooded by the sea. This flooding occurred either because the land
sank or the sea rose, which the sea did at the end of the Ice Age. The coast
of Maine is thought to have formed when rising seas flooded hilly regions
cut by river valleys. As shown in the diagram at the top of page 353, the
drowned main valleys became short, deep, narrow bays. The divides
between the valleys became headlands. The drowned tributary valleys
became branches of the bays. Many hills were partly drowned and became
islands. Some were completely drowned and became shallow areas
called shoals.
The land along the Atlantic coast from New York to Florida is a coastal
plain. Much of this area also has an irregular shoreline formed by drowning
of the land. However, unlike the river valleys of Maine, those of the coastal
plain were wide and gently sloping. Thus, the bays of the coastal plain
are wider and longer than those in Maine. The water close to shore is not
as deep as in Maine, and there are fewer islands. Chesapeake Bay is
the drowned valley of the lower Susquehanna River and its tributaries.
New York Bay is the drowned valley of the lower Hudson River. Some
irregular shorelines were formed by glaciers. During the last ice age,
glaciers in Norway, Alaska, and other near-polar regions reached the
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Unit 4 Earth’s Changing Surface