An accumulation of sediment exposed to wave
action along a coastline. The beach extends from the limit of
the low-tide line to the point inland where the vegetation and
landforms change to that typical of the surrounding region.
Many beaches merge imperceptibly with grasslands and
forests, whereas others end abruptly at cliffs or other permanent
features. Beaches may occupy bays between headlands,
form elongate strips attached (or detached, in the cases of
barrier islands) to the mainland, or form spits that project
out into the water. Beaches are very dynamic environments
and are always changing, with material being eroded and
redeposited constantly from day to day and from season to
season. Beaches are typically eroded to thin strips by strong
winter storms, and built up considerably during summer,
when storms tend to be less intense. The processes controlling
this seasonal change are related to the relative amounts of
energy in summer and winter storms—summer storms
(except for hurricanes) tend to have less energy than winter
storms, so they have waves with relatively short wavelengths
and heights. These waves gradually push the offshore sands
up to the beach face, building the beach throughout the summer.
In contrast, winter storms have more energy with longer
wavelength, higher amplitude waves. These large waves
break on the beach, erode the beach face, and carry the sand
seaward, depositing it offshore.
Some beaches are bordered by steep cliffs, many of
which are experiencing active erosion. The erosion is a function
of waves undercutting the base of the cliffs and oversteepening
the slopes, which attempt to recover to the angle
of repose by rainwater erosion or slumping from the top of
the cliff. This erosion can be dramatic, with many tens of feet
removed during single storms. The material that is eroded
from the cliffs replenishes the beaches, and without the erosion
the beaches would not exist. Coarser materials are left
behind as they cannot be transported by the waves or tidal
currents, and these typically form a rocky beach with a relatively
flat platform known as a wave-cut terrace.
Lagoons, bays, and sounds separate the mainland from
barrier islands that are long narrow offshore beaches. Barrier
islands are common along the east coast of the United States
(e.g., south shore of Long Island; Atlantic City, New Jersey;
Outer Banks of North Carolina; and Galveston, Texas).
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