several means as part ofweathering and mass wasting. Ice along shorelines is
capable of considerable leverage in prying apart rocks.
Movement of materials along the shoreline is quite obvious by close observation.
Sand moves in rhythm shoreward and seaward with the break and ebb of the waves.
These distances are, at best, a few meters. There is considerable work that is performed
by the abrasion of small rock and sand pieces one against the other; they are lessened
in mass and smoothed. On closer examination, sand and other small materials exhibit
“odd” behavior as waves break along the shoreline. A small portion of the breaking
wave water is absorbed into the wet beach while most of the broken wave flows down
the beach slope in the direction of the ocean. Although this might seem obvious, the
net motion of materials suspended in the waves is not. Usually, waves approach the
shoreline from a direction other than straight on to the beach slope. While the local
beach has a single slope direction, the wind can push waves from various directions,
which breaks waves onto a beach from directions other than that of the slope. The sus-
pended materials travel with the waves onto the beach from the direction from which
the waves originate. The water that has broken onto the beach travels directly down
the beach slope via gravity. The motion is a zigzag transport of materials causing net
transport in parallel to the shoreline, which is known as beach drifting. Some of these
materials are picked up in longshore currents and can be transported great distances.
The beach is a depositional form. Erosion is prominent along coasts but beaches
are, perhaps, the most obvious coastal landform. They represent depositional mate-
rials in “temporary storage” until such time as the materials can be re-suspended. As
such, they are continuously being built and/or eroded by water. Tides have surpris-
ingly little net landscaping influence on beaches and are greatly overshadowed by
events such as storms or tsunamis or long-term rise and fall of sea level.
Beach sand is not always white and varies considerably in color, including reds
and blacks, as the result of the erosion of volcanic rocks. Though very common,
sand is not the only size material found along shorelines. Cobbles, rocks, pebbles,
silts, and clays comprise beach along various coastlines and their occurrences are
dictated by the particular combination of eroded materials and energy of the water
action at each location. In areas with plentiful shoreline sand and enough wind, dry
sand can be suspended in the air and moved inland. Progressive wind erosion of
the beach sand causes dunes inland. Some coastal dunes rise many tens of meters
and their presence is a protection against higher water levels in major storms.
There are numerous other depositional forms. When sand piles on the sea bottom
offshore it is known as an offshore bar. Sometimes, offshore bars are deposited
above sea level and become barrier islands. The Gulf and southern Atlantic coasts
of the United States are flanked by thousands of kilometers of barrier islands with
shallow, protected lagoons lying between them and the mainland. As longshore
currents encounter embayments there is the tendency for them to slow and drop68 Coastal Erosion and Deposition