For most people, when they think of coastal areas they picture a beach, and the beach that they imagine is probably a typical sandy beach composed of sand grains (section 12.2). But beaches are comprised of whatever types of are dominant in the local area. For example, parts of Hawaii and Iceland are famous for their black sand beaches, made up of eroded and other volcanic materials. The beautiful tropical white sand beaches we see in travel ads are largely composed of the crushed calcium carbonate remains of coral skeletons (much of which has been chewed up and excreted by a fish before we happily run our toes through it!) Other beaches may lack sand altogether and instead be dominated by small shells, or larger rocks or pebbles (Figure 13.1.1).
The shoreline is divided up into multiple zones (Figure 13.1.2). The is the region of the beach above the high tide line, which is only submerged under unusually high wave conditions, such as during storms. The lies between the high tide and low tide lines; it is submerged during high tide and is exposed during low tide. The extends from the low tide line to the depth where wave action is no longer influenced by the bottom, i.e. to where the depth exceeds the (section 10.1). Finally, the zone represents the depths beyond the nearshore region.
Along the beach itself, the area above the high tide line is called the , which is usually dry and relatively flat. The berm often ends with a berm crest or berm , which is a steeper wall carved out by wave action that leads down to the foreshore. The foreshore has a number of other names, including the , the or , and if the area is fairly flat, the . Just off shore from the beach there are often and longshore troughs running parallel to the beach. The longshore bars are accumulations of sand that are deposited by wave action and (section 13.2). The decrease in depth above longshore bars is what often causes waves to start to break well before reaching the beach (section 10.3).
The sand or other particles that make up the beach are distributed by wave action. The water that moves over a beach through incoming waves is called , and it also contains suspended sand grains that can get deposited on the beach. Some of the swash percolates into the sand while the rest of the water washes back out as as the wave recedes. Backwash removes sand from the beach and returns it to the ocean. Sand will therefore be deposited or eroded depending on which process is dominant. If wave action is light, a lot of incoming water gets absorbed by the sand, so swash dominates. Under heavier waves the beach becomes saturated with water, so less can be absorbed, and backwash is dominant. This leads to seasonal cycles in beach structure; waves are heavier during the winter as a result of stormier conditions at sea, so backwash dominates and sand is removed from the beach and deposited offshore in . In the summer the waves are gentler, swash dominates, and the sand is transported from the longshore bar and deposited on the shore to create a wider, sandy beach (Figure 13.1.3).
a mineral composed of silicon and oxygen atoms in the ratio of 1 Si:2 O; one of the most abundant minerals in the Earth's surface (12.1)
unconsolidated particles of mineral or rock that settle to the seafloor (12.1)
a volcanic rock that makes up much of the oceanic crust (3.2)
the region of the beach above the high tide line, which is only submerged under unusually high wave conditions (13.1)
the part of a beach between the high tide and low tide lines (13.1)
the part of a beach from the low tide line to the depth where wave action is no longer influenced by the bottom, i.e. to where the depth exceeds the wave base (13.1)
the depth of water that is affected by the sub-surface orbital motion of wave action (approximately one-half of the wavelength) (10.1)
the beach zone beyond the nearshore region (13.1)
a flat area of a beach in the backshore area (above the high tide level) (13.1)
a short, steep wall carved out by wave action between the foreshore and the berm of a beach (13.1)
the area of a beach between the high and low tide lines (13.1)
the region of a coast between the high and low tide lines. Also called the littoral zone (1.3)
the region of a coast between the high and low tide lines. Also called the intertidal zone (1.3)
another name for the beach face (13.1)
an offshore deposit of sand parallel to the shoreline (13.1)
the movement of water parallel to a shoreline produced by the approach of waves at an angle to the shore (13.2)
the upward motion of a wave on a beach (typically takes place at the same angle that the waves are approaching the shore) (13.1)
the wash of wave water down the slope of a beach (13.1)