(c) Stacks. A stack is an isolated remnant of rock left standing on a wave-cut bench as the result of
erosion by waves on all aide of a wave-cut cliff.
(2) Depositional Features Created by Wave Action. Where there is an abundant supply of
unconsolidated material along the coast, the predominant geologic process is deposition. As waves approach the
shore head-on, they sweep up loose sediments and carry them landward. The return flow of water washes much
of the sediment back toward the sea. In addition, waves that meet the shore at an angle may create longshore
currents, which transport material parallel to the shoreline. This complex reworking of coastal sediments is
responsible for the development of several different types of depositional features (see figure 2-13).
(a) Bars. Bar is a generic term applied to any of a number of forms of elongate embankments of
sand and gravel built on the sea floor by the action of waves and/or currents. These depositional features are
further described by their positions in relationship to other coastal features. For example, a baymouth bar is a bar
that extends partially or entirely across the mouth of a bay. A crescent bar is a crescentic sand or gravel ridge that
forms between two promontories, or headlands. These types of bars are formed by the flow of seawater into an
inlet or bay; consequently, the curved outline of a crescent bar is concave toward the ocean. A cuspate bar is a
pointed bar with a tip that projects seaward. These bars are formed where there are conflicting shore currents. A
special type of bar, known as an offshore bar or barrier island, is a sand and gravel ridge that lies offshore and is
isolated from the mainland. Barrier islands commonly contain dunes, vegetated zones, and swampy terraces on
the lagoonside of the island.
(b) Tombolos. Tombolos are ridges of sand or gravel that have been deposited in such a way that
they connect one island to another or an island to the mainland.
(c) Spits. Elongate ridges of sand and gravel that project from the land to the sea are called spits.
Most spits are simply extensions of bars, and they are built as longshore currents deposit sediment in areas where
the water suddenly deepens, such as at the mouth of a bay.
Figure 2-13. Depositional features of wave action