Geology Reference
In-Depth Information
Budgeting to build sandbars
All the materials that are removed from one area of a coast must end up somewhere
else. Waves and currents transport the sediments and then deposit them, creating
shoreline depositional features. Depositional features of a shoreline depend largely on
the amount of sediments available to be transported and deposited, or the
sediment
budget.
Figure 15-7:
Coastal features of
erosion.
If a shoreline has a balanced sediment budget, the amount of sediment being
eroded and carried away is being resupplied by sediment input so that the
amount of sediment in the coastal environment remains nearly constant. Sources
of sediment input include coastal erosion of headlands, as well as river deltas that
may bring sediments from the interior of the continent.
Beaches are the most common feature of coastal deposition. A
beach
is the relatively
narrow piece of land where the movement of currents, tides, and waves moves sediment
particles. Some beaches are full of white sand, but a beach can have larger rocks, or
rocks and sand of different colors, depending on what the source of the sediment is. For
example, in the Hawaiian Islands, most of the rocks being eroded by waves are basalt
formed from the eruption of Hawaiian volcanoes (see Chapter 7). This process results in
dark (sometimes even black) sand beaches.
