12.S: Summary

Summary

Shoreline processes are complex, but important for understanding coastal processes. Waves, currents, and tides are the main agents that shape shorelines. Most coastal landforms can be attributed to moving sand via longshore drift, and long-term rising or falling sea levels.

Oceans absorb solar energy, which is distributed by currents throughout the world. Circular surface currents, called gyres, rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Thermohaline deep circulation connects the world’s deep ocean waters: when shallow poleward moving warm water evaporates, the colder, saltier, and denser water sinks and becomes deep-water currents. The connection between shallow and deep-ocean circulation is called the global conveyor belt.

Tides are the rising and lowering of sea level during the day and are caused by the gravitational effects of the Sun and Moon on the oceans. There are three types of tidal patterns: diurnal, semidiurnal, and mixed. Typical tidal ranges are approximately 1 m (3 ft). Extreme tidal ranges are around 18 m (60 ft).

The shoreline is the interface between water and land and is divided into five zones. Processes at the shoreline are called littoral processes. Waves approach the beach at an angle, which cause the waves to bend towards the beach. This bending action is called wave refraction and is responsible for creating the longshore current and longshore drift—the process that moves sand along the coasts. When the longshore current deposits sand along the coast into quieter waters, the sand can accumulate, creating a spit or barrier called a baymouth bar, which often blocks bays and harbors. Inconvenienced humans create methods to keep their harbors open and preserve sand on their beaches by creating jetties and groins, which negatively affect natural beach processes. Emergent coasts are created by sea levels falling, while submergent coasts are caused by sea levels rising.

Marine depositional environments include abyssal plains, submarine fans, the continental slope, the continental rise and the lower and upper shoreface.  Transitional depositional environments include beaches, deltas, tidal flats, lagoons and reefs.  Sediments range from fine clay and mud to sand to coarse gravel, depending on water depth and movement of water. Fossils and shoreline depositional environments can tell the geologic history of the region, including rise and fall of sea level.  Hydrocarbon deposits used by humans can be found in shoreline environments.