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14.4.5. Littoral modeling

Littoral modeling

The geological action of the sea is what determines the coastal modeling  through different movements of its waters:

  • Sea currents. They are large masses of marine water that move in seas and oceans. Surface currents are caused by the action of the wind, and deep currents, by differences in density (temperaturesalinity, etc.) between two bodies of water.
  • TidesThey are ascents and descents of the sea level due to the gravitational pull of the Moon and, tolesser extent, the sun. Every day, any area of ​​the Earth aligns itself twice with the Moon, producing two rises (high tide) and two decreases (low tide) in sea level.

Some particular cases of tides are spring tides, when the Sun and the Moon are aligned with the Earth, which occur twice a month, at full moon and new moon. On the other hand, neap tides occur when the Sun, the Earth and the Moon are arranged forming an angle of 90º, which also occurs twice a month, in the first quarter and the last quarter.

  • Waves. Is heOscillatory movement of the particles on the surface of the sea that is produced by the action of the wind when brushing against the surface of the sea. The waves are the main component of the marine geological process, and it acts in several ways:
    • Hitting the wave directly against the shore.
    • Through the pressure exerted by the air that is between the cracks and fissures when compressed by the wave.
    • Abrasion produced by the onslaught of waves loaded with rocky fragments.

In stormy situations, the water has a lot of energy and causes erosion, carrying away materials. In anticyclonic situations, the energy of the water is lower, and sedimentation occurs.

The geological action of the sea produces forms of erosion and sedimentation.

Forms of marine erosion

The erosion of the coast is not uniform at all costs, as it depends on the force of the water, the type of expense and type of constituent materials.

If the rocks are heterogeneous, erosion will produce recesses , such as covesinlets or bays, and ledges, such as headlands in the strongest rocks.

The cliffs are the most characteristic coastal erosive forms. The waves hit the base of the cliffseroding and undermining the base. The erosive action of the waves makes them penetrate deeper and deeper into the rock face. The upper rocks leave an unstable cantilever that ends up giving way, and receding the cliff. Large rock fragments fall onto flat horizontal surfaces called abrasion pads, located at the foot of the cliff.

Depending on the composition and structure of the rocks and the presence of fractures, the receding of the cliff can leave residual forms such as islets and arches that will end up eroding.

Acantilado

Acantilado de los Gigantes, Santiago del Teide (Tenerife)


Forms of marine sedimentation

The clasts, due to the action of the waves and the friction with the gravel and sand, are eroding and rounding until they are reduced to sand that is dragged along the coast. In areas where the wave energy is lower, it is where sedimentation will occur  in the form of sandy beaches.

The coastal bars are long, linear sand deposits close to the coast. If they are attached to the continent they are called littoral arrows. If the arrow connects an island with the coast, it is called a tombolo (Peñíscola, for example), and if it grows until it isolates a bay from the open sea, it gives rise to lagoons (Valencia, for example).

The marshes (Guadalquivir, for example) are areas of the river mouths, flat, with herbaceous vegetation, in which, due to the action of the tides, fresh water is mixed with salt water.

Playas de Papagayo (Lanzarote)

Papagayo Beach (Lanzarote)

Answer in your notebook

14.11.- Why do we find tombstones in the beach areas and not in the cliff areas?