BAHIA: GEOGRAPHY, PARTS AND EXAMPLES - GEOGRAPHY - 2025

The bay is a geographical feature on the coastline that consists of a notch or deep entrance forming a semicircle. This coastal conformation has a mouth or inlet of length equal to or less than the diameter of the semicircle it forms.

A bay is similar to a gulf and a cove, however there are some differences between these coastal landforms. The gulf is larger and with deeper waters while the cove has a narrow entrance.

Cata Bay (Venezuela). Source: Argus caracas / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Due to its geographical conformation in both coastal relief and depth, the bay partially dissipates the force of the waves and currents. Due to this, they are suitable areas for ports and for the use of their beaches for recreation and tourism.

Geography of the bays

The waves, currents and marine erosion

The coastline is the area of ​​interaction between land and sea, receiving the blow of waves and ocean currents. The waves represent a constant discharge of mechanical energy on the geological material that makes up the coast.

Depending on the type of material and how its layers are arranged in the coastal area, the waves will cause more or less erosion. Similarly, coastal currents generate a sediment drag force that contributes to the shaping of the coast.

Seawater erodes both by abrasive and wear action and by the solvent action of the acids contained in it.

Coastal geology

There are two basic conformations of the coastline, called concordant coasts and discordant coasts. On the concordant coasts, the layers of geological materials are arranged in layers parallel to the coast, alternating hard materials (granite, limestone) and soft material (sand, clay).

On the other hand, in the discordant coasts, the materials of different consistencies are arranged in strips perpendicular to the coast. Thus there is a strip of soft material that reaches the coast and parallel to it, there is an intrusion of hard material.

Formation of a bay on the concordant coast

On a concordant coast, the resistance to erosion is higher, since the layer of hard material runs parallel to the coast. In this way, it offers greater resistance to waves and protects the layer of soft material from it.

However, at the weakest points a gap opens in the wall of hard material. Then the sea penetrates through there and erodes the inner layer of soft material creating a crescent shape.

The entrance is generally relatively narrow due to the difficulty in eroding the shoreline material. However, over time parts of the hard front layer can collapse and form a larger entrance bay.

The distance that the sea can reach inland in this type of bay depends on the existence of a layer of hard material towards the interior of the coast. In addition, the altitude of the land above sea level has an influence, which defines how the water will act in this area.

Formation of a bay on jarring shore

In the case of jarring shores, the swell directly undermines the section of shoreline made up of soft material. If the entire coastline is made up of soft material, an extensive more or less straight beach will form.

Here the waves erode the coast, penetrating inland into a relatively shallow area. In this way a bay is created, only the mouth is wider compared to those created on concordant shores.

Other processes that influence the formation of bays

The movements of the earth's crust also contribute to the creation of bays, both by subsidence of coastal land or by horizontal displacements. For example, the separation of the present Baja California peninsula from the North American plate formed the Gulf of California and the Bay of Banderas.

Likewise, changes in sea level play an important role in the formation of some bays. Thus, the bays of the north South American coast were formed by the flooding of coastal valleys due to the rise in sea level.

Parts of the bay

Parts of a bay. Source: Feydey / Public domain

The bays vary in shape according to the geology of the terrain, the erosive and tectonic processes involved and the time elapsed. Among its basic parts are:

Headlands, entrance and body of water

The promontories, capes or points, are the extensions towards the sea of ​​hard material that form the lateral limits of the bay. A classic bay has two headlands, one on each side, but it may be that there is only one.

The space between the headlands or between a headland and the coastline, define the entrance to the bay. For its part, the body of water that makes up the bay corresponds to the intrusion of the sea in the undermined area.

Sea bottom

It is covered with sediments produced by erosion and those contributed by the waves. In some cases there are rivers that flow into the area and provide sediment.

The bottom relief is a slope that runs from the coastline to the open sea as part of the continental shelf. In tropical and subtropical areas it can be altered by the development of coral reefs.

Beach

It is the relatively flat area of ​​the boundary between the sea and the coast, marked by the low tide that accumulates the heaviest erosion products and generally made up of sand. In some cases the beach is not formed, the internal limit of the bay being marshes or rocky areas.

Examples of beans

San Francisco Bay (USA)

It is located on the Pacific coast of the USA in the state of California. This is an example of a coastal landform of some complexity, since it involves two bays, several estuaries, marshes and integrated swamps.

On the other hand, the area has suffered intensely from human intervention, filling in areas and excavating others. Some wetlands have been filled in and reclaimed throughout their history.

This complex of two bays, San Francisco in the center and San Pablo to the north, has a very narrow exit to the sea. This is the so-called Golden Gate or Golden Gate and is just 2.7 km long, extending there the bridge of the same name.

The limits of this complex of bays are the San Francisco peninsula and the Marín peninsula. In addition, there are four large islands, with Alcatraz in the center where the famous penitentiary converted into a museum is located.

Bay of Banderas (Mexico)

Bay of Banderas (Mexico). Source: User: (WT-shared) 2old at wts wikivoyage / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

It is located on the Pacific coast of Mexico between the states of Jalisco and Nayarit, being a typical bay, with a mouth of the same diameter as the semicircle that constitutes it. The entrance is bounded by Cape Corrientes to the south and Punta Mita to the north, with 100 km between them.

This bay has a depth of 900 m, making it one of the deepest in the world. The tourist area of ​​Puerto Vallarta is located here and it is also a breeding site for the humpback whale (Megaptera novaeangliae) from December to March.

Bay of Cádiz (Spain)

Bay of Cádiz (Spain). Source: European Space Agency / CC BY-SA (https://creativecommons.org/licenses/by-sa/2.0)

About 6,000 years ago the sea penetrated deep into the Atlantic coast of Andalusia where the estuary of the Guadalquivir River is now. There was a wide gulf called Tartessian and a little further south the sea penetrated to a lesser extent in the current area of ​​Cádiz.

This bay had been formed about 20,000 years ago due to the collapse of an ancient delta. Both areas were filled with sediments forming marshes, to the north the Tartessian Gulf disappeared and to the south the current Bay of Cádiz was formed.

On the other hand, the current island-peninsula of Cádiz was part of an archipelago, whose islands were connected by sedimentation and decrease in sea level. In this way the current Bay of Cádiz was created, which is a bay with an internal cove.

The entrance to the bay is bounded by the Rota promontory to the north and the former archipelago of Cádiz and León to the south, now a peninsula. The old island of Cádiz is linked to the island of León (San Fernando town) by an arm of sand (tombolo).

In turn, the old island of León is separated from the Iberian Peninsula only by the Sancti Petri channel, which is shallow and narrow. The bay of Cádiz is home to several ports, the most important of which is the port of Cádiz.

Cata Bay (Venezuela)

It is located in the Venezuelan Caribbean, on the central coast in the state of Aragua and is an example of the most characteristic shape of the bay, with a wide entrance but narrower than the diameter of its almost perfect semicircle.

It is limited by two promontories, with two beaches of fine sand in the background, separated by a section of the piedmont that has not yet eroded. In this case, it is an old valley flooded by rising sea level in the interglacial era on which the erosive action of the waves acted.

References

1. Araya-Vergara, J. (1986). Toward a classification of beach profiles. Journal of Coastal Research.
2. Ibarra-Marinas, D. and Belmonte-Serrato, F. (2017). Understanding the coastline: Dynamics and processes. Editum. University of Murcia.
3. Ortiz-Pérez, MA, and De la Lanza-Espino G. 2006. Differentiation of the coastal space of Mexico: A regional inventory. University texts series, Institute of Geography, UNAM.
4. Silva, R., Martínez, ML, Moreno, P. and Monroy-Ibarra, R. (2018). General aspects of the coastal zone. INECOL-IINGEN.
5. Villagrán-Colina, CP (2007). Coastal dynamics in the bay system between Ensenada Los Choros and Tongoy Bay, Coquimbo Region. Memory to qualify for the title of geographer. University of Chile.