Global Distribution of Coastal Plains
Coastal plains are found across the world, bordering continents and large landmasses. North America features prominent examples, including the vast Atlantic Coastal Plain which stretches from Cape Cod, Massachusetts, down to Florida. This plain connects with the Gulf Coastal Plain, extending westward along the Gulf of Mexico and northward along the Mississippi River valley into Illinois.
In Europe, parts of the Great European Plain, particularly along the North Sea, exemplify coastal plain formations in countries like the Netherlands and Belgium. The Indian subcontinent also hosts extensive coastal plains on both its eastern and western flanks. India’s Eastern Coastal Plain lies between the Eastern Ghats and the Bay of Bengal, while the narrower Western Coastal Plain runs between the Western Ghats and the Arabian Sea, stretching from Gujarat to Kerala.
Australia contains notable coastal plains such as the South East Coastal Plain in Victoria and the Swan Coastal Plain in Western Australia, which encompasses the city of Perth. Coastal plains are also present in Africa and along western South America, where the Andes Mountains meet the Pacific Ocean. These low-lying areas often extend inland from the seashore.
Defining Features of Coastal Plains
Coastal plains are characterized by their low elevation and generally flat or gently sloping topography. The land surface often lies only a few meters above mean sea level and typically dips at an angle less than one degree.
The composition of these plains primarily consists of unconsolidated sediments like gravel, sand, silt, and clay. These sedimentary deposits often result in fertile soils. Hydrologically, coastal plains are typically wet, featuring numerous rivers, estuaries, and extensive wetlands and marshes due to their nature.
Their climate is often mild, ranging from humid subtropical to tropical, heavily influenced by the moderating effects of the adjacent ocean. While northern coastal plains might experience cold, snowy winters, those in southern regions tend to have milder winters and hot, humid summers, sometimes with hurricane activity. This combination of flat terrain, sedimentary soils, abundant water, and a maritime climate defines these distinctive geographical regions.
How Coastal Plains Form
Coastal plains primarily form through two main geological mechanisms: sedimentation and changes in sea level. Over long periods, rivers carry sediments from inland areas to the coast. These materials are then deposited along the shoreline and on the continental shelf, gradually accumulating and building up the landmass.
Sea level fluctuations also contribute substantially to the formation of coastal plains. Many originated as continental shelves, flat areas located below sea level. When global sea levels drop during ice ages, these submerged shelves become exposed, forming new coastal plains. Conversely, as glaciers melt and sea levels rise, previously exposed coastal plains can be inundated, and sediments are often reworked and moved inland.
The interplay between sediment supply and sea level changes dictates how a coastal plain evolves. High rates of sedimentation can cause the shoreline to advance seaward, even if sea levels are rising. Periods of falling sea levels also promote sediment deposition and the accretion of coastal land, sometimes leading to the formation of features like barrier islands. These dynamic processes, occurring over geological timescales, shape the characteristic flat and low-lying topography of coastal plains.
Ecological and Human Significance
Coastal plains are ecologically significant, supporting diverse ecosystems and acting as critical habitats for many species. They often contain extensive wetlands, marshes, and estuaries, which are productive environments where freshwater mixes with saltwater. These areas serve as crucial nurseries for various fish and shellfish, and provide feeding and breeding grounds for migratory birds and other wildlife. Coastal wetlands also filter pollutants and excess nutrients from water runoff, contributing to water quality.
From a human perspective, coastal plains have historically attracted dense settlements. Their flat terrain makes them suitable for construction and the development of infrastructure. The fertile, often sedimentary soils found in these regions are productive for agriculture.
Access to water resources, including rivers and oceans, facilitates trade and fishing, making these areas economic hubs. Many major cities globally, such as New Orleans, Houston, Cairo, and Beirut, are situated on or near coastal plains, highlighting their importance for human civilization and economic activity.