The Earth’s surface is a mosaic of colossal landforms. While mountains and plateaus often draw attention for their dramatic elevation, a significant portion of the continents consists of plains. These are vast stretches of land characterized by low relief and gentle slopes. Formed over geological timescales, these immense, flat expanses cover more than one-third of the world’s land area. The largest of these plains represents one of the planet’s most extensive terrestrial features, providing insight into the world’s largest river system and most biodiverse tropical region.
Identifying the World’s Largest Plain
The world’s largest plain is the Amazon Plain, synonymous with the Amazon Basin in South America. This feature covers approximately 7 million square kilometers (2.7 million square miles), making it the most extensive lowland region globally. The Amazon Plain is nearly as large as the contiguous United States, stretching across a significant portion of the continent and encompassing territory within nine different nations.
The territory is shared primarily by Brazil, which holds the largest portion, along with parts of Peru, Bolivia, Colombia, Ecuador, Venezuela, Guyana, Suriname, and French Guiana. Its size dwarfs other major lowlands, such as the West Siberian Plain. The Amazon Plain’s scale results directly from its formation and the volume of water and sediment transported by its primary river system.
Defining the Characteristics of a Plain
A plain is defined as a broad expanse of relatively flat land that does not experience substantial changes in elevation. These landforms are typically low-lying, though some can exist at higher elevations. The defining trait is minimal local relief, meaning the difference between the highest and lowest points within a small area is slight. Plains often occur as lowlands along valleys, at the base of mountain ranges, or as coastal plains bordering the sea.
The formation of plains results from depositional processes, where sediments are carried and laid down over long periods by water, ice, or wind. For river-formed plains, such as the Amazon, this involves the continuous deposition of alluvial material eroded from distant highlands. These layers accumulate over millions of years, creating a deep, flat, and often fertile surface. Structural plains are another type, formed by horizontal rock strata undisturbed by tectonic activity.
Geographic Scope and Specific Physical Features
The Amazon Plain is bordered by the Andes Mountains to the west, the Guiana Shield to the north, and the Brazilian Highlands to the south. This geographical enclosure creates a bowl-shaped depression that collects water from a vast drainage area. A primary physical feature is the plain’s extremely low gradient; the Amazon River’s slope averages only a few centimeters per kilometer for much of its course. This minimal incline results in slow-moving water and extensive floodplains.
The hydrological system includes the Amazon River and its thousands of tributaries, which collectively discharge roughly 20% of all fresh water carried to the oceans. The plain is divided into two primary terrain types based on flooding: the várzea (floodplain), which is seasonally inundated, and the terra firme (higher, non-flooding land). The climate is predominantly tropical, marked by consistently high temperatures and immense annual rainfall, supporting the dense vegetation that covers most of the region.
Ecological and Human Significance
The physical structure of the Amazon Plain supports the world’s largest tropical rainforest, Amazonia. This forest is a reservoir of biodiversity, housing an estimated 10% of all known species on Earth, including tens of thousands of plant species. The ecosystem plays a role in global climate regulation by serving as a carbon sink, storing large amounts of carbon in its biomass and soils. The forest also functions as an atmospheric water recycling system, generating much of its own rainfall through evapotranspiration.
Despite its size, the Amazon Plain is relatively sparsely populated. Most of the approximately 30 million inhabitants are concentrated in major cities along the river banks, such as Manaus and Belém. Human activity includes subsistence agriculture, resource extraction, and commercial endeavors like ranching and soybean farming. The fertile alluvial soils of the floodplains have historically supported indigenous communities who practice specialized agriculture adapted to the seasonal flood pulses.