A plain is a broad area of relatively flat land. Plains are one of the major landforms, or types of land, on Earth. They cover more than one-third of the world’s land area. Plains exist on every continent.

Grasslands

Many plains, such as the Great Plains that stretch across much of central North America, are grasslands. A grassland is a region where grass is the main type of vegetation.

In North America, temperate grasslands—those in places with warm summers and cold winters—are often called prairies. In areas with little rain and snow, short grasses grow. In areas that receive more rain and snow, tall grasses can grow 1.5 meters (5 feet) high. However, most tallgrass prairies have been plowed under and are now farmland or pasture.

The Great Plains have supported a wide variety of cultures for thousands of years. The so-called “Plains Indians” are actually more than two dozen tribes. Communities include Blackfoot, native to the Canadian province of Alberta; Arapaho, whose center today is in the U.S. state of Wyoming; and Kickapoo, many of whom live today in the Mexican state of Coahuila.

In Asia and eastern Europe, temperate grasslands are called steppes. Steppes usually do not receive enough rain for tall grasses and trees to grow.

Tropical grasslands are called savannas. Savannas exist in places that are warm throughout the year. They often have scattered trees. Savannas such as the Serengeti plains stretch across much of central Africa. They are also found in Australia, South America, and southern North America.

Not all plains are grasslands. Some, such as Mexico’s Tabasco Plain, are forested. Forested plains have different types of trees, shrubs, and other vegetation.

Deserts can also be plains. Parts of the Sahara, a great desert in North Africa, are plains.

In the Arctic, where the ground is frozen, plains are called tundra. Despite the cold, many plants survive here, including shrubs and moss.

Plain Formation

Plains form in many different ways. Some plains form as ice and water erodes, or wears away, the dirt and rock on higher land. Water and ice carry the bits of dirt, rock, and other material, called sediment, down hillsides to be deposited elsewhere. As layer upon layer of this sediment is laid down, plains form.

Volcanic activity can also form plains. Lava plains form when lava pushes up from below ground and flows across the land. The earth in a lava plain is often much darker than the surrounding soil. The dark earth is a result of the lava, mostly a dark-colored mineral called basalt, broken down into tiny particles over millions of years.

The movement of rivers sometimes forms plains. Many rivers run through valleys. As rivers move from side to side, they gradually erode the valley, creating broad plains.

As a river floods, it overflows its bank. The flood carries mud, sand, and other sediment out over the land. After the water withdraws, the sediment remains. If a river floods repeatedly, over time this sediment will build up into a flood plain. Flood plains are often rich in nutrients and create fertile farmland. The flood plain surrounding Africa’s Nile River has helped Egyptian civilization thrive for thousands of years.

Alluvial plains form at the base of mountains. Water carrying sediment flows downhill until it hits flat land. There, it spreads out, depositing the sediment in the shape of a fan. The Huang He River in China has created an alluvial plain that covers about 409,500 square kilometers (158,000 square miles). Because much of the sediment the Huang He carries is yellowish in color, it is also called the Yellow River.

Many rivers deposit their sediment in the ocean. As the sediment builds up, it might eventually rise above sea level, forming a coastal plain. The Atlantic Coastal Plain stretches along much of the eastern coast of North America. These broad underwater plains slope gently down beneath the water.

Abyssal plains are found at the bottom of the ocean. These plains are 5,000 to 7,000 meters (16,400 to 23,000 feet) below sea level, so scientists have a hard time studying them. But scientists say abyssal plains are among the flattest, smoothest places on Earth.