Endorheic basin

Some lakes sit in a closed bowl.

These lakes do not flow to the ocean. Instead, the water stays in one place. The sun dries the water away.

This leaves salt behind in the basin. These places are often in dry deserts.

They can also be high in the mountains. Some of these lakes are very large. The Caspian Sea is the largest one. It is a very special place for water.

Most water on Earth flows to the ocean. But some water stays in a closed area. This is called an endorheic basin. The word comes from French. It means "flow within."

In these basins, water cannot flow out to the sea. Instead, the water flows into lakes or swamps. The water only leaves through evaporation. This is when the sun turns water into vapor.

Because water leaves but minerals stay, these places change. Minerals from rocks wash into the water. When the water dries up, the minerals stay behind. This can make the water very salty. These are often called salt lakes.

These basins are often in dry deserts. They can also be high in the mountains. Many are found in the middle of landmasses. The Caspian Sea is the largest one. It is a huge inland body of water.

Sometimes, humans change how this water moves. We build dams or move water for farms. This can make these lakes shrink. When they shrink, they can become very salty or dirty.

Most water on Earth travels through rivers to reach the ocean. However, some water stays trapped in a special area called an endorheic basin.

The name comes from a French word meaning "flow within." These are also called closed basins or terminal basins. They are different from open regions where water eventually flows into the sea. Instead, these basins act as local limits for how water moves.

In these basins, the way water works is quite unique. Water flows into lakes, swamps, or seasonal pools. Because the land shapes, like mountains, block the way out, the water cannot reach the ocean. The only way for water to leave is through evaporation or seepage.

When the sun heats the water, it turns into vapor and rises. This process leaves behind minerals that were carried in by the water. Over time, these minerals build up and can make the water very salty.

Scientists and explorers have studied these basins for a long time. We know that many areas were different during the Ice Ages. For example, the Sahara might have had huge lakes long ago. Even the Black Sea was once an independent system. It only connected to the Mediterranean Sea after the terrain broke through.

Some basins, like the Malheur/Harney system in Oregon, were connected to rivers as recently as 1,000 years ago.

There are many famous examples of these closed systems around the world. The Caspian Sea is the largest inland body of water on Earth.

In Africa, the Chad Basin covers about 2.434 million square kilometers. Australia has the highest percentage of endorheic regions at 21 percent. North America has the least at only five percent. About 18 percent of all Earth's land drains into these types of basins. Much of this land is found in the interior of Asia.

These basins are important to understand because they are very sensitive. Since water cannot flow out, pollution can get trapped and build up.

Humans can also change these systems by building dams or aqueducts. This can cause lakes to shrink and become more salty. When lakes dry up, they can leave behind salt flats or playas. These flat surfaces are sometimes used for aviation runways or land speed records. They show us how much the landscape can change over time.

An endorheic basin is a unique drainage system that retains water within its boundaries. Most water on Earth moves through rivers to reach the ocean, but these basins do not allow such an outflow. Instead, they are also known as closed basins, terminal basins, or internal drainage systems. These regions contrast with exorheic regions, where surface waters eventually drain into the sea. In an endorheic system, the water stays within the landmass.

The mechanism of an endorheic basin relies on local topography to trap water. Natural geological formations, such as mountain ranges, often act as barriers that block water egress to the ocean. Water flows into the basin through rivers or precipitation, forming lakes, swamps, or seasonal pools. Because there is no river outlet, the water can only leave through two processes: evaporation or seepage.

As water evaporates into the atmosphere, it leaves behind dissolved substances. Minerals are leached from the surrounding rocks and carried into the basin by inflowing water. When the water evaporates, these minerals and erosion products are deposited on the basin floor. Over time, this constant input can make the water highly saline. This process often transforms these bodies of water into salt lakes.

Endorheic basins can be categorized by their stability and the permanence of their water. Some contain permanent lakes, while others host seasonal lakes that change size during different seasons. In extreme cases, a basin may be described as arheic if there is no discernible drainage system at all. Some basins are currently stable because climate change has reduced precipitation. If precipitation is too low, a lake may no longer form in the basin.

History shows that these systems are not always permanent. During the Ice Ages, many areas that are now dry deserts were actually large lakes. For example, the Sahara may have contained lakes larger than any existing today. The Black Sea was likely once an independent endorheic system. It only connected to the Mediterranean Sea after the terrain between them broke through.

These basins are globally significant and vary greatly by continent. Approximately 18 percent of Earth's land drains to endorheic lakes or seas. The largest of these land areas is found in the interior of Asia. Australia has the highest concentration of these regions at 21 percent. In contrast, North America has the lowest percentage at only five percent. The Caspian Sea is a notable example, as it is the world's largest inland body of water.

Endorheic regions are highly sensitive to environmental changes and human activity. Because pollution cannot flow out to the ocean, it becomes trapped and accumulates in the basin. This can lead to toxic surges of pollutants that harm ecosystems. Human engineering, such as building dams or aqueducts, can also divert water away from these basins. This can cause lakes to contract dramatically, increasing salinity and disrupting local life.

When these lakes dry up completely, they often leave behind salt pans, also called playas. These are large, flat, and hardened surfaces. Because they are so level, they are sometimes used for aviation runways or land speed record attempts. These landscapes serve as a reminder of how water and climate shape our world.