Dry lake

A dry lake is a large basin or depression in the landscape. It is a place that once held a standing body of water. Scientists call these landforms playas.

A dry lake forms when water from rain or other sources flows into a low area. This creates a pond or a lake. If the annual evaporation rate is higher than the annual water inflow, the lake disappears. This process leaves behind a flat bed of clay or minerals. These basins are common in semi-arid to arid regions of the world.

The formation of a dry lake involves a specific cycle of water and minerals. First, water collects in a depression. This water might come from rain or from intersecting with a water table. As the water sits, it begins to evaporate into the atmosphere. If the water leaves faster than it is replaced, the lake bed dries out. During this process, salts that were dissolved in the water precipitate, or settle out. These are called evaporite minerals. Over time, these minerals like sodium carbonate and borax build up to create a crust.

There are different types of dry lake beds based on their surface material. If the floor is covered by alkaline compounds, it is an alkali flat. If the floor is covered by salt, it is a salt flat. When the basin is primarily salt, it is also called a salt pan or a salt pan.

In the western United States, a dry terminus of an internally drained basin is called hardpan. The appearance of the surface also changes based on water levels. Thin layers of moving water create smooth surfaces. Thicker water layers can create a cracked-mud surface with teepee-like structures. If there is very little water, dunes may form.

Different cultures use various names for these unique landscapes. In Mexico and the western United States, the term playa is common. In South America, people use the terms salar or salina.

In South Africa, the word pan is used. Australian terms include salt pans and clay pans. In Arabic, they are called a sabkha or a shott. Central Asian regions use the term takyr, while in Iran, they are called kavir.

Dry lakes host surprising geological and biological phenomena. At Racetrack Playa in Death Valley, California, "sailing stones" move across the surface. This happens through a rare coincidence of events. First, the playa fills with water deep enough to form ice. At night, the water freezes into thin sheets of windowpane ice. When the sun comes out, the ice melts and cracks into floating panels. Light winds then blow these panels, propelling the rocks across the mud.

These stones move only once every two or three years.

These environments also support specialized life forms. Many playas are ringed by salt-tolerant plants like saltbrush. These plants provide food for herbivores. Some species are found nowhere else, such as the plant Lepidium davisii. In 2006, a giant fairy shrimp was discovered in Idaho. This shrimp can survive for years as tiny, undetectable cysts in the dry mud.

However, these ecosystems face threats. Pollution from cattle feedlots and runoff from farms can cause erosion. Even non-native shrubs like Kochia prostrata can drain the water and crowd out native plants.

Humans find many uses for these flat, hard surfaces. The smoothness makes them perfect for high-speed vehicles. The Bonneville Salt Flats in Utah and Black Rock Desert in Nevada are used for land speed records.

Some dry lakes also serve as air bases, such as Edwards Air Force Base in California. Additionally, humans extract valuable minerals from the subsurface brines. For example, lithium is a major resource found in the Salar de Uyuni.

Recent studies show that over half of the world's large lakes are drying up due to rising temperatures and human use.