Every lake occupies a basin, and the story of how that basin formed can involve some of Earth's most powerful forces.
Lakes form wherever water collects in a depression or basin faster than it can completely drain away. Those basins can be carved by glaciers, created by movements in Earth's crust, left behind by volcanoes and rivers, or produced by several other geological processes.
Moving glaciers can carve enormous basins and leave depressions that later fill with water.
Learn MoreMovements of Earth's crust can create deep valleys and basins where water collects.
Learn MoreVolcanic craters and collapsed calderas sometimes become spectacular natural lake basins.
Learn MoreA looping river can change course and leave part of its old channel behind as a lake.
Learn MoreWater can slowly dissolve certain rocks and create depressions that eventually hold lakes.
Learn MoreFalling rock and soil can block a valley or river and create a natural dam.
Learn MoreGlaciers are enormous moving masses of ice capable of reshaping entire landscapes. As they move, they scrape and deepen valleys, and when the ice eventually melts, water can remain in the carved depressions. Glaciers also leave piles of rock and sediment called moraines, which may act like natural dams. Many lakes in northern North America and Europe were created or reshaped during past ice ages, and Lake McDonald in Glacier National Park is one example of a lake occupying a valley carved by glaciers.
Earth's outer crust is divided into moving tectonic plates, and their movements can stretch, crack, uplift, or lower sections of land. When part of the crust sinks between faults, a long and sometimes extremely deep basin may form. Water from rivers, rainfall, and groundwater can then collect inside it. Some of the world's deepest and oldest lakes occupy tectonic basins that have continued changing over millions of years.
Volcanoes can create natural bowls that later become lakes. A crater near the summit may fill with rain or snowmelt, while an enormous depression called a caldera can form when the ground collapses after a large eruption empties part of the magma chamber below. Crater Lake in Oregon is a famous example of a caldera containing a deep lake. Volcanic rocks can also block valleys and change drainage patterns, creating additional lakes around volcanic landscapes.
Rivers flowing across flat land often develop large bends called meanders. Erosion can gradually narrow the strip of land separating two parts of a bend until the river breaks through and begins following a shorter route. Sediment may then seal off the abandoned loop from the main channel. The isolated curved body of water is called an oxbow lake, although it may slowly fill with sediment and vegetation over time.
Some rocks, especially limestone, can slowly dissolve when exposed to slightly acidic groundwater. Over long periods, underground cavities may enlarge until the ground above sinks or collapses, producing a depression called a sinkhole. If the bottom can hold water and enough water enters, a sinkhole lake may develop. Landscapes containing many caves, springs, and sinkholes are known as karst landscapes.
Large landslides can suddenly move millions of tons of rock, soil, and debris into a river valley. If the debris completely blocks flowing water, it acts as a natural dam and a lake begins forming upstream. Some landslide dams survive for centuries, while others erode or collapse quickly and can release dangerous floods. Because of this uncertainty, newly formed landslide lakes are often closely studied by geologists and emergency officials.