A pluvial lake is a landlocked basin (endorheic basin) which fills with rainwater during times of glaciation, when precipitation is higher. Pluvial lakes that have since evaporated and dried out may also be referred to as paleolakes.
The word pluvial comes from the Latin pluvia, which means "rain".
They represent changes in the hydrological cycle — wet cycles generate large lakes, whereas dry cycles cause the lakes to dry up leaving large flat plains. Accumulated sediments show the variation in water level. During glacial periods, times when the lake level is fairly high, mud sediments will settle out and be deposited. At times in between glaciers (interglacial), salt deposits may be present due to the arid climate and evaporation of lake water.
Several pluvial lakes formed in the southwestern United States during the glaciation of the late Pleistocene epoch. One of these was Lake Bonneville in western Utah which covered roughly 19,000 square miles (49,000 km2). When Lake Bonneville was at its maximum water level, it was 1,000 feet (300 m) higher than the Great Salt Lake.
Fresh water mollusks have been found in mud deposits from the Searles Lake in California and suggest that the water temperature was about 7 degrees Fahrenheit (or 4 degrees Celsius) cooler than current temperatures. Radiocarbon dating of the youngest mud beds yield dates from 24,000 to 12,000 years ago.
When warm air from arid regions meets chilled air from glaciers, it creates cloudy, cool, rainy weather beyond the terminus of the glacier. This type of humid climate was present during the last glacial period in North America, and causes more precipitation than evaporation. The increase in rainfall fills the drainage basin and forms a lake.
During interglacial periods, the climate becomes arid once more and causes these lakes to evaporate and dry up.
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