In Missouri a whole creek vanishes underground and reappears 9 miles away
At Grand Gulf State Park in Missouri, an entire creek sinks into its own bed and disappears. The water travels underground and resurfaces about 9 miles off, helping feed Mammoth Spring in Arkansas. Springs are where hidden groundwater finally breaks back into daylight, sometimes in astonishing volumes.
A spring forms wherever groundwater escapes an aquifer onto the surface, typically where the water table rises above ground level or the land drops away sharply. Gravity and hydrostatic pressure push it out. Flow ranges from almost nothing to more than 14,000 litres per second at the largest springs. Those discharging at least 2,800 litres a second are called first-magnitude, and Florida has at least 27 of them, with 10 more in the Ozarks of Missouri and Arkansas and 11 along Idaho's Snake River.
Geology shapes each type. In karst country, water dissolves limestone and dolomite into cave networks and emerges as karst springs. Contact springs appear on hillsides where an impermeable layer blocks downward seepage; fracture springs follow cracks in rock; tubular springs flow from caverns or old lava tubes. In an artesian spring, the recharge area sits higher than the outlet, so pressure shoves water straight up, even out of a cave 300 feet deep. Geothermal heat produces hot springs and geysers, and springs have even been found on the ocean floor, releasing warmer, less salty water.
Minerals picked up underground can flavour the water or make it fizz, which is why so much is bottled; by definition, mineral water carries at least 250 parts per million of dissolved solids. Iron or tannins can tint it orange, and some springs exceed the World Health Organization's arsenic limit of 10 parts per billion, a reminder that spring water is not automatically safe to drink without testing. Pumping groundwater nearby lowers aquifer pressure and weakens a spring's flow.
Because groundwater holds a fairly steady temperature, spring-fed streams run cool in summer and stay unfrozen in winter, sheltering trout that could not otherwise survive the local climate. People have long harnessed springs for mills, navigation and irrigation; Indigenous peoples of the American Southwest built spring-fed canals called acequias, a technique Spanish missionaries later adopted.
Source: Spring (hydrology)
