A spring may be the result of karst topography where surface water has infiltrated the Earth's surface (recharge area), becoming part of the area groundwater. The groundwater then travels through a network of cracks and fissure—openings ranging from intergranular spaces to large caves. The water eventually emerges from below the surface, in the form of a karst spring.
The forcing of the spring to the surface can be the result of a confined aquifer in which the recharge area of the spring water table rests at a higher elevation than that of the outlet. Spring water forced to the surface by elevated sources are artesian wells. This is possible even if the outlet is in the form of a 300-foot-deep (91 m) cave. In this case the cave is used like a hose by the higher elevated recharge area of groundwater to exit through the lower elevation opening.
Non-artesian springs may simply flow from a higher elevation through the earth to a lower elevation and exit in the form of a spring, using the ground like a drainage pipe.
Still other springs are the result of pressure from an underground source in the earth, in the form of volcanic activity. The result can be water at elevated temperature such as a hot spring.
Sunrise at Middle Spring, Fish Springs National Wildlife Refuge, Utah
The action of the groundwater continually dissolves permeable bedrock such as limestone and dolomite, creating vast cave systems.[1]
Types
Seepage or filtration spring. The term seep refers to springs with small flow rates in which the source water has filtered through permeable earth.
Fracture springs, discharge from faults, joints, or fissures in the earth, in which springs have followed a natural course of voids or weaknesses in the bedrock.
Tubular springs, in which the water flows from underground caverns
Flow
Spring discharge, or resurgence, is determined by the spring's recharge basin. Factors that affect the recharge include the size of the area in which groundwater is captured, the amount of precipitation, the size of capture points, and the size of the spring outlet. Water may leak into the underground system from many sources including permeable earth, sinkholes, and losing streams. In some cases entire creeks seemingly disappear as the water sinks into the ground via the stream bed. Grand Gulf State Park in Missouri is an example of an entire creek vanishing into the groundwater system. The water emerges 9 miles (14 km) away, forming some of the discharge of Mammoth Spring in Arkansas. Human activity may also affect a spring's discharge—withdrawal of groundwater reduces the water pressure in an aquifer, decreasing the volume of flow.[2]
Classification
Fontaine de Vaucluse or Spring of Vaucluse in France discharges about 470 million US gallons (1,800,000 m3) of water per day at a rate of 727 cubic feet (21 m3) per second.
Springs are often classified by the volume of the water they discharge. The largest springs are called "first-magnitude", defined as springs that discharge water at a rate of at least 2800 liters or 100 cubic feet (2.8 m3) of water per second. Some locations contain many first-magnitude springs, such as Florida where there are at least 27 known to be that size; the Missouri and Arkansas Ozarks, which contain 10[3][4] known of first-magnitude; and 11[5] more in the Thousand Springs area along the Snake River in Idaho. The scale for spring flow is as follows:
Magnitude Flow (ft³/s, gal/min, pint/min) Flow (L/s)
1st magnitude > 100 ft³/s 2800 L/s
2nd magnitude 10 to 100 ft³/s 280 to 2800 L/s
3rd magnitude 1 to 10 ft³/s 28 to 280 L/s
4th magnitude 100 US gal/min to 1 ft³/s (448 US gal/min) 6.3 to 28 L/s
5th magnitude 10 to 100 gal/min 0.63 to 6.3 L/s
6th magnitude 1 to 10 gal/min 63 to 630 mL/s
7th magnitude 2 pint to 1 gal/min 8 to 63 mL/s
8th magnitude Less than 1 pint/min 8 mL/s
0 magnitude no flow (sites of past/historic flow)
Water content
Main article: Mineral spring
Pruess Lake is spring-fed in the arid Snake Valley of Utah.
Minerals become dissolved in the water as it moves through the underground rocks. This may give the water flavor and even carbon dioxide bubbles, depending on the nature of the geology through which it passes. This is why spring water is often bottled and sold as mineral water, although the term is often the subject of deceptive advertising. Springs that contain significant amounts of minerals are sometimes called 'mineral springs'. (Springs without such mineral content, meanwhile, are sometimes distinguished as 'sweet springs'.) Springs that contain large amounts of dissolved sodium salts, mostly sodium carbonate, are called 'soda springs'. Many resorts have developed around mineral springs and are known as spa towns.
Water from springs is usually clear. However some springs may be colored by the minerals that are dissolved in the water. For instance, water heavy with iron or tannins will have an orange color.[1]
In parts of the United States a stream carrying the outflow of a spring to a nearby primary stream may be called a spring branch or run. Groundwater tends to maintain a relatively long-term average temperature of its aquifer; so flow from a spring may be cooler than a summer day, but remain unfrozen in the winter. The cool water of a spring and its branch may harbor species such as certain trout that are otherwise ill-suited to a warmer local climate.