What is a spring?
A spring is a water resource formed when the side of a hill, a valley bottom or other excavation intersects a flowing body of groundwater at or below the local water table, below which the subsurface material is saturated with water.
A spring is the result of an aquifer being filled to the point that the water overflows onto the land surface. They range in size from intermittent seeps, which flow only after much rain, to huge pools flowing hundreds of millions of gallons daily.
How are spring formed?
A spring is formed when the ground water, which is under pressure, flows out through a natural opening in the ground.
Most of the water that emerges at springs is meteoric in nature: that is, it originally fell as rain or snow on the surface of the Earth. At hot springs near active volcanoes, some of the water may have originated from magma, molten rock that also contains dissolved substances such as water. As magma cools and crystallizes in the Earth’s crust, it releases much of this water. Spring water also can be ancient sea water, although it usually is diluted with meteoric water.
Conceptually, the groundwater system associated with springs is simple. It consists of:
- A recharge area where water enters the subsurface;
- An aquifer or set of aquifers through which the water flows; and
- A discharge point where water emerges as a spring.
The existence of a spring requires that below the surface (the area commonly called the subsurface), the infiltrating water encounters a low permeability zone and is unable to continue to move downward as fast as it is supplied at the surface; as a result, the water spreads laterally until it intersects the land surface where erosion has lowered the topography to the water’s level (e.g., on the side of a canyon). *
A range of geological structures and topographic features can direct water to the surface and form a spring. Many seeps and small springs are associated with topographic depressions where the water table intersects the Earth’s surface. Larger springs usually are formed where geological structures, such as a faults and fractures, or layers of low-permeability material, force large amounts of water to the surface.
Characteristics of spring water.
Springs may be considered curious features because water appears to flow directly out of rocks. Yet springs are less mysterious when one understands where the water came from and how long it has been in the subsurface.
Water flow from spring.
The amount of water that flows from springs depends on many factors, including the size of the caverns within the rocks, the water pressure in the aquifer, the size of the spring basin, and the amount of rainfall. Human activities also can influence the volume of water that discharges from a spring—ground-water withdrawals in an area can reduce the pressure in an aquifer, causing water levels in the aquifer system to drop and ultimately decreasing the flow from the spring.