Natural springs are captivating features where water emerges from below the Earth’s surface. These natural outlets result from specific geological and hydrological conditions that allow groundwater to flow to the surface.
The Source: Groundwater Basics
The journey of spring water begins with the water cycle, specifically precipitation. Rain and snow fall onto the Earth’s surface, and a portion of this water seeps into the ground through infiltration. This water eventually fills the tiny spaces, or pores, within rocks and soil, becoming groundwater. The uppermost level where these pores are saturated defines the water table.
Below the water table lies the saturated zone, where all available spaces are filled with water. Above it is the unsaturated zone, where pore spaces contain both air and water. Groundwater is the primary source for virtually all springs, accumulating underground and moving through the subsurface due to gravity.
Underground Pathways and Storage
Groundwater is stored and moves through specific geological formations called aquifers. Aquifers consist of permeable materials, such as sandstone, gravel, or fractured rock, which have interconnected pore spaces that allow water to flow freely. These formations act like natural underground reservoirs, holding significant quantities of water.
Conversely, confining layers are composed of impermeable materials like clay, shale, or basalt. These layers restrict water flow, acting as barriers that can trap groundwater. The interaction between permeable aquifers and impermeable confining layers influences how water is stored and moves underground.
How Water Rises to the Surface
The emergence of water at a spring occurs through several mechanisms, often driven by pressure and geological structure. One common way is when the water table intersects the land surface, such as on a hillside or in a valley. This allows groundwater to simply flow out due to gravity, forming what is known as a gravity spring or seepage spring.
In other cases, groundwater is under hydrostatic pressure, which is the pressure exerted by the weight of the water itself. This pressure can build up in confined aquifers, where an impermeable layer overlies the aquifer. If an opening penetrates this confining layer, the pressurized water can be forced upward and emerge as an artesian spring. The water in an artesian well can rise above the top of the aquifer due to this pressure, sometimes even flowing freely above the ground surface.
Characteristics of Springs
The characteristics of a spring, such as its flow rate and temperature, are direct reflections of its underground journey and the geological environment. The flow rate, or discharge, of a spring is influenced by factors like the size of the aquifer, the amount of water recharging the system, and the dimensions of the spring’s outlet. Significant rainfall or snowmelt often increases the recharge, leading to higher flow rates.
Spring water temperature is primarily determined by the depth and duration of its underground path, as well as the temperature of the surrounding rock. Water that travels deeper or through geothermally active areas can emerge as warm or hot springs. Conversely, shallow springs are more influenced by surface temperatures, but generally, spring water maintains a relatively constant temperature year-round due to the insulating effect of the ground.