Water Beneath the Surface
Groundwater is water that exists in the pore spaces of soil and rock in the zone of saturation. It is a critically important source of freshwater.
Water Table: The upper level of the zone of saturation.
Aquifer: A permeable rock layer or sediment that can transmit groundwater freely. Good aquifers include sandstone and gravel.
Aquitard: An impermeable layer that hinders or prevents water movement, such as clay or shale.
Wells and Cones of Depression
When water is pumped from a well, the water table around the well is lowered. This creates a cone-shaped depression in the water table called a cone of depression.
If heavy pumping continues, the cone of depression can lower the water table over a large area and cause nearby shallow wells to go dry.
Karst Topography
Karst is a type of landscape formed from the dissolution of soluble rocks, most commonly limestone (calcium carbonate).
Formation: Rainwater becomes slightly acidic by absorbing carbon dioxide from the atmosphere, forming carbonic acid. This weak acid is very effective at slowly dissolving limestone, especially along fractures and bedding planes in the rock.
Over thousands of years, this dissolution carves out a network of underground drainage systems.
Karst Features
Caves (or Caverns): Large underground chambers formed by the dissolution of limestone by groundwater.
Sinkholes (or Dolines): Surface depressions formed when the roof of a cave collapses or when surface material is carried down into voids in the rock.
Stalactites and Stalagmites: Water seeping through the roof of a cave contains dissolved calcium carbonate. As the water drips, it leaves behind tiny deposits of calcite.
Stalactites grow down from the ceiling.
Stalagmites grow up from the ground.
When they meet, they form a column.
Disappearing Streams: Streams that flow into a sinkhole and continue flowing through the underground cavern system.