The zone of aeration is a region in the ground in which pore spaces are fill with air.

The zone of saturation is the region in the ground in which pore spaces are filled with water.

Porosity is the percentage of the total volume of rock or sediment that consists of pore spaces. While permeability is the measure of a material's ability to transmit fluids.

Heavy rains and rapid melting of snow can trigger mass movement by saturating surface materials with water.

A spring forms whenever the water table intersects the ground surface.

A hot spring is 6 degrees Celsius to 9 degrees Celsius warmer than the mean annual air temperature where the spring occurs. There are more than 1000 hot springs in the U.S. The source of heat for most of these hot springs is cooling igneous rock.