Aquifer -permeable layer transporting groundwater. Groundwater moves under the influence of gravity. If the water table intersects the surface a spring is formed. Under the proper circumstances an artesian well may form. A well whose top is above the artesian-pressure surface will flow freely.
Geysers are an interesting phenomenon.
Karst Topography and Cavern Formation Caves and caverns can form in areas underlain by limestone. The Forward Direction is to the right as you view this page. The Reverse Direction is to the left. Both equations have their own equilibrium constant. Imagine that this system is at equilibrium.