At the water table, you will have pores of rock that are saturated completely with water. The best case scenario is when there is no confining layer of rock above it that will pressurize the water enough to push it up too high after the water table has been reached. The confining layer is called the aquitard layer; it isn't very permeable so water doesn't get through easily. Aquiclude layers have no permeability to water at all. There is water beneath that under pressure. If you reach that layer, you will get artesian water or confining water. Beneath that is more rock and finally what's called the bedrock aquifer. Springs that pop up through faults under pressure are called artesian wells because this is the layer that water comes from. Artesian wells are areas of discharge of the groundwater to the earth's surface. Streams that pop up out of nowhere are also discharge areas. Playas in deserts are the same type of place. In a perfect system, we humans would extract water from wells in the underground aquifers in the exact amount it is being replaced through precipitation. Unfortunately, this is not happening in many parts of the world. Too much water is being pumped out of aquifers and the ground water drops. The earth itself can drop as a result; this leads to things like subsidence or sinking of ridges and sections of earth you might see in the American Southwest. These areas need the pore pressure of water in the rock's pores to hold up the earth. Without this pressure, the earth just sinks.
HYDROLOGY-BASED EARTH FEATURES When limestone and other salts dissolve in and around the earth, you get what is called karst. Karst can mean a lot of things. You can have karst towers above the ground where rock is left over as a tower after some of it has dissolved away. Caverns, disappearing streams, and sinkholes are all types of karst. Acid rain will accelerate the formation of karst because it makes carbonic acid. Carbonic acid is rough on the calcite in limestone and will dissolve other salts as well. What happens to dissolved calcite, which is in solution underground? It will often redeposit elsewhere. When it does, it is called tufa or travertine. Speleothems are travertine deposits in caves. You know them as stalactites and stalagmites. 220
