Water Beneath the Surface Chapter 6.3 Water Beneath the Surface

The ground is made of many pore spaces and narrow joints and fractures in bedrock to create spaces for water to collect. Underground water supplies water for cities, livestock, and industry. More than 50% of this water in the US is for drinking.

Distribution and Movement of Water Underground After a rainfall some of the water runs off, some evaporates, and the rest soaks into the ground. The amount that ends up underground is dependent on the steepness of slopes, the nature of the surface materials, and the intensity of rainfall, and the type and amount of vegetation.

Distribution Some of the water that is soaked up does not travel far it becomes a surface film on soil particles. This is called the belt of moisture. This area helps rainwater seep into soil. More water will seep downward to the zone of saturation – this is where water fills all of the open spaces in sediment and rock. This is where groundwater is found. The upper part of the zone of saturation is the water table. Only below the water table is where water can be pumped.

Movement The amount of groundwater that can be stored is based on its porosity – that is the percentage of the total volume of rock or sediment that consists of pore spaces. Also permeability – the ability to release a fluid is important. Groundwater moves by twisting and turning through interconnected small openings. The groundwater moves more slowly when the pore spaces are smaller. Clay has high porosity but is impermeable to water. Aquifers are areas that move groundwater easily. This is a good source of well water.

Springs A spring forms whenever the water table intersects the ground surface. A spring is a flow of groundwater that emerges (comes up through the surface) naturally. This usually will form where the material doesn’t allow the permeability of water.

Hot Springs A hot springs is 6˚C to 9˚C warmer than the average annual air temperature. When groundwater is at very deep depths it heats up. If it rises to the surface it can emerge as a hot spring.

Geysers A geyser is an intermittent hot spring or a fountain where a column of water shoot up with great force as various times. Water will shoot up 30 to 60 meters. The most famous geyser is Old Faithful in Yellowstone National Park, it erupts 1 time per hour. These areas have very hot igneous rock. Cool groundwater enters this area and creates pressure as it is heating up the water. When the pressure is great enough it forces the water out, eventually releasing pressure.

Wells A well is a hole made into the zone of saturation. More than 65% of groundwater in the US is used for irrigation. The level of a well will rise during a period of rain and fall during dry seasons or when a lot of water is taken from the well. Most well must have a pump to pump out water. An artesian well is when groundwater will rise on its own. For this to happen the aquifer has to be tilted and there must be impermeable surfaces around the well so no water can leak out.

Treating Groundwater as a Nonrenewable Resource Groundwater is NOT endless. Groundwater can be used up faster than it is replaced. In areas where water is pumped faster than replaced it can cause the ground to sink. This causes of subsidence (a sinking ground).

Groundwater Contamination Common sources of groundwater pollution are sewage from septic tanks, farm wastes, and inadequate or broken sewers. If sewage contaminates groundwater bacteria can enter the water. Sometimes this water can be purified naturally, but not always. Fertilizers can also contaminate the groundwater. Most of the time if a well is contaminated it must not be used anymore.

Caverns Water containing carbonic acid dissolves limestone. When this happens we have water carrying calcium bicarbonate. A cavern is a naturally underground chamber. Erosion forms most caverns at or below the water table in the zone of saturation.

Caverns Some of the best part of caverns are depositional stone formations. This forms dripping water that produces limestone called travertine. These are called dripstone features.

Dripstone Features Stalactites are dripstone features. They are icicle-like stones that hang from the ceiling of a cavern. As water drips it leaves calcite behind and that forms a hollow tube called a soda straw. A stalactite can be plugged with water and this will cause more dripping to occur. Stalagmites form on the floor of a cavern These will form below the stalactites.

Karst Topography Karst topography is an area that has been formed because of the dissolving power of groundwater. In the US there are areas like this in Kentucky, Tennessee, Alabama, Indiana, and Florida. These areas have irregular terrain, with sinkholes. Sinkholes are areas where groundwater has removed rock so it creates depressions.

Sinkholes These form in one of 2 ways: Downward seeping rainwater dissolves limestone below the soil and creates shallow depressions that have gentle slopes. Sometimes sinkholes will occur suddenly from the roof of a cavern caving in. These are usually deep. Karst Topography also has a lack of drainage. The water will go into sinkholes. They are not going to have a lot of streams, or very short streams.