Presentation on theme: "S6E3.a Explain that a large portion of the Earth’s surface is water, consisting of oceans, rivers, lakes, underground water, and ice."— Presentation transcript:
S6E3.a Explain that a large portion of the Earth’s surface is water, consisting of oceans, rivers, lakes, underground water, and ice.
What you will learn in the section… Identify and describe the location of the water table. Describe an aquifer. Explain the difference between a spring and a well. Explain how caves and sinkholes form as a result of erosion and deposition.
A family lives 50 km from the nearest stream or lake and gets water from a well. Where does the water in the well come from? It comes from water stored underground.
Groundwater is water located within the rocks below the Earth’s surface. FYI (do not write) Millions of people get their water from groundwater. Groundwater not only is an important resource but also plays an important role in erosion and deposition.
Location of Groundwater Water is found underground in an area between two zones. Rainwater passes through the upper zone, called the zone of aeration. Farther down, the water collects in an area called the zone of saturation. In this zone, the spaces between the rock particles are filled with water. The two zones meet at a boundary known as the water table. Rises during wet seasons and falls during dry seasons
Aquifers The rock layer that stores groundwater and allows the flow of groundwater is called an aquifer. The more open spaces, or pores, between particles in an aquifer, the more water the aquifer can hold. The percentage of open space between individual rock particles in a rock layer is called porosity.
If the pores of a rock layer are connected, groundwater can flow through the rock layer. A rock’s ability to let water pass through is called permeability. A rock that stops the flow of water is impermeable.
The best aquifers usually form in permeable materials, such as sandstone, limestone, or layers of sand and gravel. Some aquifers cover very large areas. They are important source of water for cities and agriculture. The ground surface where water enters an aquifer is called the recharge zone. The size of the recharge zone depends on how permeable rock is at the surface.
Aquifer in the United States
Aquifers in Georgia
Springs and Wells Groundwater movement is determined by the slope of the water table. Moves down slope. If the water table reaches the Earth’s surface, water will flow out from the ground and will form a spring. Springs are an important source of drinking water. Where the water table is higher than the Earth’s surface, lakes will form.
Wells are human-made holes that are deeper than the level of the water table. If it is not deep enough, it will dry up when the water table falls below the bottom of the well. If an area has too many wells, groundwater can be removed too rapidly which can cause the wells to run dry.
Artesian Springs A sloping layer of permeable rock sandwiched between two layers of impermeable rock is called an artesian formation. The permeable rock is an aquifer and the top layer of impermeable rock is called a cap rock. Artesian spring is a spring whose water flows from a crack in the cap rock of the aquifer. These are sometimes found in deserts, where they are the only source of water. Most have cool water but some springs have hot water.
Formation of Caves Water erosion creates most caves found along coastal areas. Waves crashing against the rock over years wears away part of the rock forming a cave. Inland caves are also formed by water erosion-in particular, groundwater eroding limestone. As the limestone dissolves, underground passageways and caverns are formed.
The Caves of Belize Caves Branch Cave The Caves at Norman Island
Sinkholes Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by ground water circulating through them. As the rock dissolves, spaces and caverns develop underground. Sinkholes are dramatic because the land usually stays intact for a while until the underground spaces just get too big. If there is not enough support for the land above the spaces then a sudden collapse of the land surface can occur. The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.
Sinkhole - Guatemala 330 ft deep Nixa, Missouri 60 feet in diameter and 75 feet deep