Aquifer facts for kids
An aquifer is a special underground layer of rock or soil that holds water. Think of it like a giant sponge deep in the ground! This layer can be made of things like sand, gravel, clay, or even certain types of rock. The important thing is that water can easily flow into and through it.
People can get this underground water, also called groundwater, by digging a well. The science of studying how water moves in aquifers is called hydrogeology.
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How Water Stays in Rocks
Sometimes, groundwater can flow in underground rivers, like in caves. This often happens in places with limestone that has been eroded away. These areas are called karst topography. However, these are rare.
More often, the tiny spaces inside rocks underground are simply filled with water. Imagine a kitchen sponge that is full of water. This water can then be pumped out for farms, factories, or cities to use.
Porosity and Permeability
For a rock layer to be a good aquifer, it needs to let water pass through it. This is called permeability. Even if a rock has many tiny holes (which is called porosity), it might not be a good aquifer if the holes are not connected. Water needs to be able to move from one hole to the next.
For example, some rocks might have lots of tiny spaces, but if water can't easily flow through them, they won't make good aquifers. However, if a rock has many cracks or fissures, water can flow through those cracks, making it a good aquifer.
Big Aquifers Around the World
There are many huge aquifers across the globe that provide water to millions of people. Here are some of the most famous ones:
- The Great Artesian Basin in Australia is one of the largest aquifers in the world. It covers over 1.7 million square kilometers! It's a very important source of water for Queensland and remote parts of South Australia.
- The Guarani Aquifer is shared by four countries: Brazil, Argentina, Paraguay, and Uruguay. It covers a huge area of 1.2 million square kilometers.
- The Ogallala Aquifer in the central United States is another giant aquifer. It lies under parts of eight different states. Much of its water is very old, from the time of the last ice age.
- The Nubian Sandstone Aquifer System (NSAS) is the biggest known aquifer system in the world that holds ancient, or "fossil," water.
Using Aquifers for Water
Aquifers can be found at different depths underground. Those closer to the surface are often used for water supply and irrigation (watering crops). These shallow aquifers are also more likely to be refilled by local rainfall. Many desert areas have limestone hills nearby that can be used as sources of groundwater.
Sometimes, people take out more water from an aquifer than can naturally flow back in. This is called over-harvesting. In some coastal areas, like Libya and Israel, too many people using the water has caused the water level in aquifers to drop. When this happens, saltwater from the sea can seep into the aquifer, making the water salty and unusable.
When water slowly comes out of the ground on its own, it's called a seep or a "spring (water)". This usually means there's an aquifer underneath.
Images for kids
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Water in porous aquifers slowly seeps through pore spaces between sand grains
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Water in karst aquifers flows through open conduits where water flows as underground streams
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Map of major US aquifers by rock type
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Texas blind salamander found in Edwards Aquifer
