Groundwater is one of our most valuable resources, although you probably never see it or do not even realize that it is there. Groundwater can appear in various ways and one of them is in aquifers. In fact, there is an immense amount of water in aquifers under the surface of the Earth. Possibly there may be more than a hundred times more water in the subsoil than in all rivers and lakes in the world. But for these aquifers to be formed, special conditions have to occur.
If you want to know What is an aquifer: definition and how it is formed In ecology, we tell you everything.
What is an aquifer
According to its etymological origin, aquifer It comes from the Latin “aqua” which means “water” and “fierce” which literally means “I carry”, so in Latin it literally means “I carry water.” In terms of geology, an aquifer is a underground geological formation that houses water. The aquifers allow the passage of water through fissures and cracks in the rocks to such an extent that sometimes, the water can reach the earth’s surface and other surface water masses.
In aquifers several key areas are differentiated: The water table, the saturation zone and the waterproof layer. The water table is the level where the water is located and corresponds to the upper sector. The saturation zone is the space where the pores of the rocks that can be flooded when the water table increases. Finally, there is the waterproof layer that is the rock layer that allows water to accumulate and move horizontally and vertically. Between the water table and the surface there may be another area known as a airing zone.
How an aquifer is formed
Groundwater is another part of the Water cycle. Part of the rainfall infiltrate the subsoil and descend until they reach the rock material underneath. Rocky material can be more or less permeable; If it is permeable, it will let the water pass, but if the passage of water is impervious, it will be interrupted and will be accumulated.
Two important factors intervene in the training of groundwater and aquifers:
- Gravity: Gravity attracts water to the center of the Earth, so the water that falls on the surface will try to filter towards the subsoil.
- Lithology: The rock under the surface of the Earth influences the formation of aquifers. If all the mother rock consists of a dense material even gravity cannot make the water filter. The mother rock also contains variable amounts of empty spaces where groundwater accumulates and can also be broken by creating more spaces. On the other hand, when the mother rock is limestone, the water dissolves the rock and as a result large cavities that are filled with water are obtained.
However intense the strength of gravity is not to drag all the water below. In the depth of the earth’s crust there are materials such as granite or clays that prevent water from crossing them. In many cases these layers are located below others that do let the water pass and, therefore, act as a layer of confinement of groundwater. Since it is more difficult for water to deepen, it tends to accumulate in the porous layers and slowly flow in a more horizontal direction (parallel to the rock layers) towards the surface.
Precipitation eventually recharges the aquifer. However, the recharge rate is not the same for all aquifers, and that should be considered when water is extracted from a well. Pumping too much water in a short term space can cause its exhaustion if rainfall does not recharge the aquifer enough.
Types of aquifers
Aquifers can be classified In different ways according to what characteristics.
Structure
According to their structure, three types of Aquifers: free, confined and semiconfined. Free aquifers are those in which there is a water table, that is, a level to which the water is found in the subsoil. That level is determined by the place where the waterproof layer is located in the subsoil and where the earth’s surface is located. In some cases the water table can reach the surface and then originate springs, wetlands, streams or other bodies of water.
On the other hand, confined aquifers are those in which groundwater is stored under pressure due to the existence of several layers of waterproof rocks. Sometimes the rock layers bend or lean inside the earth’s crust and this can cause a layer of rock less porous to be both above and below the porous layer confining the water inside. In this case, the rocks surrounding the aquifer limit pressure on the porous rock and its water. In these aquifers, the pressure, called artsian pressure, is greater than atmospheric. Consequently, if a well is drilled in this “pressurized” aquifer, internal pressure could be sufficient (depending on the rock capacity to transport water) to push the water into the well and the surface.
Finally, in semiconfined aquifers, permeability is intermediate but pressure is equal to atmospheric.
Porosity
According to their porosity they can be classified as porous and fisural aquifers. Porous aquifers have numerous interconnected pores where water accumulates. They are not too permeable and in this category you can find clay formations or alluvial gravels. Fisural aquifers are characterized by the existence of fissures in the rock, also interconnected but that allow a better passage of water. These are the best known aquifers and for example are those that occur in karst areas.
Lithology
They can also be classified according to their lithology or type of rock on which it has been formed, but in this case there may be hundreds of types of aquifers. They can settle, for example, on limestone rocks (karst landscape), sandstones or volcanic stones.
Water behavior
According to water behavior, they can be differentiated into four types: aquifers, aquitors, aquícludos and aquifugos. Aquifers can be considered as stores and groundwater transmitters. Acuitrados are good stores, but bad transmitters, aquyluds are only transmitters and aquifuges do not allow storage or water transmission.
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