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ES 4.3 PPT
 

ES 4.3 PPT

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    ES 4.3 PPT ES 4.3 PPT Presentation Transcript

    • 4.3EARTH’S GROUNDWATER
    • Surface Water vs. Groundwater It’s obvious water exists on the surface of the Earth; evident by streams, lakes, and oceans.  However, a large amount flowing underground and beneath Earth’s surface is not visible to us. The water located within the rocks below the Earth’s surface is called groundwater.  Plays an important role in erosion and deposition as well.
    • Porosity The total volume of open space in a rock or sediment sample is known as porosity.
    • Permeability The ability of a rock or sediment sample to let fluids pass through its pores, or open spaces, is known as permeability.
    • The Water Table Through infiltration and percolation, surface water seeps underground and into the soil. As it travels underground, it passes through two distinct zones:  Zone of Aeration (upper zone)  Zone of Saturation (lower zone)  groundwater The boundary between the zone of aeration and the zone of saturation, which is the upper surface of underground water, is known as the water table.
    • The Water Table Wet seasons  The water table can be at or just beneath the soil’s surface. Dry seasons  The water table may be hundreds of meters beneath the ground.
    • Aquifers A body of rock or sediment storing groundwater and allowing the flow of groundwater is called an aquifer.  Described by its ability to hold water and its ability to allow water to pass freely through it (the zone of saturation).
    • Aquifers Two types of aquifers:  Unconfined: permeable rock unit replenished (recharged) directly by rainfall and surface water infiltrating/percolating down through and whose upper surface is the water table.  Confined: also known as “artesian”; a sloping layer of permeable rock sandwiched between two layers of impermeable rock and is exposed at the surface.
    • Recharge Zones Like rivers, aquifers depend on the water cycle to maintain a constant flow of water.  The ground surface where water enters an aquifer is called the recharge zone.  Size of the zone depends upon the permeability of the rock at its surface.
    • Wells A hole dug below the level of the water table in order to bring groundwater to Earth’s surface is called a well.  Must be drilled deep enough so when the water table drops, the well still contains water.  Pumping water from a well lowers the water table around the well and forms a cone of depression.  If too much water is taken from the well, it may drop below the level of the well and the well will go dry. An artesian well is a well through which water flows freely without being pumped.
    • Springs A spring is a natural flow of groundwater to Earth’s surface in places where the ground surface dips below the water table.  In a confined (artesian) aquifer, the top layer of impermeable rock is called the cap rock.  An artesian spring is a spring whose water flows from a crack in the cap rock of the aquifer. Most springs have cool water, but ones having water with a temperature of 37 ° Celsius which rises to the surface before cooling are called hot springs.  Can periodically erupt from surface pools through small vents  geysers. Old Faithful Geyser, Yellowstone National Park
    • Cave Erosion As water moves through the rocks of caves (mainly limestone), it combines with carbon dioxide (CO2) to produce carbonic acid (H2CO3).  This weak acid chemically weathers the rock by breaking down and dissolving minerals in the rock.
    • Cave Deposition Caves show signs of both erosion and deposition.  Water dripping from cracks in a cave’s ceiling leaves behind deposits of calcium carbonate. Sharp, icicle-shaped features forming on cave ceilings are known as stalactites. Water falling to the cave’s ground floor builds up to cone-shaped features known as stalagmites.
    • Cave Deposition Often, a stalactite and a stalagmite will grow until they meet, forming a calcite deposit known as a dripstone column.