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Why can water infiltrate the subsurface in solid bedrock?
Solid bedrock contains pore spaces
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What are the four types of pore spaces or voids in rocks?
spaces between mineral grains, fractures, solution cavities, and vesicles
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All rocks are cut by what?
fractures
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In some dense rocks (like granite), ______ are the only significant pore spaces.
fractures
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Permeability is what?
the capacity of a rock to TRANSMIT a fluid
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Permeability varies with what four things?
the fluid's viscosity, hydrostatic pressure, the size of openings, and the degree to which the openings are interconnected.
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How can a rock be highly porous and still have low permeability?
Is the pore spaces are very small, a rock have high porosity but low permeability because it is difficult for water to move through small openings.
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Rocks that commonly have high permeability are what? (hint: five rock types)
conglomerate, sandstones, basalts, and certain limestones
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Why is permeability high in sandstones and conglomerates?
the relatively large, interconnected pore spaces between grains
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Why is permeability high in basalt?
it is often extensively fractured by columnar jointing and because the tops of most flows are vesicular
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______ limestones are permeable.
Fractured
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What rocks have low permeability?
Shale, unfractured granite, quartzite, and other dense, crystalline metamorphic rocks.
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The water table is located where?
between the zone of aeration and saturation, on the upper surface of the zone of saturation
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The zone in which pore space is filled partly with air and partly with water, is the zone of-
zone of aeration
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The zone where all of the openings in the rock are completely filled with water is teh zone of-
zone of saturation
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Where impermeable layers occur within the zone of aeration, the groundwater is trapped above the general water table, forming a local what?
perched water table
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A permeable zone of or formation that is saturated with water is known as a what?
aquifer
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Aquifers are filled, or _____, as surface water seeps downward through the zone of aeration.
recharged
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Groundwater moves from zones of ____ pressure to zones of ____ pressure.
high; lower
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In a confined aquifer, the difference in elevation between parts of the water table in know as the what?
hydraulic head
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Natural discharge of the groundwater reservoir occurs where?
wherever the water table intersects the surface of the ground
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How are ordinary wells made?
by digging or drilling holes through the zone of aeration into the zone of saturation
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Describe how a cone of depression is formed.
when a well is pumped, the water table is drawn down around the well in the shape of a cone
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If water is withdrawn faster than it can be replenished, the cone of depression continues to grow. What will happen to the well?
it will go dry
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What are the three necessary geologic conditions for an artesian system?
- 1.a permeable bed (aquifer) confined between impermeable layers
- 2. rocks tilted so the aquifer can receive infiltration from surface water
- 3. adequate infiltration to fill the aquifer and create hydrostatic pressure
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The line of artesian-pressure surface shows what?
the height to which artesian water rises above the aquifer
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What three required conditions do geysers need for their development?
- 1. a body of hot rocks must lie close to the surface
- 2. a system of fractures must extend downward from the surface
- 3. a relatively large supply of groundwater must be present
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What is the cycle for eruptions of geysers?
The groundwater involved in geyser eruptions is under great pressure, rising the temperature. Because the water at the base of the fracture is under greater pressure then the water above, it must be heated to a higher temperature before it boils. When a slight increase in temperature or decrease in pressure happens it causes the deeper water to boil. The expanding steam throws water from the underground chambers high into the air. After the pressure is released, the caverns refill with water and the process is repeated.
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Why do geysers erupt in cycles?
Geysers must wait for the groundwater to refill after a eruption before it begins its process again.
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Geothermal energy is the thermal energy of-
groundwater
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How do sinkholes form?
Groundwater erodes fractures, expanding them into caves. As the caves grow larger it cannot sustain its roof and the ceiling collapses into a crater like depression
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Where sinkholes grow and enlarge, they merge and form elongate or irregular closed depressions known as-
solution valleys
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Small streams commonly flow on the surface for only a short distance and then disappear into a sinkhole, becoming a -?
disappearing stream
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Tower karst develop in what areas?
tropical
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Name the three main processes of the evolution of karst topography.
- 1. the enlargement of caves and the development of sinkholes
- 2. the enlargement of sinkholes and the development of solution valleys
- 3. the enlargement of solution valleys until the original limestone terrain is completely destroyed
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The tower karst in souther China are well developed because of the high _____ and thick layers of _______ exposed at the surface.
rainfall; limestone
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Define speleothems.
all the deposits that form in caves
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How do stalactites form? (Hint: Notice this is different from stalagmites)
As water enters a cave, carbon dioxide escapes during evaporation, and a small amount of calcium carbonate crystallizes. Each succeeding drop adds more calcium carbonate, so that eventually a cylindrical, or cone-shaped, projection is built downward from the ceiling
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How do stalagmites form? (Hint: Notice that this is different from stalactites)
The water-dripping from stalacite precipitates additional calcium carbonate onto the floor directly below.
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Stalactites and stalagmites unite to form what?
columns
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Changes in the chemical composition of groundwater, saltwater encroachment, changes in the position of the water table, and subsidence are all problems from what and effect what?
problems from human activities that alter the groundwater system
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