Post on 06-Apr-2018
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Groundwater
Groundwater contamination
Groundwater chemistry
Karst
Caves
Monroe & Wicander p. 330-335
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Groundwater Contamination
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Groundwater Contamination
Contaminated groundwater moves away fromsource of contamination in a contaminant plume
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Groundwater Contamination
Can map contaminant
plume Trace plume back to
source ofcontamination
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Groundwater Remediation
Dilution is one option
Removal is anotheroption
Removal typically byinjection and pumping
Sometimes removalby biological agents
(bioremediation) All of this is
EXPENSIVE!
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Groundwater Chemistry
Recall that dissolvedcarbon dioxide inwater creates a weak
acid carbonic acid Groundwater contains
mostly dissolvedsulfates and
bicarbonates of Ca,Mg, Na, K and Fe
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Groundwater Chemistry
Amount (andcomposition) of dissolvedmaterial in water dependson rocks the water flows
through
Hard water contains lotsof dissolve material
Soft water contains little
dissolved material
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Groundwater as a Geologic Agent
Creates distinctlandscapes in regionssusceptible to
chemical weathering Karst landscapes
created bydissolution-
precipitation reactions
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Karst
Dissolution
Limestones,dolostones and
marbles react mostreadily
Weathering results innear total removal ofcarbonate rock overtime
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Karst
Cementation
Groundwatereventually becomes
saturated with certainions (e.g. Ca, Mg, Si)
These materialsbecome precipitated
as cements betweenmineral grainselsewhere
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Karst
Replacement
Less commonprocess where water
dissolves matteralready present and ,at the same time,deposits from solutionan equal volume of adifferent substance
(e.g. petrified wood)
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Karst
Caves
Come in all sizes
Interconnected cavechambers andsystems called
caverns Form cave networks
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Cave Networks
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Cave Formation
Dissolution along joints or bedding planes nearwater table
Enlargement of passage(s) along most favorable
water flow route
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Evolution of Cave Systems
Rates of formation depend on acidity ofgroundwater, and water flow rates
~ 10,000 years to develop a continuous passage
~ 1,000,000 years to develop a cave system
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Caves
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Cave Deposits
Caves containprecipitates calleddripstones
Accumulations ofdripstone are calledspeleothems
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Cave Deposits
Stalactites are like carbonate icicles
Stalagmites project upward from cave floors
These two features may join to form columns
Also get soda straws, curtains
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Cave Deposits
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Spelunkers
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Sinkholes
Large dissolutioncavities open to thesurface
Some form as resultof cave roof collapse
Many result fromlowering of watertables
Can be a big problem!
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Karst Landscapes
Evolve over time bydissolution oflimestone landscapes
Some characteristicfeatures include:sinkholes, naturalbridges, disappearing
streams, blind valleys
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Karst Landscapes
Cone Karst
Tower Karst