Groundwater & Karst Topography Flashcards
Hydrologic Cycle
1) series of storage areas connected by transfer processes + closed/circular system
2) water can cycle through in hours or millions years
3) 99% Earth’s water in storage = oceans, lakes, rivers, ice, aquifers
4) only 2.8% freshwater AND 75% of that water is in glaciers
Describe evaporation precipitation balance
1) over the course of years it does balance + cancel each other out
2) tends to be more evaporation compared to precip over ocean, opposite true for continents
Residence times
amount of time water spends in a certain substance/medium
- may stay stored in ocean or lake for thousands of years
groundwater
1) underground water in subsurface zone where pore spaces completely filled with water (zone of saturation)
2) more than 50% of world’s groundwater within .5 miles underground
source of groundwater
majority of groundwater comes as precipitation from above that percolated into soil or seeped downward from lakes
Porosity
1) quantity of water that can be held in subsurface material
2) more porous = more open space/cracks = more water stored
permeability
1) ability for water to move through soil
2) means the holes/cracks connected
Rate at which water moves through rocks depends on
1) permeability
2) porosity
ex = clay has many small interstices that give it high porosity BUT the interstices bind so strongly to water that water cannot move through it
aquifers
1) PERMEABLE ROCK where water is stored in sediment underground
2) 3 layers = zone of aeration, zone of saturation, waterless zone
aquicludes
1) impermeable materials composed of components like clay which hinder water movement
2) ex = clay + bedrock
3 hydrologic zones for groundwater
1) zone of aeration
2) zone of saturation
3) waterless zone
Zone of aeration
1) mixture of solids, water, air
2) depth varies
3) interstices filled with water + air
4) water that isn’t held by molecular attraction seeps down
zone of saturation
1) pores fully saturated with water
2) water table = top of saturated zone
3) watertable bends to surface above + when it intersects with land –> forms spring
4) humid regions = high water table
Cone of depression
1) well filled with water up to water table
2) if water is taken out faster than flows into saturated rock –> creates a “cone of depression” where no water
Types of aquifers
1) unconfined (able to enter from any location)
2) confined (only able to fill from one location)
How do lakes relate to watertables
Lakes usually depressions that go deep enough into water table
confined aquifers
1) when aquifer is confined by acquicludes above + below
2) tends to have a sloping/dipping layer where it absorbs infiltrating water
artesian wells
1) when you drill a well into a confined aquifer –> pressure forces water to rise
2) if water rises up to surface = called a artesian well
3) if water only partially rises upward = subartesian
piezometric surface
elevation to which water in artesian well rises
Groundwater pollution
1) if pollution seeps into aquifer = may remain indefinitely
waterless zone
low limit of zone of saturation lacks pore spaces –> has no water
Groundwater mining problems
1) groundwater accumulates very slowly (.5 cm/year) but humans tap water very quickly (75 cm/year)
2) can cause subsidence (sinking of land)
Fossil water
1) groundwater considered nonrenewable resource
Dissolution
removal of bedrock through chemical weathering + action of water
Role of Bedrock in dissolution
Joints + bedding planes allow groundwater to penetrate rock easily –> resulting in more water which can dissolve calcium bicarb
Precipitation
1) Hot springs + geysers provide accumulation of precipitated materials
2) Hot water (heated by magma) dissolves more
Caverns
open areas created by dissolution along joints + bedding planes
Speleothems
formed by precipitation bc water leaves behind compounds (carbon dioxide + calcite)
stalactite = on roof, stalagmite = on bottom
Cave formation steps
1) cavern formed by dissolution when percolating water dissolves carbonate bedrock
2) decoration stage = formation of spleothems (precip occurs when you remove h20 or co2 from calcium limestone water slurry)
Where does cave formation occur
1) mainly in tropical climates because it has water + good drainage in soils
Karst landforms
1) typical landforms in karst regions are sinkholes, disrupted surface drainage, underground drainage networks
2) form where there is massive LIMESTONE bedrock water air
Denudation cycle of Karst
1) weathering = chemical + carbonation
2) no mass wasting (since it’s not going downward anywhere)
3) erosion = (pickup, transport, deposition) precipitation
SO ITS BASICALLY
1) dissolution caused by carbonic acid (formed by water + co2)
2) precipitation (carbonic acid breaks down carbonate rocks like limestone) to form calcium bicarb that dissolves in water
Sinkholes
1) rounded depressions formed by dissolution of carbonate rocks (shallow limestone)
2) collapse sinkhole = result of sediment over limestone + limestone breaks away + causes sudden collapse
Effect of sinkholes on drainage
1) channel surface runoff into groundwater circulation
2) creates uvala = chain of intersecting sinkholes
3) disappearing streams = surface runoff disappears into sinkhole/crack
Tower karst
residual karst features –> steep hills caused by intense rainfall that contributes to dissolution around base of hills
Mogotes + haystack hills
limestone dissolved away (late stage karst) + leaves behind massive haystack hills
Hydrothermal activity
where hot water comes to surface through natural openings
Hot springs
1) hot water at earth’s surface = indicates that water has come into contact with heated rocks + magma
2) sloping land = forms terraces
3) flat land = forms deposits
Geysers
1) special intermittent hot spring
2) water accumulates in deep reservoirs, heats to 200 C without boiling (due to high pressure above it) and suddenly surges upward creating an eruption
Fumarole
1) surface crack directly connected to deep-seated heat source
2) when water drains into it, forms a cloud of steam
3) essentially hot spring without water
4) can become a mudpot
