Post on 01-Apr-2015
Chapter 16
GroundwaterWater beneath Earth’s surface
AquiferBody of rock or sediment that stores groundwater
Allows flow of groundwater
AquifersNeed porosity and permeabilityPorosity
Percentage of aquifer total volume that is open spaces
PermeabilityConnectivity of poresAllows water to flow through the rock
Aquifer ZonesZone of Saturation
Pore space completely filled with waterWater table – upper surface of this zone
Zone of AerationLies between water table & Earth’s surface
Water Table DepthDepends on
Surface topography (contours usually match local topography)
Permeability of aquiferRainfall amountRate of human use of water
Groundwater ReplenishmentMay replenish slower than it is usedRecharge zones
Area where water enters an aquiferSometimes labeled Near oceans, salt water can flow into an
aquifer if too much pumped
Wells & SpringsWells
Hole dug to the water table to get waterPumping water forms cone of depressionWell might run dry
Wells & SpringsSprings
Natural flow of groundwater to Earth’s surface where the ground dips below the water table
Usually found in rugged terrainCan dry up as water table changes
Artesian FormationSloping layer of permeable rock sandwiched
between 2 layers of impermeable rockCaprock – impermeable rock layersCan form artesian wellCone of depression: pumping water from the well lowers the water table around it
Artesian WellsWell through which water flows freely to the
Earth’s surface (in normal wells, it has to be pumped)
Artesian formation creates pressure to force water out of the ground
If caprock cracks, can get an artesian spring or well
In a normal aquifer, rock layers are horizontal and lack a cap. In an artesian formation, the permeable rock layer slopes and is covered by an impermeable layer called caprock.
Hot SpringsGroundwater passes near magma ands heats
up to above 37oCTravertine – mineral deposits from cooled hot
springsMud pots - muddy hot springs clayPaint pots – brightly colored clay
GeysersHot springs that periodically erupt from
surface pools or through small ventsSteam builds up underground and eventually
erupts through the vent when the pressure builds up
If there is no steam build up underground, there is no eruption (and therefore, no geyser).
Weathering by GroundwaterGroundwater passes through soil and other
organic minerals and forms carbonic acidGroundwater dissolves and breaks down
minerals in the rock
CavernsA large caveStalactites
Calcite deposited on cave ceilingStalagmite
Calcite deposited on cave floorColumn
Stalagmite meets stalagtiteHow caverns form: groundwater flows through
cracks & carbonic acid dissolves limestone and makes cracks bigger. This eventually makes a cavern.
Stalactite
Stalagmite
SinkholesCircular depression that forms at the surface
when rock dissolves , when sediment is removed, or when caves or mines collapse
Subsidence sinkholedepression in ground
Collapse sinkholeopen hole in the ground
Natural BridgesUncollapsed rock between 2 adjoining
sinkholes or when two sides of a cavern collapse
Karst TopographyType of topography characterized by
sinkholes, caverns, and underground drainage
Forms on LIMESTONE and other soluble rock