chapter 16. groundwater water beneath earth’s surface aquifer body of rock or sediment that stores...

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