Groundwater
What you need to learn
o
How large amounts of water are stored
underground
o
How groundwater dissolves limestone and forms
caves and other natural features
o
How groundwater is removed from the ground by
humans and what problems endanger our groundwater supply
Movement and Storage
o
Groundwater is present everywhere beneath the
surface of land, but is only a small fraction of all water on Earth
o
Hydrosphere: all the water on or in Earth
n
97% oceans 3%
by landmasses
n
90% of freshwater is found in ice
o
Ultimate source of water is in the oceans
How is groundwater stored?
o Water that doesn’t runoff the land is absorbed into
the ground by infiltration
o The porosity of a material determines how much water
it can hold
n Well sorted material contains around 30%
o Zone of Saturation: depth below the surface that all
the pores fill up with water
n The upper portion is called the water table
The Water Table
o Depth depends on local conditions
n It is shallow if there is a lot of surface water
o Changes with the topography
o Changes with the precipitation
Groundwater Movement
o
Flows downhill in the direction of the slope
o
The speed is extremely slow, but depends on the
materials permeability
o
Most ground water moves through permeable layers
called aquifers
o
Aquicludes: are
impermeable layers
Erosion and Deposition
o Groundwater is slightly acidic and can corrode
carbonate rocks (such as limestone)
o Caves are produced when groundwater dissolves
limestone
o Sinkholes are produced when caves or bedrock collapse
and sink the surface of the ground sinks
n Regions of sinking landscape are called karst topography
Groundwater Deposits
o Hard water: contains high concentrations of calcium
o Natural deposits: dripstone formations found in caves
n Stalactites: hang for cave ceiling
n Stalagmites: form on the cave floor
n Columns: form when they grow together
n Travertine: the type of limestone that makes them
Groundwater Systems
o Groundwater eventually reaches the surface after
hundreds of years
o Springs: natural discharges of groundwater
o The temperature of the water usually matches the area
and is colder in the summer and warmer in the winter
n Hot springs have temperatures above 98°
n Geysers are explosive hot springs
Wells
o Wells are holes dug or drilled deep into the ground to
an aquifer
n Overpumping of a well can cause drawdown where the water table
lowers
n Watertables can recharge with increased precipitation
n Aquifers that are under pressure are called Artesian
wells
Threats to our water supply
o Overuse
o Subsidence – the sinking of land
o Pollution – sewage, industrial waste, landfills, and
agricultural chemicals
o Chemicals
o Salt
o Radon – causes cancer