Geology Chapter 13

Ground Water

-Resource (domestic, industrial and agricultural use)
-Erosional agent
-Energy source in some areas (when heated by volcano)

Where can ground water be found

occurs everywhere beneath the Earth's surface, but its usually restricted to depths less than about 1000 meters

Porosity

How much empty space in the ground
-air, water, or oil/gas
-expressed as a percentage of the total rock volume
-circular, lots of room
-cubes not much room

Porosity dependent on

-size
-shape
-sorting
-arrangement

Permeability

How easy fluid can flow through rock

The Water Table

-vadose zone
-water table (middle of ground)
-Saturated zone- pull water out of pore space

Capillary fringe

little water coming up water table because water molecules are attracted to solid material

perched water table

when water is stuck at the water table because there is a lower porosity or permeability in that particular area. Create springs

confined and unconfined aquicludes

confined-- locked in by aquitard
unconfined-- open at top (at surface)

Ground water flow

measurement of the rate of flow with dye ,
can measure distance, time, etc

Rates of flow

-as fast as 250meteres/day (about a mile in 8 days) in high permeability material (very fast)
-a few cm/day is typical for most aquifers
-as slow as cm per year in nearly impermeable material (aquicludes) such as unfractured shale
-some rocks, sucha as sa

Cone of depresstion

crated by well
pulls water down, must allow time to recharge
can dry out someone else's well

Artesian springs and wells

-confined aquifers may create situations where teh "artesian pressure surface" is abouve level of ground
-water will flow natural to the surface without pumping. it may fountain

Springs

Recharge- addition of water
Discharge- spring

Contamination of Groundwater

-pesticides
-herbicides
-fertilizers
-pollutants leached by rainwater
-bacteria , viruses, parasites
-mine waste

Land subsidence

caused by compaction due to groundwater withdrawal
loose grains are packed tighter
Venice- used to have roads

Caves and Karst Topography

features that are created when water dissolves bedrock
limestone only!

Karst Topography

Surface expression of karst
sink holes (a cavern roof falls in)

Caves and Cave Deposits

may have a complex history reflecting changes in the water table

Stalactites

rods of calcium carbonate

Hot spring

higher than human temperature (37c or 98f)
can deposit CaCO2 or silica

Geyser

an intermittent surface emission of hot water and steam

Where does hydrothermal activity occur?

hot springs
geysers

Formation of a geyser

erupt as water comes to boiling point
triggered by increase in temperature or drop in pressure
(old faithful)