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)