1. Groundwater Water Beneath the Surface

2. Groundwater Largest freshwater reservoir for humans

3. Distribution of Groundwater Groundwater: Belt of soil moisture Zone of aeration Unsaturated zone Pore spaces in the material are filled mainly with air Zone of saturation –All pore spaces in the material are filled with water –Water within the pores is groundwater Water table – the upper limit of the zone of saturation

4. Features associated with subsurface water

5. Porosity Amount of pore space available Determines how much groundwater can be stored Depends on: Shape, packing and arrangement of grains Well-sorted: all grains are the same size (high porosity), examples: sand, poorly cemented coquina. Poorly-sorted: finer grains fill spaces between larger grains (low porosity), examples: well- cemented sandstone, shale, mudstone, and limestone.

6. Permeability Ability to transmit water through connected pore spaces How easily water can flow through a rock or sediment Depends on: Grain size (Coarser-grained sediments are more permeable than fine-grained sediments because the pores between the grains are larger) Grain shape and packing (sorting)

7. Features Associated with Groundwater Aquitard – an impermeable layer of material Aquifer – a permeable layer of material Springs Hot springs Water is 6-9ºC warmer than the mean air temperature of the locality Heated by cooling of igneous rock Geysers Intermittent hot springs Water turns to steam and erupts

8. Old Faithful geyser in Yellowstone National Park

9. Features Associated with Groundwater Wells Pumping can cause a drawdown (lowering) of the water table Pumping can form a cone of depression in the water table Artesian wells Water in the well rises higher than the initial groundwater level

10. Two Types of Aquifers Unconfined: water level rises freely as the aquifer recharges Confined: rising water reaches impermeable layer, becomes pressurized

11. Formation of a cone of depression in the water table

12. An artesian well resulting from an inclined aquifer

13. Environmental Problems Associated with Groundwater Treating it as a nonrenewable resource Land subsidence caused by its withdrawal Contamination

14. Geologic Work of Groundwater Groundwater is often mildly acidic Contains weak carbonic acid Dissolves calcite in limestone Caverns Formed by dissolving rock beneath Earth's surface Formed in the zone of saturation

15. Geologic Work of Groundwater Features found within caverns Form in the zone of aeration Composed of dripstone Calcite deposited as dripping water evaporates Common features include stalactites (hanging from the ceiling) and stalagmites (growing upward from the floor)

16. Dripstone formations in Carlsbad Caverns National Park

17. Karst topography Formed by dissolving rock at, or near, Earth's surface Common features Sinkholes – surface depressions Sinkholes form by dissolving bedrock and cavern collapse Caves and caverns Area lacks good surface drainage Geologic Work of Groundwater

18. Infrared image of karst topography in central Florida