1. Water Under the Ground Chapter 12 Water On and Under the Ground Geology Today Barbara W. Murck Brian J. Skinner N. Lindsley-Griffin, 1999 Lutgens & Tarbuck, J.R. Griffin, 1999 Carlsbad Caverns, NM

2. The Water Table Water Table = Top surface of the saturated zone Zone of aeration (unsaturated zone) - pores filled with air Saturated zone - pores filled with water N. Lindsley-Griffin, 1999 Fig. 12.22 p. 353

3. How Groundwater Moves N. Lindsley-Griffin, 1999 Fig. 12.24, p. 355

4. N. Lindsley-Griffin, 1999 A stream that lies above the water table loses water to the zone of saturation, will dry up at times. A stream that lies below the water table receives water from zone of saturation, will flow all year. Groundwater and Streams

5. Porosity and Permeability Porosity - percentage of total volume of rock that consists of open spaces (pores). (how many pores, and how big they are) Permeability - a measure of how easily a solid allows fluids to pass through it. (how well connected the pores are) N. Lindsley-Griffin, 1999 Fig. 12.23 p. 354

6. Porosity and Permeability IN GENERAL - Porosity and permeability are better in: well sorted sediments loosely packed sediments spherical sediments Cementation of sediment decreases both porosity and permeability N. Lindsley-Griffin, 1999 Low PorosityHigh Porosity Poorly sorted Well sorted Tightly packedLoosely packed NonsphericalSpherical

7. Aquifers Aquifer - a body of water-saturated, porous and permeable, rock or regolith N. Lindsley-Griffin, 1999 Fig. 12.26 p. 358

8. Aquifers Confined aquifer: trapped between impermeable layers (aquicludes). Unconfined aquifer: top of saturation zone is water table N. Lindsley-Griffin, 1999 Fig. 12.26, p. 358

9. Recharge Recharge - replenishment of groundwater Recharge zone - where groundwater is replenished by infiltration of rainfall and snowfall, which percolates downward to the saturated zone. N. Lindsley-Griffin, 1999 Fig. 12.26, p. 358

10. Discharge Discharge - process by which groundwater returns to the surface. Examples: streams, springs, wells, the ocean. N. Lindsley-Griffin, 1999

11. Wells Pumping produces a cone of depression in the water table around the well. Fig. 12.29, p. 360 N. Lindsley-Griffin, 1999

12. ArtesianWells Artesian system: water pushed up to water table by hydraulic pressure. Requires a confined aquifer, and sufficient pressure. Usually supplied by folded or faulted beds that surface at a higher elevation in the recharge area. N. Lindsley-Griffin, 1999 Fig. 12.27 p. 359

13. Sources of Groundwater Contamination Leaching of toxic chemicals from unlined landfills. Leaking septic tanks. Agricultural chemicals. LUST (Leaking Underground Storage Tanks) N. Lindsley-Griffin, 1999 Fig.12.30, p. 361

14. Springs Springs form where a change in rock permeability forces groundwater out to the surface: a) limestone over shale. N. Lindsley-Griffin, 1999 Fig. 12.28, p. 359

15. Springs Springs form… b) highly jointed permeable rock like a lava flow over impermeable limestone, or c) along a fault. N. Lindsley-Griffin, 1999 Fig. 12.28, p. 359

16. Springs Springs form… c) along a fault, - where a permeable layer is blocked by being moved against an impermeable layer, - or where the fault itself is impermeable. N. Lindsley-Griffin, 1999 Fig. 9.11, p. 251

17. Caves and Caverns Caves and caverns - underground open spaces - form by dissolution of carbonate rocks near the top of a seasonally fluctuating water table. They are closed to the surface or have only a small opening. Fig. 12.25 B, p. 357 N. Lindsley-Griffin, 1999

18. Caves and Caverns Underground cavities form when water table is high, then fill with air when water table drops and water drains out. Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999 Earlier water table Present water table

19. Caves and Caverns After water table drops, percolation of acidic water from the surface dissolves ions which precipitate as calcite cave decorations in the open air of the cave. Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999 Earlier water table Present water table

20. Sinkholes Sinkholes are dissolution cavities that are open to the sky. They form by collapse of cave roofs or where rainwater is rich in carbon dioxide N. Lindsley-Griffin, 1999 Winter Park sinkhole, near Orlando FL - May 8-9, 1981 Grew to >100 m wide in 17 hours. Fig. 12.25 C, p. 357

21. Karst Extensive dissolution produces karst topography, with many small closed basins and sinkholes, and disrupted drainage. (Fig. 12.25A, p. 356) N. Lindsley-Griffin, 1999

22. Karst Prolonged development of karst results in topography with jagged carbonate towers that served as the inspiration for Chinese scroll painting. Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999 Limestone towers Auilin, China

23. Cave - a natural cavity below Earth’s surface Caves in limestone form by dissolution... below the water table. N. Lindsley-Griffin, 1998

24. “Soda Straws” Cave decorations form by precipitation above the water table

25. Sinkholes form when a cave roof collapses

26. Fossilization Groundwater aids fossilization by leaching away organic matter and depositing silica or carbonate ions Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999 Petrified Forest, AZ

27. Hot Springs and Geysers Hot springs form where groundwater heated by subsurface magma rises to the surface. Geysers (1) are eruptions of hot water caused when groundwater confined in subsurface fissures becomes superheated. Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999

28. N. Lindsley-Griffin, 1999 Hot Springs and Geysers Geysers (2) Superheated water at depth expands, causing water to slop over the rim and releasing the confining pressure. (3) Water “flashes” into steam and the geyser erupts.

29. Hot spring deposits form by precipitation of dissolved ions as the water cools