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1. PowerLecture A Microsoft® PowerPoint® Link Tool for Essentials of Physical Geology 5th Edition Reed Wicander  | James S. Monroe academic.cengage/com/earthsci

2. Chapter 13 Ground Water

3. Introduction • Groundwater is all subsurface water trapped in the pores and other open spaces in rocks, sediments, and soil. • Groundwater is responsible for forming beautiful caverns • It is also an important source of freshwater

4. Groundwater and the Hydrologic Cycle • Groundwater is part of the hydrologic cycle and an important natural resource. • As the world’s population and industrial development expand, the demand for water, particularly groundwater, will increase. • Most groundwater, in the United States, is used for irrigation and public drinking water supplies

5. Porosity and Permeability Groundwater is stored in open spaces in rocks called pores. Porosity is the percentage of a material’s total volume that is pore space. Permeability is the capacity to transmit fluids. This is necessary if we are to produce water from rocks. Permeability is dependent on porosity, but also on the size of the pores and their interconnections. Fig. 13.1a, p. 331

6. Porosity and Permeability • Types of Pores – some rock types have more porosity than others Table 13.1, p. 330 Figure 13.1, p. 331

7. The Water Table The water table is the top of the zone beneath the surface in which the pores are filled with water. Zone of aeration - when water initially infiltrates the ground, most of the pores are filled with air. Zone of saturation – underlying this is a zone in which the pores are filled with water. Fig. 13.2, p. 332

8. Groundwater Movement • Groundwater moves slowly downward under the influence of gravity through the zone of aeration to the zone of saturation. Fig. 13.3, p. 332

9. Groundwater Movement • Some of it moves along the surface of the water table, and the rest moves from areas of high pressure to areas of low pressure. Fig. 13.3, p. 332

10. Groundwater Movement • Groundwater velocity varies greatly and depends on various factors. Generally, the average velocity of groundwater is a few centimeters per day. Fig. 13.3, p. 332

11. Springs, Water Wells, and Artesian Systems • Springsare found wherever the water table intersects the surface. • When percolating water reaches the water or an impermeable layer, it flows laterally, and if this flow intersects the surface, water is discharged as a spring. Fig. 13.4, p. 333

12. Springs, Water Wells, and Artesian Systems • Water wellsare openings made by digging or drilling down into the zone of saturation. • When the zone of saturation has been penetrated, water percolates into the well, filling it to the level of the water table. Fig. 13.6, p. 335

13. Springs, Water Wells, and Artesian Systems • Artesian systems • In an artesian system, confined groundwater builds up high hydrostatic pressure. • For an artesian system to develop, three geologic conditions must be met: • 1. The aquifer must be confined above and below by aquicludes, layers that are not permeable. Fig. 13.6, p. 335

14. Springs, Water Wells, and Artesian Systems • 2. The aquifer is usually tilted and exposed at the surface so it can be recharged • 3. Precipitation must be sufficient to keep the aquifer filled. The dashed line defines the highest level the water can rise. If it does not rise all the way to the surface, it must be pumped out. Fig. 13.6, p. 335

15. Groundwater Erosion and Deposition • Sinkholes and Karst Topography • Sinkholes are depressions in the ground formed by the dissolution of the underlying soluble rocks or the collapse of a cave roof. Fig. 13.8 a-b, p. 338

16. Groundwater Erosion and Deposition • Karst topography largely develops by groundwater erosion in many areas underlain by soluble rocks. Fig. 13.9, p. 339

17. Groundwater Erosion and Deposition • Features of karst topography include: • Sinkholes, along with springs, solution valleys, disappearing streams, and caves. Fig. 13.9, p. 339

18. Groundwater Erosion and Deposition • Areas of the world exhibiting karst topography. Karst develops largely by solution of limestone. Fig. 13.7, p. 338

19. Groundwater Erosion and Deposition • Caves and Cave Depositsform when groundwater dissolves the soluble rock layers and they collapse. Fig. 13.11 a, p. 341

20. Groundwater Erosion and Deposition • The precipitation of calcite within caves creates a variety of interesting features. Fig. 13.12, p. 341

21. Groundwater Erosion and Deposition • Common cave deposits include: • Stalactites • Stalagmites • Columns • Drip Curtains • Travertine Fig. 13.11 c, p. 341

22. Modifications of the Groundwater System And Their Effects Modifications to the groundwater system can cause serious problems such as: Lowering of the water table Saltwater incursion Subsidence Contamination. • Groundwater is a valuable natural resource that is being exploited rapidly. Fig. 13.13, p. 342

23. Saltwater Incursion A problem in coastal areas Fig. 13.14, p. 343

24. Ocean Water table Fresh groundwater Salty groundwater Cone of depression Pumping well Ocean Water table Cone of ascension Fresh groundwater Pumping well Recharge well Ocean Water table Fresh groundwater Cone of depression Salty groundwater Salty groundwater Stepped Art Fig. 13-14, p. 343

25. Subsidence • When withdrawal from wells exceeds the rate of recharge, saltwater encroachment and ground subsidence may result. Fig. 13.15, p. 344 Fig. 13.16, p. 344 Fig. 13.17, p. 345

26. Modifications of the Groundwater System And Their Effects • Groundwater Contaminationby humans from landfills, septic systems, toxic waste sites, and industrial effluents is becoming a serious problem. Fig. 13.18 b, p. 348

27. Modifications of the Groundwater System And Their Effects • Groundwater Quality • Groundwater quality is mostly a function of • the kinds of materials that make up an aquifer • the residence time of water in an aquifer • the solubility of rocks and minerals. • These factors account for the amount of dissolved materials in groundwater and are responsible for such undesirable effects as hard water and iron staining.

28. Hydrothermal Activity Hydrothermal refers to hot water, typically heated by magma but also resulting from Earth’s geothermal gradient as it circulates deeply beneath the surface. Fumaroles, hot springs, and geysers are all hydrothermal features. Fig. 13.20, p. 349

29. Hydrothermal Activity Geysers and hot springs develop where groundwater is heated by hot subsurface rocks or the geothermal gradient. Hot springs - springs where the water temperature is higher than 37°C Fig. 13.19 a, p. 349

30. Hydrothermal Activity • Hot springs • Travertine and tufa - Precipitation of calcite from supersaturated hot spring water • Yellowstone National Park. Fig. 13.23 a, p. 351

31. Hydrothermal Activity • Geysers • hot springs which periodically eject hot water and steam with tremendous force. Fig. 13.22, p. 350

32. Hydrothermal Activity Fig. 13.19 b, p. 349 Fig. 13.21, p. 350

33. Geothermal Energy • Geothermal energy is energy produced from Earth’s internal heat • Comes from the steam and hot water trapped within Earth’s crust. • It is a relatively clean form of energy that is used as a source of heat and to generate electricity. • 1-2% of the world’s energy needs could be met with geothermal energy. • Derived from mostly convergent zones and hot spots Fig. 13.24, p.352

34. End of Chapter 13