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PowerLecture A Microsoft® PowerPoint® Link Tool for. Essentials of Physical Geology 5 th Edition Reed Wicander  | James S. Monroe. academic.cengage/com/earthsci. Chapter 13. Ground Water. Introduction.

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Powerlecture a microsoft powerpoint link tool for

PowerLecture

A Microsoft® PowerPoint® Link Tool

for

Essentials of Physical Geology

5th Edition

Reed Wicander  | James S. Monroe

academic.cengage/com/earthsci


Chapter 13

Chapter 13

Ground Water


Introduction

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


Groundwater and the hydrologic cycle

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


Porosity and permeability

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


Porosity and permeability1

Porosity and Permeability

  • Types of Pores – some rock types have more porosity than others

Table 13.1, p. 330

Figure 13.1, p. 331


The water table

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


Groundwater movement

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


Groundwater movement1

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


Groundwater movement2

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


Springs water wells and artesian systems

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


Springs water wells and artesian systems1

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


Springs water wells and artesian systems2

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


Springs water wells and artesian systems3

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


Groundwater erosion and deposition

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


Groundwater erosion and deposition1

Groundwater Erosion and Deposition

  • Karst topography largely develops by groundwater erosion in many areas underlain by soluble rocks.

Fig. 13.9, p. 339


Groundwater erosion and deposition2

Groundwater Erosion and Deposition

  • Features of karst topography include:

    • Sinkholes, along with springs, solution valleys, disappearing streams, and caves.

Fig. 13.9, p. 339


Groundwater erosion and deposition3

Groundwater Erosion and Deposition

  • Areas of the world exhibiting karst topography. Karst develops largely by solution of limestone.

Fig. 13.7, p. 338


Groundwater erosion and deposition4

Groundwater Erosion and Deposition

  • Caves and Cave Depositsform when groundwater dissolves the soluble rock layers and they collapse.

Fig. 13.11 a, p. 341


Groundwater erosion and deposition5

Groundwater Erosion and Deposition

  • The precipitation of calcite within caves creates a variety of interesting features.

Fig. 13.12, p. 341


Groundwater erosion and deposition6

Groundwater Erosion and Deposition

  • Common cave deposits include:

    • Stalactites

    • Stalagmites

    • Columns

    • Drip Curtains

    • Travertine

Fig. 13.11 c, p. 341


Modifications of the groundwater system and their effects

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


Saltwater incursion a problem in coastal areas

Saltwater Incursion A problem in coastal areas

Fig. 13.14, p. 343


Powerlecture a microsoft powerpoint link tool for

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


Subsidence

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


Modifications of the groundwater system and their effects1

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


Modifications of the groundwater system and their effects2

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.


Hydrothermal activity

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


Hydrothermal activity1

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


Hydrothermal activity2

Hydrothermal Activity

  • Hot springs

  • Travertine and tufa - Precipitation of calcite from supersaturated hot spring water

    • Yellowstone National Park.

Fig. 13.23 a, p. 351


Hydrothermal activity3

Hydrothermal Activity

  • Geysers

    • hot springs which periodically eject hot water and steam with tremendous force.

Fig. 13.22, p. 350


Hydrothermal activity4

Hydrothermal Activity

Fig. 13.19 b, p. 349

Fig. 13.21, p. 350


Geothermal energy

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


End of chapter 13

End of Chapter 13


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