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Lecture Outlines PowerPoint
Chapter 5 Earth Science, 12e Tarbuck/Lutgens © 2009 Pearson Prentice Hall This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials.
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Running Water and Groundwater Chapter 5
Earth Science, 12e Running Water and Groundwater Chapter 5
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Earth as a system: the hydrologic cycle
Illustrates the circulation of Earth’s water supply Processes involved in the cycle Precipitation Evaporation Infiltration Runoff Transpiration
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The hydrologic cycle Figure 5.3
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Sources of Earth’s water
Figure 5.2
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Running water Drainage basin
Land area that contributes water to a river system A divide separates drainage basins
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Drainage basins and drainage divides
Figure 5.4
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Running water Streamflow Factors that determine velocity
Gradient, or slope Channel characteristics Shape Size Roughness Discharge – volume of water flowing in the stream (generally expressed as cubic feet per second)
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Running water Upstream-downstream changes Profile
Cross-sectional view of a stream From head (source) to mouth Profile is a smooth curve Gradient decreases from the head to the mouth Factors that increase downstream Velocity Discharge
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Running water Upstream-downstream changes Profile
Factors that increase downstream Channel size Factors that decrease downstream Gradient, or slope Channel roughness
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Longitudinal profile of a stream
Figure 5.7
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Running water The work of streams Erosion Transportation
Transported material is called the stream’s load Dissolved load Suspended load Bed load
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Running water The work of streams Transportation
Load is related to a stream’s Competence – maximum particle size Capacity – maximum load Capacity is related to discharge
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Running water The work of streams Transportation Deposition
Caused by a decrease in velocity Competence is reduced Sediment begins to drop out Stream sediments Known as alluvium Well-sorted deposits
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Running water The work of streams Transportation
Features produced by deposition Deltas – exist in ocean or lakes Natural levees – Form parallel to the stream channel Area behind the levees may contain backswamps or yazoo tributaries
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Formation of natural levees by repeated flooding
Figure 5.21
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Running water Base level Lowest point to which a stream can erode
Two general types Ultimate – sea level Temporary, or local Changing causes readjustment of the stream – deposition or erosion
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Adjustment of base level to changing conditions
Figure 5.15
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Running water Stream valleys Valley sides are shaped by
Weathering Overland flow Mass wasting Characteristics of narrow valleys V-shaped Downcutting toward base level
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Running water Stream valleys Characteristics of narrow valleys
Features often include Rapids Waterfalls Characteristics of wide valleys Stream is near base level Downward erosion is less dominant Stream energy is directed from side to side
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A narrow, V-shaped valley
Figure 5.17 A
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Continued erosion and deposition widens the valley
Figure 5.17 B
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A wide stream valley is characterized by meandering on a well-developed floodplain
Figure 5.17 C
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Running water Stream valleys Characteristics of wide valleys
Floodplain Features often include Meanders Cutoffs Oxbow lakes
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Erosion and deposition along a meandering stream
Figure 5.10
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A meander loop on the Colorado River
Figure 5.18
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Formation of a cutoff and oxbow lake
Figure 5.11
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Running water Drainage patterns
Networks of streams that form distinctive patterns Types of drainage patterns Dendritic Radial Rectangular Trellis
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Drainage patterns Figure 5.22
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Running water Floods and flood control
Floods are the most common geologic hazard Causes of floods Weather Human interference with the stream system
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Running water Floods and flood control Engineering efforts
Artificial levees Flood-control dams Channelization Nonstructural approach through sound floodplain management
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Satellite view of the Missouri River flowing into the Mississippi River near St. Louis
Figure 5.23 top
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Same satellite view during flooding in 1993
Figure 5.23 bottom
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Water beneath the surface (groundwater)
Largest freshwater reservoir for humans Geological roles As an erosional agent, dissolving by groundwater produces Sinkholes Caverns An equalizer of streamflow
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Water beneath the surface (groundwater)
Distribution and movement of groundwater Distribution of groundwater Belt of soil moisture Zone of aeration Unsaturated zone Pore spaces in the material are filled mainly with air
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Water beneath the surface (groundwater)
Distribution and movement of groundwater Distribution of groundwater 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
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Features associated with subsurface water
Figure 5.26
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Water beneath the surface (groundwater)
Distribution and movement of groundwater Distribution of groundwater Porosity Percentage of pore spaces Determines storage of groundwater Permeability Ability to transmit water through connected pore spaces Aquitard – an impermeable layer of material Aquifer – a permeable layer of material
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Water beneath the surface (groundwater)
Features associated with groundwater Springs Hot springs Water is 6–9°C 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
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Old Faithful geyser in Yellowstone National Park
Figure 5.29
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Water beneath the surface (groundwater)
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
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Formation of a cone of depression in the water table
Figure 5.31
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Artesian systems Figure 5.32
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Water beneath the surface (groundwater)
Environmental problems associated with groundwater Treating it as a nonrenewable resource Land subsidence caused by its withdrawal Contamination
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Water beneath the surface (groundwater)
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
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Water beneath the surface (groundwater)
Geologic work of groundwater Caverns 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)
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Cave Features in Lehman Caves, Great Basin National Park, and Carlsbad Caverns National Park
Figure 5.38
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Water beneath the surface (groundwater)
Geologic work of groundwater 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
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Features of karst topography
Figure 5.39 C
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End of Chapter 5
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