1. Landscapes Fashioned by Water Chapter 3

2. Earth’s external processes
Weathering, mass wasting, and erosion are all called external processes
Occur at or near the Earth’s surface
Powered by energy from the Sun
Weathering- the physical breakdown and chemical alteration of rock
Mass wasting- the transfer of rock and soil downslope by gravity
Erosion- the physical removal of material by water, waves, wind, or ice

3. Earth’s internal processes
Mountain building and volcanic activity are internal processes
Derive their energy from Earth’s interior
Erosion, mass wasting, and weathering breakdown rocks, while mountain building and volcanic activity add rocks
RECYCLING!

4. Mass wasting is the downslope movement of rock and soil due to gravity
Causes loss of life and property (USGS- 25 to 50 people killed annually in the U.S.)
Natural disasters
Different from erosional processes - does not require a transporting medium (H2O, wind, glaciers, etc.)
Follows after weathering in the evolution of landforms

6. First the rocks weather….
Then they get mass wasted…..
Then carried out by the river

7. Types of mass-wasting
Debris Flow

8. Slope change through time
Most rapid and spectacular mass-wasting events occur in areas of rugged, geologically young mountains
As mountain building subsides, erosion and mass wasting take over to subdue the terrain

10. Gravity is the controlling force of mass wasting and does not require a trigger to start, but sometimes it does
Examples of triggers
Water
Oversteepening of slope
Removal of vegetation
Earthquakes

11. Water
Heavy rains or snow melt
Pores in sediment become filled, cohesion is lost
Added weight

12. Oversteepened Slopes
A stream under cutting a valley wall, or waves pounding against the base of a cliff
Angle of repose (25 to 40 degrees), steepest angle at which unconsolidated sediments will remain stable

13. Removal of vegetation
Plant root systems bind soil and regolith (weathered rock debris)
If slopes are steep, have rainfall, and remove vegetation….get mass wasting

14. Earthquakes
Most dramatic mass wasting trigger
Dislodge enormous volumes of rocks and unconsolidated material
Liquefication- unconsolidated, saturated sediments are turned into a “liquid”

15. Salmon Beach landslide area, near Tacoma, Washington, after the 2001 Nisqually earthquake. Puget Sound is in the fore-ground

16. Water Cycle The Earth’s hydrosphere
Water content is about 1.36 billion km3 (326 million miles3)
97% in oceans, 2% ice and glaciers, and 1% in lakes, streams, groundwater, and atmosphere

17. Processes in the water cycle
The hydrologic cycle is a summary of the circulation of Earth’s water supply
Worldwide system
Powered by the Sun
Atmosphere is the link between oceans and continents
Processes in the water cycle
Precipitation
Infiltration- H2O soaks into the ground
Runoff- H2O oversaturation does not allow infiltration
Evaporation
Transpiration

18. The water cycle is balanced
Total amount of H2O vapor in the atmosphere remains the same
Average annual precipitation worldwide must be equal to the quantity of water evaporated
Evaporation over the continents is exceeded by precipitation
Precipitation over the oceans is exceeded by evaporation

20. Running water Surface Water
If water is not infiltrated, it becomes runoff. The amount of runoff depends on
Intensity and duration of rainfall
Amount of water already in the soil
Nature of the soil or material
Slope of the land
Extent of vegetation
Is runoff high or low in urban areas?

21. Streamflow
The ability of a stream to erode and transport materials is determined by velocity
Factors that determine velocity
Gradient, or slope
Channel characteristics including shape, size, and roughness
Discharge—The volume of water moving past a given point in a certain amount of time

22. Changes from upstream to downstream
Changes along a stream
Cross-sectional view of a stream is called the profile
Viewed from the head (headwaters or source) to the mouth of a stream
Changes from upstream to downstream
Profile
Profile is a smooth curve
Gradient decreases downstream
Factors that increase downstream
Velocity
Discharge
Channel size

23. Longitudinal profile of California’s Kings River

24. Base Level Base level and stream erosion
Base level is the lowest point to which a stream can erode
Two general types of base level
Ultimate (sea level)
Local or temporary
Changing conditions causes readjustment of stream activities
Raising base level causes deposition
Lowering base level causes erosion

25. Adjustment of base level to changing conditions

26. The work of streams Stream erosion
Lifting loosely consolidated particles by
Abrasion
Dissolution
Stronger currents lift particles more effectively

27. Transport of sediment by streams
Transported material is called the stream’s load
Types of load
Dissolved load
Suspended load
Bed load
Capacity—the maximum load a stream can transport
Competence
Indicates the maximum particle size a stream can transport
Determined by the stream’s velocity

28. Deposition of sediment by a stream
Caused by a decrease in velocity
Competence is reduced
Sediment begins to drop out
Stream sediments
Generally well sorted
Stream sediments are known as alluvium

29. Deposition of sediment by a stream
Delta—Body of sediment where a stream enters a lake or the ocean
Results from a sudden decrease in velocity
Natural levees—Form parallel to the stream channel by successive floods over many years
Floodplain deposits
Back swamps
Yazoo tributaries

30. Structure of a simple delta

31. Natural levees

32. Stream valleys The most common landforms on Earth’s surface
Two general types of stream valleys
Narrow valleys
V-shaped
Downcutting toward base level
Features often include rapids and waterfalls

34. Two general types of stream valleys
Wide valleys
Stream is near base level
Downward erosion is less dominant
Stream energy is directed from side to side forming a floodplain

36. Features of wide valleys often include
Floodplains
Depositional floodplains
Meanders
Cut banks and point bars
Cutoffs and oxbow lakes

38. Drainage basins and patterns
Drainage networks
Land area that contributes water to the stream is the drainage basin
Imaginary line separating one basin from another is called a divide

40. Drainage pattern
Pattern of the interconnected network of streams in an area
Common drainage patterns
Dendritic
Radial
Rectangular
Trellis

42. Floods and flood control
Floods are the most common and most destructive geologic hazard
Causes of flooding
Result from naturally occurring and human-induced factors
Causes include heavy rains, rapid snow melt, dam failure, topography, and surface conditions

43. 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 stream flow

45. 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
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

46. Features associated with subsurface water

47. Movement of groundwater
Porosity
Percentage of pore spaces
Determines how much groundwater can be stored
Permeability
Ability to transmit water through connected pores
Aquitard — An impermeable layer of material
Aquifer — A permeable layer of material

48. Springs Hot springs Geysers
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

49. Video 1
Video 2

50. 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
Artesian wells act as “natural pipelines” moving water from remote areas of recharge great distances to the points of discharge

51. Formation of a cone of depression

52. An artesian well resulting from an inclined aquifer

53. Environmental problems associated with groundwater
Treating it as a nonrenewable resource
Land subsidence caused by its withdrawal
Sinkholes
Contamination

54. 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
Features found with caverns
Form in the zone of aeration
Composed of dripstone
Common features include stalactites (hanging from the ceiling) and stalagmites (growing upward from the floor)

55. Carlsbad Caverns National Park

56. Karst topography
Formed by dissolving rock at, or near, Earth’s surface
Common features
Sinkholes – surface depressions
Sinkholes form by dissolving bedrock and caver collapse
Caves and caverns
Area lacks good surface drainage

57. Features of karst topography