1. Geology: Processes, Hazards, and Soils
G. Tyler Miller’s
Living in the Environment
13th Edition
Chapter 10
Dr. Richard Clements
Chattanooga State Technical Community College
Modified by Charlotte Kirkpatrick

2. Key Concepts Internal geologic processes External geologic processes
Minerals, rocks, and the rock cycle
Earthquakes and volcanoes
Soil structure and formation
Soil conservation

3. How do we know?
Most of the evidence for the structure of the earth’s interior come from indirect evidence:
1. density measurements
2. seismic wave studies
3. measurements of heat flow from the interior
4. lava analyses
5. research on metorites

4. Geologic Processes Structure of the Earth
Core: innermost zone, very hot. Has an inner core that is solid and an outer core that is molten
Mantle: thick, solid zone for the most part. Rigid outermost part called Lithosphere has beneath it the very hot melted rock of the Asthenosphere.
Crust: outer part of the earth composed of Continental Crust (Granite) and Oceanic Crust (Basalt)

5. Geologic Processes
Fig p. 204

6. Features of the Crust
Fig p. 205

7. Internal and External Earth Processes
Internal Geologic Processes: generally build up the planet’s surface. Heat from the interior provides the energy plus gravity plays a role as well.
Two types of movement in the mantle’s asthenosphere:
Convection Cells: movement of mantle rock in a convection current
Mantle Plumes: movement of mantle rock in an upward column

8. Convection Cells and Plate Movement

9. Internal Earth Processes
Plate tectonics: theory explaining the movement of the plates that occur at their boundaries
Divergent boundary: spreading plates, such as at the oceanic ridges

10. Internal Earth Processes
Convergent boundary: where the plates come together
Subduction zone: due to the density difference between oceanic and continental crust the oceanic crust will be carried downward and a trench is formed here. Earthquakes are common as well as volcanoes.

11. Internal Earth Processes
Transform fault: fault line that develops when plate movement is in opposite direction and therefore the plates slide past one another along a fracture.

12. Incidence of Earthquakes and Volcanoes
Ring of Fire

13. Tectonic Plates

14. External Earth Processes: Erosion and Weathering
Refer to Fig p. 209
Erosion: process by which material is dissolved, loosened or worn away from one part of the earth’s surface and deposited in other places.
Mechanical weathering: Large rock mass is broken into smaller fragments of the original material. Ex. Frost wedging
Chemical weathering: one or more chemical reactions decompose a mass of rock usually reaction with O2, CO2, and water.

15. Minerals and Rocks Igneous (granite, lava)
Mineral (diamond, bauxite): element or inorganic compound that occurs naturally and is solid.
Rock Types: Rocks are any material that make up a large, natural, continuous part of the earth’s crust. May contain one or more minerals.
Igneous (granite, lava)
Sedimentary (limestone, sandstone)
Metamorphic (marble, slate)

16. Sedimentary Rock Heat, Pressure Heat, Igneous Rock Metamorphic Rock
Shale, Sandstone,
Limestone
Deposition
Transport
Erosion
Heat,
Pressure
Weathering
External Processes
Internal Processes
Heat,
Pressure
Igneous Rock
Granite, Pumice,
Basalt
Metamorphic Rock
Slate, Quartzite,
Marble
Magma
(Molten Rock)
Refer to
Fig p. 210

17. Natural Hazards: Earthquakes
Features: Energy released as shock waves when the stressed parts of the earth shift.
Focus: point of initial movement.
Epicenter: the point on the surface directly above the focus
Magnitude: severity of the earthquake as measured on a Richter scale. It is measured by a seismograph. The amplitude of the vibrations caused by the energy released by the earth movement is what is measured. Each increase in the scale is 10 times greater in magnitude.

18. Natural Hazards: Earthquakes
Fig p. 210

19. Natural Hazards: Earthquakes
Aftershocks and foreshocks may show up before or after a main shock from minutes to days.
Primary effects: shaking and vertical or horizontal displacement
Secondary effects: rock slides, urban fires, flooding caused by subsidence, and tsunamis.

20. How to reduce earthquake risk
Locating active faults
Making maps of high risk areas
Establishing buildings codes that regulate risk
trying to predict when and where earthquakes will occur.

21. Expected Earthquake Damage
Canada
United States
No damage expected
Minimal damage
Moderate damage
Severe damage
Fig p. 211

22. Volcanoes Occur in same areas as earthquakes.
Occurs where magma reaches the earth’s surface through a central vent or a long crack
Can release ejecta (chunks of lava rock to ash), liquid lava, or gases (water, carbon dioxide, sulfur dioxide)
Much of the sulfur dioxide will remain in the air and become acid rain
Some are very explosive eruptions like Mt. St. Helens and Mt. Pinatubo; others are much quieter like the Hawaiian Island volcanoes
Benefit: produces very fertile soil

23. Natural Hazards: Volcanic Eruptions
extinct
volcanoes
magma
reservoir
central
vent
conduit
Solid
lithosphere
Upwelling
Partially molten
asthenosphere
Fig p. 211
See Introductory Essay p. 203

24. How to Reduce Volcano Risk
Land use planning
Better prediction of volcanic eruptions
Effective evacuation plans
Studying phenomenon that precedes the eruption
Tilting or swelling of the cone,
Changes in magnetic and thermal properties of the volcano
Changes in gas composition
Increased seismic activity

25. Soils: Formation
Soil: a complex mixture of eroded rock mineral nutrients, decaying organic matter, water, air and billions of living organisms, mostly of the microscopic decomposers.
Soil horizons: mature soil is arranged in a series of zones called soil horizons. Each has a very distinct texture and composition that varies with different types of soils.
Soil profile: cross sectional view of the horizons in a soil. Most mature soils have at least 3 horizons of the possible horizons.

26. Soils: Formation
Soil Horizon O: Surface litter layer, consists mostly of freshly fallen and partially decomposed leaves, twigs, animal waste, fungi and other organic materials.
Soil horizon A: Topsoil layer, a porous mixture of partially decomposed organic matter called humus, some inorganic mineral particles. Usually darker and looser than deeper layers. A fertile soil will have a thick topsoil with lots of humus.
B and C horizons: inorganic matter and broken-down rock

27. Fig. 10-12 p. 212 Regolith Bedrock Immature soil Leaf litter Topsoil
O horizon
Leaf litter
A horizon
Topsoil
B horizon
Subsoil
C horizon
Parent
material
Mature soil
Young soil
Regolith
Bedrock
Immature soil
Fig p. 212

28. Food Web of Soil

29. Importance of Nitrogen Cycle

30. Soil Profiles for Different Biomes

31. Soil Profiles for Different Biomes

32. Soil Properties
Infiltration: When water percolates downward through the soil through the pores.
Leaching: During the percolation the water dissolves various soil components in the upper layers and carries them to the lower layers.

33. Soil Properties
Texture: the relative amounts and types of mineral particles. (clay, silt, sand, and gravel)
Loams: are a roughly equal mixture of all the above.
Structure: ways soil particles are organized and clumped together.

34. Increasing percentage sand
100%clay
Increasing
percentage silt
percentage clay 20 40 60 80
100%sand
100%silt
Increasing percentage sand
Fig
p. 216

35. Soil Properties
Porosity: determined by soil texture, it measures the volume of pores or spaces per volume of soil and the average distances between those spaces.
Permeability: the rate at which water an d air move from upper to lower soil layers. Influenced by the average size of the pores and the soil structure.
pH: Measures alkalinity or acidity of soil and influences the uptake of nutrients by plants. To correct soil that is too acidic, add lime. When too alkaline add sulfur.

36. Water
High permeability
Low permeability
Fig p. 217

37. Table 10-1 p. 216
Texture Nutrient Infiltration Water-Holding Aeration Tilth
Capacity Capacity
Clay Good Poor Good Poor Poor
Silt Medium Medium Medium Medium Medium
Sand Poor Good Poor Good Good
Loam Medium Medium Medium Medium Medium
Refer to Fig p. 215

38. Soils: Erosion
Sheet erosion: occurs when water moves down a slope or across a field in a wide flow and peels off fairly uniform sheets or layers of soil.
Rill erosion: occurs when surface water forms fast-flowing rivulets that cut small channels in the soil.
Gully erosion: when rivulets of fast-flowing water join together and with each succeeding rain cut the channels wider.
See Fig p. 217

39. Harmful effects of Soil Erosion
Loss of soil fertility and its ability to hold water
Runoff of sediment that pollutes water, kills fish and shellfish, clogs irrigation ditches, boat channels, reservoirs, and lakes.
Soil is a renewable resource because natural processes regenerate it; however, we use it or degrade it faster than it naturally regenerates (in tropical soil it may take 200-1,000 years) therefore making it a nonrenewable resource.

40. How Serious Is the Problem of Soil Erosion?
Causes loss of soil organic matter and vital plant nutrients
Reduced ability to store water for use by crops
Increased use of costly fertilizer to maintain soil fertility
Increased water runoff on eroded mountain slopes that can flood agricultural land and dwellings in the valleys below
Increased buildup of soil sediment in waterways and coastal areas that reduce fish production and harms other aquatic life
Increased input of sediment into reservoirs

41. Areas of serious concern Stable or nonvegetative areas
Global Soil Erosion
Areas of serious concern
Areas of some concern
Stable or nonvegetative areas
Fig p. 218

42. Dust Bowl

43. Soil Erosion in the U.S.
Erosion in the U.S. has been a major concern for years as the farmers plowed over the fields every year at harvest and left it bare for a long period of time allowing it to be eroded mainly by wind.
Since the great Dust Bowl of the 1930’s, caused by a severe drought and over-plowing for years, the development of the Soil Conservation Service ahs made the prevention of soil erosion their top priority. (now known as the National Resources Conservation Service) See page 219.

44. Desertification: the productive potential of arid and semiarid land falls below 10% or more due to a combination of factors.

45. Salinization: Excess buildup of salts from over irrigation
Salinization: Excess buildup of salts from over irrigation. Causes stunted plant growth, lower crop yields, and eventually kill the plant an druins the land.

46. Waterlogging: Large amounts of irrigation water are used to leach salts deeper into the soil. However many times the soil doesn’t have good drainage and there is an accumulation of water as the water table rises. The roots get enveloped in water and lower their productivity and killing them after prolonged exposure.
Evaporation
Transpiration
Waterlogging
Less permeable
clay layer
Fig p. 221

47. Solutions: Soil Conservation
Soil Conservation: reducing soil erosion and restoring soil fertility. Most often done by keeping the soil covered.
Conventional-tillage: Soil is plowed in the fall and left bare through winter and early spring and vulnerable to erosion
Conservation tillage: disturb soil as little as possible while planting crops.
Minimum tillage and no-till farming allow for the land to remain with crops residues and cover vegetation without disturbing the topsoil.

48. Solutions: Soil Conservation
Cropping methods: various cropping methods are used to reduce erosion, largely by working with the land and protecting the removal of topsoil. Include: terracing, contour planting, strip cropping, alley cropping, windbreaks, and gully reclamation.
Land Classification: classify the land to identify whether it is suitable for cultivation.

49. Advantages and Disadvantages of Conservation Tillage

50. Additional Soil Conservation Cropping Methods

51. Soil Restoration Organic fertilizer: plant and animal waste
Animal manure: from cow, goat ,chicken, horses, etc.
Green manure: from plant wastes
Compost: sweet dark brown humus like material rich in organic matter.
Spores: spores that attach to roots to help absorb nutrients
Crop rotation: rotate crops that deplete soil with those that conserve and add nutrients to the soil

52. Commercial inorganic fertilizer : contain nitrogen, phosphorous and potassium. They may contain trace amounts of other required nutrients.
Easily transported, stored and applied. Used extensively worldwide.
Problems:
They don’t add humus to the soil
Reduce soil organic matter and ability to hold water
Lowers oxygen content and ability to take up nutrients
Not all nutrients needed are included
Lots of energy needed for production, transport and application
Increase global warming by release of N2O