GEOLOGY 101 Weathering, Erosion, and Soil Related to Chapter

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GEOLOGY 101

• Weathering, Erosion, and Soil
• Related to Chapter 6 in Monroe and Wicander

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WEATHERING
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Earth's external processes

• Weathering the disintegration and decomposition
  of material at or near the surface
• Mass wasting the transfer of rock material
  downslope under the influence of gravity
• Erosion the incorporation and transportation of
  material by a mobile agent, usually water, wind,
  or ice

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Weathering

• Two kinds of weathering
• Mechanical weathering
• Breaking of rocks into smaller pieces
• Processes of mechanical weathering
• Frost wedging
• Unloading
• Jointing
• Thermal Expansion
• Biological activity

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Frost wedging
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Unloading and exfoliation of igneous rocks
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Weathering

• Two kinds of weathering
• Chemical weathering
• Alters the internal structures of minerals by
  removing or adding elements
• Most important agent is water
• Oxygen dissolved in water oxidizes materials
• Carbon dioxide (CO2) dissolved in water forms
  carbonic acid and alters the material

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Weathering

• Two kinds of weathering
• Chemical weathering
• Weathering of granite
• Weathering of potassium feldspar produces clay
  minerals, soluble salt (potassium bicarbonate),
  and silica in solution
• Quartz remains substantially unaltered
• Weathering of silicate minerals produces
  insoluble iron oxides and clay minerals

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Rates of weathering

• Advanced mechanical weathering aids chemical
  weathering by increasing the surface area
• Important factors
• Rock characteristics
• Mineral composition and solubility
• Physical features such as joints

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Increase in surface area by mechanical
weathering
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Rates of weathering

• Important factors
• Climate
• Temperature and moisture are the most crucial
  factors
• Chemical weathering is most effective in areas of
  warm temperatures and abundant moisture

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Rates of weathering

• Differential weathering
• Caused by variations in composition
• Creates unusual and spectacular rock formations
  and landforms

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Joint-controlled weathering in igneous rocks
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Soil

• An interface in the Earth system
• Soil is a combination of mineral matter, water,
  and air that portion of the regolith (rock and
  mineral fragments) that supports the growth of
  plants

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Typical components in a soil that yield
good plant growth
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Soil

• Soil texture and structure
• Texture refers to the proportions of different
  particle sizes
• Sand (large size)
• Silt
• Clay (small size)
• Loam (a mixture of all three sizes) is best
  suited for plant life

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Soil Texture
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Soil

• Soil texture and structure
• Structure
• Soil particles clump together to give a soil its
  structure
• Four basic soil structures
• Platy
• Prismatic
• Blocky
• Spheroidal

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Soil

• Controls of soil formation
• Parent material
• Residual soil parent material is the bedrock
• Transported soil parent material has been
  carried from elsewhere and deposited
• Time
• Important in all geologic processes
• Amount of time to evolve varies for different
  soils

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Soil

• Controls of soil formation
• Climate
• Plants and animals
• Organisms influence the soil's physical and
  chemical properties
• Furnish organic matter to soil

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Soil

• Controls of soil formation
• Slope
• Angle
• Steep slopes often have poorly developed soils
• Optimum is a flat-to-undulating upland surface
• Orientation (direction the slope is facing)
  influences
• Soil temperature
• Moisture

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Soil

• Soil Profile
• Soil forming processes operate from the surface
  downward
• Horizons zones or layers of soil
• Horizons in temperate regions
• O organic matter
• A organic and mineral matter
• E little organic matter

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Soil

• Soil Profile
• Horizons in temperate regions
• B zone of accumulation
• C partially altered parent material
• O and A together called topsoil
• O, A, E, and B together called solum, or "true
  soil"

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An idealized soil profile
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A soil profile showing different horizons
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Soil

• Classifying soils
• System for classifying soils in the United States
  is called the Soil Taxonomy
• Emphasizes physical and chemical properties of
  the soil profile
• Names of the soil units are combinations of
  syllables of Latin and Greek origin

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Soil Type and Climate

• Climate is the most important factor in
  determining the type and rate of soil formation.
• In general, warm, moist temperate climates
  develop pedalfer soils. Most of the eastern U.S.
  and much of Canada are composed of this type of
  soil.
• Soils in much of the arid and semiarid western
  U.S. and western Canada are pedocals.
• Laterites are soils that form in the tropical
  climates where chemical weathering is intense and
  leaching of soluable minerals is intense.

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Climate and Soil Formation
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(from http//www.geo.wvu.edu/kammer/g100/Weather
ing.pdf)
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Climate and Soil Formation
Soil
Soil
Where precipitation is high and the temperatures
are warm, soil will be the thickest.
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Activities of Organisms

• Organisms such as bacteria, fungi, algae,
  burrowing animals, earthworms, ants, termites,
  etc. live in the soil and help break mineral
  matter down and mix soil particles. They also
  provide humus when they die. Microorganisms help
  break down plant material that provides nutrients
  and humus to the soil. Organic acids (like
  acetic acid, etc.) produced by decaying organisms
  are important in further chemical weathering of
  rock material.

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Relief and Slope

• Topographic relief is the difference between the
  highest elevation and lowest elevation in an
  area. In areas of high relief, mountainous
  areas, climate changes with elevation this is a
  big factor on rate of soil formation. Obviously
  colder conditions at high elevations slows down
  soil formation processes.
• Slope. Steep slopes have little or no soil
  formation because weathered materials erodes
  faster than soil-forming processes operate.
  Slope direction is also and important factor in
  soil formation. In the northern hemisphere,
  north facing slopes receive less sunlight and are
  thus colder, have different types of vegetation,
  and generally are slower in soil formation.

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END CHAPTER 6