Prepared by Iggy Isiorho for

1
Chapter 5

• Prepared by Iggy Isiorho for
• Dr. Isiorho
• Weathering and Soil
• Index ?

2
On pg. 103

• ? ?

3
Weathering

• Weathering The group of processes that change
  rock at or near the earths surface.
• Erosion The physical removal of rock by an
  agent such as running water, glacial ice, or
  wind.
• Transportation The movement of eroded particles
  by agent such as rivers, waves, glaciers,or wind.
• ? ?

4
Different Weathering

• Mechanical The physical disintegration of rock
  into smaller pieces.
• Fig. 5.1
• Chemical The decomposition of rock resulting
  from exposure to water and atmospheric gases.
• Fig. 5.2
• ? ?

5
Effects of Weathering

• We tend to think of weathering as destructive
  because it mars statues and building fronts. As
  rock is destroyed, however, valuable products can
  be created. Soil is produced by rock weathering,
  so most plants depend on weathering for the soil
  they need in order to grow. Weathering products
  dissolved in the sea make seawater salty and
  serve as nutrients for many marine organisms.
  Some metallic ores, such as those of copper and
  aluminum, are concentrated into economic deposits
  by chemical weathering.
• Differential weathering Varying rates of
  weathering resulting from some rocks in an
  area being more resistant to weathering than
  others. (Fig. 5.5)
• ? ?

6
Mechanical Weathering

• Frost Action
• Abrasion
• Pressure Release
• ? ?

7
Frost Action

• Frost Action Mechanical weathering of rock by
  freezing water.
• Frost Wedging A type of frost action in which
  the expansion of freezing water pries
  a rock apart.
• Fig. 5.6 Fig. 5.7
• Frost Heaving The lifting of rock or soil by
  the expansion of freezing water.
• Back

8
Fig. 5.6

• Back

9
Fig. 5.7

• Back

10
Abrasion

• Another process that can mechanically weather
  rock is abrasion, the grinding away of rock by
  friction and impact during transportation. As
  loose fragments of rock are picked up and moved
  by a stream, they tumble against one another and
  against the rocky stream bottom. (Fig. 5.8)
  Glaciers, waves, and even wind are other agents
  that carry and abrade rock fragments.
• Back

11
Fig. 5.8

• Back

12
Pressure Release

• Pressure Release A significant type of
  mechanical weathering that causes rocks to crack
  when overburden is removed.
• Fig. 5.9
• Sheet Joints Cracks that develop parallel to
  the outer surface of a large mass of expanding
  rock, as pressure is released during unloading.
• Fig. 5.10
• Exfoliation The stripping of concentric rock
  slabs from the outer surface of a rock mass.
• Exfoliation domes A large, rounded landform
  developed in massive rock, such as granite, by
  the process of exfoliation.
• Fig. 5.11
• Back ?

13
Fig. 5.9

• Back

14
Fig. 5.10

• Back

15
Fig. 5.11

• Back

16
Pressure Release II

• Several other processes mechanically weather rock
  but in most environments are less effective than
  frost action, abrasion, and pressure release.
  Plant growth, particularly roots growing in
  cracks (Fig. 5.12A), can break up rocks, as can
  burrowing animals. Such activities help to speed
  up chemical weathering by enlarging passageways
  for water and air. The pressure of salt crystals
  formed as water evaporates inside small spaces in
  rock also helps to disintegrate desert rocks
  (Fig. 5.12B). Extreme changes in temperature, as
  in a forest first, can cause a rock to expand or
  contract until it cracks. Whatever processes of
  mechanical weathering are at work, as rocks
  disintegrate in to smaller fragments the total
  surface area increases (Fig. 5.13), allowing more
  extensive chemical weathering by water and air.
• Back

17
Fig. 5.12

• Back

18
Fig. 5.13

• Back

19
Chemical Weathering

• The processes of chemical weathering, or rock
  decomposition, transform rocks and minerals
  exposed to water and air into new chemical
  products.
• Minerals change gradually at the surface until
  they come into equilibrium, or balance, with the
  surrounding conditions.
• ? ?

20
Soil

• Soil A layer of weathered, unconsolidated
  material on top of bedrock often also
  defined as containing organic matter and
  being capable of supporting plant growth.
• Loam Soil containing approximately equal
  amounts of sand, silt, and clay.
• ? ?

21
Soil Horizons

• Soil horizon Any of the layers of soil that are
  distinguishable by characteristic physical
  or chemical properties.
• O horizon Dark-colored soil layer that is rich
  in organic material and forms just below
  surface vegetation.
• A horizon The top layer of soil, characterized
  by the downward movement of water also called
  zone of leaching.
• B horizon A soil layer characterized by the
  accumulation of material leached downward
  from the A horizon above also called zone of
  accumulation.
• C horizon A soil layer composed of incompletely
  weathered parent material.
• Fig. 5.21
• ? ?

22
Residual and Transported

• Residual soil Soil that develops directly from
  weathering of the rock below.
• Transported soils Soil not formed from the
  local rock but from parent material brought
  in from some other region and deposited,
  usually by running water, wind, or glacial
  ice.
• ? ?

23
Organic Activity

• Organisms contribute to soil development. Plant
  roots break up rocks and burrowing organisms such
  as ants, worms, and rodents bring soil particles
  to the surface and created passageways for water
  and air to get underground, thus speeding up
  chemical weathering.
• Once soil begins to develop on a newly exposed
  rock, it attracts plants and soil organisms that
  increase chemical weathering, accelerating the
  rate of soil development. Partially decayed
  organic matter provides plant nutrients,
  increasing soil fertility.
• ? ?

24
Soils and Climate

• Pedalfer A soil characterized by the downward
  movement of water through it,
  downward leaching, and abundant
  humus. Found in humid climates. (Fig. 5.23)
• Pedocals A soil characterized by little
  leaching, scant humus, the upward movement of
  water through it, and the precipitation of
  salts. Found in dry climates. (Fig. 5.24)
• Laterite Highly leached soil that forms in
  regions of tropical climate with high
  temperatures and very abundant rainfall. (Fig.
  5.25)
• ? Index

25
Fig. 5.1

• Back

26
Fig. 5.2

• Back

27
Fig. 5.5

• Back

28
Fig. 5.21

• Back

29
Fig. 5.23

• Back

30
Fig. 5.24

• Back

31
Fig. 5.25

• Back