Weathering and Soil Formation

1
Weathering and Soil Formation
2
Weathering

• Weathering the breaking down of rock and other
  materials on the Earths surface. A slow,
  continuous process. The effects are not always
  easily observed and others are obvious. Example
  paint peeling
  off a house.

3
Weathering cont.

• Rocks are broken down by
  two types of weathering.
• Mechanical when the forces of weathering break
  rocks into smaller pieces but do not change the
  chemical makeup of the rocks.
• Chemical the chemical makeup of the rock is
  changed.

4
Mechanical Type 1

• Temperature heat causes the outside of rock to
  expand, cooling causes the rock to contract.
  This continuous cycle causes the rock
  to go through exfoliation (curved sheets
  or slabs).

5
Mechanical Type 2

• Ice Wedging the repeated freezing and melting of
  water that has seeped into the cracks of the
  rocks. Example road ways, drive ways)

6
Mechanical Type 3

• Organic Activity a plant growing in a crack,
  roots of plants loosen rock material or any
  activity caused by living things.

7
Mechanical Type 4

• Gravity pulls loosened rocks off of cliffs or
  mountain sides.
• Example Landslide large movement of loose
  rocks and soil.
• Example Avalanche large movement of loose
  rocks and snow.

8
Landslide Story
9
Mechanical Type 5

• Abrasion wind-blown sand causes weathering of
  rocks. Carried by wind, water, or other forces.
  Causes riverbed rocks to be rounded and smooth.

10
Chemical Type 1

• Water (universal solvent) can dissolve most of
  the minerals that hold rocks together. Can also
  form an acid when mixed with certain gases which
  speeds up decomposition.

11
Chemical Type 2

• Oxidation oxygen chemically combines with
  another substance. The result is an entirely
  different substance. Iron in rocks turns to rust.

12
Chemical Type 3

• Carbonation carbon dioxide dissolves in rain
  water, forming a weak acid called carbonic acid.
  Dissolves certain rocks (feldspar and limestone).
• Acid Precipitation air polluted with sulfur
  oxides (from burning coal) dissolve in rain.
  Causing acid rain to fall which corrodes rocks,
  metals, and other materials quickly.
• Plant Acids produce weak acids that dissolve
  certain minerals in rocks (example mosses and
  lichens)

13
Formation of a Cave
14
Is this weathering your brain?
15
(No Transcript)
16
Differential Weathering

• The composition of rock greatly affects the rate
  at which rock weathers
• Softer rock weathers away leaving the harder more
  resistant rock behind
• Limestone and other sedimentary rocks that
  contain calcite weather rapidly while other
  sedimentary rock weather faster depending on what
  cements them together
• Some are more resistant than igneous

17
Rate of Weathering

• Amount of exposure can determine the rate, the
  amount of rock that is exposed, and the amount of
  time
• More surface area means more weathering
• Fractured and jointed rock weathers faster
• Climate that has extreme seasons allows the
  greatest rate of weathering. Hot dry climates
  allow the least amount of weathering
• Higher elevations and steeper topography allow
  for faster weathering
• Plant, animal, and human activities can
  accelerate weathering.

18
(No Transcript)
19
Soil Formation

• Soil- formed when rocks are continuously broken
  down by weathering and is extremely important for
  most living organisms.\
• Plants - food (minerals/water)
• Animals plants/animals to eat.

20
(No Transcript)
21
Types of Soils

• Residual soil remains on top of its parent rock
  and has similar chemical composition.
• Transported soil moved from its origin by wind,
  water, glaciers, wavesand can be completely
  different than the rock is lays upon
• Humus decayed material (plants/animals).
  Important for the growth of plants because it
  helps to speed up the breakdown of rocks into
  soil. Moles, earthworms, ants, and beetles help
  break down big pieces of soil. Filled with
  nutrients.

22
Soil Composition

• Pieces of weathered rock and organic material
  (humus) are the two main ingredients of soil.
• Rock particles are more than 80 and air and
  water are present in the pore spaces.
• Clay and quartz are the most abundant because
  they are very stable.
• Nitrates (potassium, phosphorous, and nitrogen)
  are vital to plant growth and found in
  fertilizers.
• Why are pore spaces important for plants?

23
Worm Farm
24
Soil Texture

• Type of weathering affects the composition of the
  soil and the texture of the soil (size of
  grains).
• Gravel between 2 and 64 mm in diameter.
• Sand less than 2mm
• Silt 1/16th of a mm
• Clay less than 1/256th of a mm

25
Soil Horizons

• Soil Horizons soil layers.
• Each horizon is different. A cross section is
  called a soil profile.
• Soil that has 3 layers is mature (takes many
  thousands of years and the right conditions.
• Factors surface features, time, climate and
  type
• Soil that has 2 layers is immature.

26
Horizons

• Horizon O-part of the A layer where all the
  organic material is produced.
• Horizon A uppermost layer, dark colored, much
  activity by living occurs, top-soil (humus) most
  fertile.
• Horizon B leached out minerals, clay and some
  humus, called subsoil, formed very slowly.
• Horizon C partly weathered rocks, extends down
  to top of un-weathered parent rock composition
  similar to parent rock.

27
Soil and Climate

• Tropical soils- soils develop quickly, top layer
  called laterites that contain Fe and AL
• Temperate soils- A, B, and C are thick. Areas
  that receive 65 cm of rain have a top layer
  called pedalfur that contains clay, quartz, and
  Fe.
• Areas that receive less rain have a top layer
  called pedocal that contains CaCO3
• Desert and Arctic soils- thin with little humus

28
(No Transcript)
29
Try and Get excited about dirt
30
Soil Erosion

• Weathered material are transported by gravity,
  wind, glaciers, and water

31
Gullying and Sheet Erosion

• Soil that is washed away with each rainfall can
  furrow and eventually become gullies.
• Sheet erosion - when the top layer of soil is
  washed away

32
Soil Conservation

• Contour Strip
  Terracing
• Plowing Cropping

33
A true soil lover!!!!