Download Weathering & Erosion

Weathering
What Will We Learn In This Chapter?
Distinigiush between weathering and erosion
 Identify variables that affect the rate of weathering
 Analyze the impact of living and nonliving things on the
processes of weathering and erosion.
 Describe the realtionship of gravity to all agents of erosion
 Describe how soil forms
 Explain the relationship between the organic and inorganic
components of soil
 Identify Soil Characteristics
 Recognize soil horizons in a soil profile

Development of Soil
 Almost found every where on earth
 Soil
loose covering of broken rock particles
Plus Decaying Organic Material
Results from
– Chemical Weathering
– Mechanical Weathering
– Biological Activity
Development of Soil
Soil Composition
 Soil is developed from the breakdown of the
exposed bedrock
 As pieces weather they rest on top of bedrock
 Over time soil becomes more inhabitable
 Living and Dead material plus weathered rock
remain
 Residual Soil
Soil located above the parent material
Soil Composition
Soil that is exposed to the elements can be transported.
 This type of soil is called Transported Soil

Check for Understanding

Soil is composed of which of the following?
a)
b)
c)
d)
e)
f)
Weathered rock
Living organisms
Dead organisms
Moisture
Atmospheric gases
All of the above
Check for Understanding

Soil is composed of which of the following?
a)
b)
c)
d)
e)
f)
Weathered rock
Living organisms
Dead organisms
Moisture
Atmospheric gases
All of the above
Soil Profiles
 Soil Profile
Is a vertical sequence of soil layers
 Soil Layers are called…
 Soil Horizons
A distinct layer or zone
4 Types
– O, A, B, C
Classification of an Soil Profile

O Horizon
Living, Organic matter
Grey to Black

A Horizon
Rich in Humus

B Horizon
Enriched with clay

C Horizon
Weathered Parent Material
Soil Profile of Wisconsin
Soil Profiles are Due to Topography
 The topography of a region affects the thickness
of soil
Sloped Areas: thinner layers of soil because of
erosion
Lowlands/Valleys: thicker layers of soil because of
increased deposition
South-Facing Areas: areas facing the south receive
more sunlight  more vegetation  more soil than
areas facing other directions
Soil Types
Classified mainly based of climatic conditions of the area
 4 major types

Polar Soils: very thin layers of soil covering the frozen,
permafrost, ground
Temperate Soils: vary greatly; support vast array of organisms
– Type of soil most of WI has
Desert Soil: receives little precipitation  little vegetation  thin
A soil horizon
Tropical Soil: high temps & precipitation  intense weathering
with a high degree of bacteria in soil  very little humus & few
nutrients found in soil  poor growing soil
Soil Texture

Soil Triangle
Tells us the texture of soil
based on it feel
Three main types of
sediments thatmake up
soil
– Sand
– Silt
– Clay
The proportion of these
sediments give soil its
texture
Weathering is the process that produces
change in the surface of rocks exposed to
the atmosphere and/or hydrosphere.
Two Types OF Weathering:

Mechanical weathering
 Chemical weathering
is breaking rock by force.
is where the rock
material is changed
ex: hitting, scratching,
cracking
into another
substance by reacting
with a chemical.
Frost Wedging


Frost action
(ice wedging)-
1. Water seeps into small
cracks in rocks.
2. When the water freezes it
expands creating great
pressure.
3. The crack widens and
allows water to seep
deeper into the rock.
Root Wedging

Plant action-
1. Tiny root hairs seek
out small cracks and
pits in rock.
2. Once the root hairs
find a place they grow
and expand.
3.The expansion causes
great pressure and
cracks the rock.
Exfoliation
1.
2.
3.
Rocks formed deep in the
Earth are made under high
pressure.
When the pressure is
released the rocks expand
& crack.
May also be caused by
alternate heating and
cooling of rocks by
weather conditions.
Types of Chemical Weathering

OxidationOxygen in the
atmosphere
chemically reacts with
minerals.
ex.: rusting of a nail
Iron Silicates
Iron Sulfides
Types of Chemical Weathering

Hydrolysis
Minerals are dissolved
in water.
ex.: Halite, calcite
Feldspars react with
water to form clay plus
other minerals
Rates of weathering will be influenced by:
Surface area exposed - weathering occurs
on the surface. More surface exposed, the
faster the weathering will occur.
A full, solid block has
the least surface area.
The interior is safe
from exposure.
A smashed piece has
greatest
surface area exposed.
The interior can now be
attacked.
Rates of Weathering will depend on:
 Mineral composition- some minerals are
more resistant than others.
– ex.:Quartz is resistant to chemical and physical
weathering.
Where is the rock more resistant to
weathering?
Where is the rock least resistant to
weathering?
You might also see it like this…
Rates of Weathering will depend on:
 Climatic Conditions:
Cold and/or dry climates favor physical
weathering.
Warm and wet climates favor chemical
weathering.
Frost action works best in areas where the
temperature fluctuates wildly.