Download Development of Soil-Student Info

DEVELOPMENT
OF SOIL
What are the 5 Factors which aid in soil
formation?
1.
2.
3.
4.
5.
5 Factors which aid in soil formation?
1. Parent Material (unconsolidated
bedrock)
2. Climate
3. Living organisms
4. Landscape position
5. Time (300 to 1000 years to
form!!!!)
Weathering by Temperature Extremes
Plant Roots Effects on Rocks
Lichens are
common
primary
colonisers of
surfaces
They cause
chemical
weathering,
releasing small
quantities of
organic acids
which can
dissolve
limestone
Foliose lichen
Wind Effects on Rocks
Water Effects on Rocks
Ice Effects on Rocks
Man Made Effects on Rocks
What are the stages of Soil
Development?
Stages of Soil Development
 Weathering of rock produces soil.
 Through time - vegetation grows on the land surface
 Rainwater moves through the soil, carrying
weathering products from the surface to lower
depths
 Forming soil horizons
 Organic matter accumulates at the surface when
vegetation dies forming topsoil (A horizon)
 Then, mineral subsoil begins to oxidize (C horizon)
 Water translocates weathering products of clay, iron
oxides, and caliche into a layer called B horizon
 With time, soils get thicker, gain horizons, and
become clay-rich and redder.
What is the difference between soil
formation and weathering?
What is the difference between soil
formation and weathering?
 All soils initially come from rocks, ‘parent material’.
 The Parent Material may be directly below the soil, or great
distances away (wind, water or glaciers have transported the
soil)
 The soil formation process is termed 'pedogenesis'.
 Climatic conditions are important factors affecting both the
form and rate of physical and chemical weathering of the
parent material.
 Soil formation is a combination of the products:
 Of weathering
 of structural development of the soil,
 of differentiation of that structure into horizons or layers,
 and lastly of its movement or translocation
 In fact there are many ways in which soil may be transported
away from the location where it was first formed.
Weathering?

Weathering
 Breakdown of rock to form sediment
 Types of Weathering?
 Physical or mechanical weathering (Biological weathering)
 & chemical
 http://facstaff.gpc.edu/~pgore/geology/geo1
01/weather.htm
5 Factors in Weathering of Minerals
1. _____________ alterations that crack
rock
2. _______________that pry cracks in
rocks open
3. _____________ grinding of wind,
water, and ice
4. ____________producing organic
acids that chemical react with rocks
to further weaken it.
5. ___________weathering occurs over
eons of geological time
5 Factors in Weathering of Minerals
Temperature alterations that crack
rock
Plant roots that pry cracks in rocks
open
Abrasive grinding of wind, water,
and ice
Lichens and microbes producing
organic acids that chemical react
with rocks to further weaken it.
Time weathering occurs over eons of
geological time
Weathering
All materials are susceptible to weathering.
Weathering is a natural process.
Mechanical weathering is the physical breaking
up of rocks. (ie. plant roots, freeze & thaw, shifting of the earth’s
surface)
Chemical weathering is the actual altering of
rock, changing it into a different substance.
(Water combines with carbon dioxide to create
carbonic acid)
Erosional agents – wind, water, and glaciersalso disintegrate rock particles even further.
What is the difference between
Mechanical & Chemical Weathering?

Mechanical or Physical Weathering
 Freezing and Thawing - can literally grind mountains
down over time!
 Heating and Cooling - expand and contract. The effect
is less pronounced that that of freezing and thawing but
over time this can become significant.
 Wetting and Drying - soils that swell and shrink. Clay
minerals in particular exhibit this property.
 Grinding or Rubbing - most obvious on the beach,
grinding of particles against each other leads to particle
disintegration. This is why beach pebbles become
smooth. Abrasion similarly breaks down the soil particles.
Mechanical or Physical Weathering
 Organisms - Soil is home for a wide range of organisms. If
plants can push through concrete - soil presents little
obstacle! Worms churn their way through soil, mixing
and aerating it all through their lives and there can be
thousands of worms in a field.
 Unloading - when pressure is placed upon soil it
becomes compressed. Never mind tractors, imagine the
weight of a glacier! When ice melts a huge weight is
lifted and the soils may react accordingly by uplifting
and expanding.
What are 3 examples of natural erosional
agents? –
This was stated in mechanical weathering
Water is the main chemical weathering
agent
Oxygen dissolved in water will oxidize with
certain materials.
Also, as rain falls through the atmosphere it
dissolves some carbon dioxide to from carbonic
acid.
The result is that water everywhere on Earth’s
surface is slightly acidic and this acid destroys
certain minerals’ crystalline structure.
Clay minerals are generally the end product of
chemically weathering.
Define Erosion
Erosion
 The wearing away and transportation of the earth’s weathered surface
What are the 4 natural forces that may
cause erosion?
1.
2.
3.
4.
Erosion
1.
Wind
2.
Water
3.
Glacial action
4.
Gravity (from a point of high elevation to a lower elevation)
Explain the 5 different types of
parent material based on how they were
transported?
1.
2.
3.
4.
5.
How did the soils get there?
Types of parent material?
1. Sedentary –
soils that weather from bedrock and
remain in place
Bedrock –
 solid unweathered rock lying beneath surface
deposits of soil
2. Colluvial –
soils that have moved in response to
gravity
3. Alluvial –
Soils that are carried in water such
as rivers. These are deposited on
flood plains and at deltas
4. Aeolian –
Soils that are transported and
deposited by winds
5. Glacial till –
Soils deposited by glaciers
How wind erodes the soil?
Define the following forms of wind erosion -
Saltation –
How wind erodes the soil???
Saltation –
Fine and medium sand-sized
particles move mainly by
saltation “bouncing particles”.
50-80% of the total soil is moved
this way
Most soil movement is within a
foot of the ground
How wind erodes the soil?
Suspension –
Suspension –
Very fine soil particles are lifted
from the surface by the impact of
saltation
This “dust” is carried high into the
air for long distances
Small % of the total soil moved by
wind is this way
These particles are the most fertile
part of the eroded soils
How wind erodes the soil?
Surface creep –

Surface creep –
The movement of larger (sandsized) soil particles along the
surface of the soil.
Loosened by saltation particles
Too large to be lifted off the
ground in most winds
Rolling motion along the surface
25% of the soil is moved this way
What are the 5 Major types of erosion by
water and explain each type?
1.
2.
3.
4.
5.
Soil Erosion
by
Water
Water causes about 2/3 of the erosion on
our land. Soil is the largest pollutant in our
waterways
Our soil erosion problems
began in colonial
times….
“When our fore-fathers settled
here…the Land being new they
depended upon the Natural Fertility of
the Ground…and when they had worn
out one piece they cleared another…”
- Jared Eliot, Ct. minister, doctor, and farmer, 1748
A Natural Stream
A Damaged Stream
Long-term accumulations of sediment,
nutrients, and pesticides have
damaged vital aquatic resources..
Major types of erosion by water:
SPLASH EROSION –
Soil particles loosened by water
drops
SHEET EROSION –
Surface carrying soil particles
detached by water drops
RILL EROSION –
Small eroding channels or water
paths
GULLY EROSION –
Large volumes of soil removed by
scouring the sidewalls. Creating
verticle walls
MASS EROSION OR SLUMPING –
Large areas of soil slide or creep
downhill. Potential for gully
erosion
What are the best
agricultural soils?
What are the best
agricultural soils?
They are loam
Most alluvial and glacial till soil is best
Colluvial soils are coarse textured and
contain undesirable chemical and
physical qualities
Aeolian soils are finely textured and
vary
greatly in their productivity
Sedentary soils may be useful for
agriculture if they have not lost
their nutrient elements
How do sedentary soils loose their
nutrients?