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ES 8 WEATHERING AND SOIL FORMATION:
Weathering is the breakdown of rocks into smaller pieces
called sediment.
Two types of weathering:
1. Mechanical— physical breakdown of a rock
into smaller fragments, each
with the same properties as the
original.
WHAT CAUSES MECHANICAL
WEATHERING
1. Ice wedging: water squeezes into
cracks in rocks and expands making
the crack wider and thus wedging the
rock apart.
2. Wind: nature’s method of sand
blasting.
3. Water: has abrasive
powers. Abrasion is where
rocks rub against each
other in a grinding action.
This occurs mostly in
streams and rivers where
fragments bounce off each
other and become rounded.
Rounded Rocks Used to
be Underwater
4. Plants/animals: roots
can penetrate cracks and
physically pry rocks apart
as the root grows in size.
Animals burrowing in soil
expose fresh surfaces that
will continue weathering.
Root Wedging
2nd Type of Weathering
2. Chemical—chemical reactions dissolve minerals in
rocks or change them into different minerals or into a
new substance. Look for words like dissolved,
rusting, mixing, oxidation and decaying
RUSTING
DECAYING
HOW FAST DOES WEATHERING HAPPEN?
It depends on several things:
1. Different rock types weather at different rates
2. The environment: cold, warm, wet, dry, humid, etc.
WHAT HAPPENS WHEN ROCKS ARE COMPLETELY
BROKEN DOWN?
•You have soil!!!
•Soil is a mixture of pieces of broken down rocks and
organic materials
When soil forms, it ends up in a series of layers called
horizons.
This monument in Egypt has weathered little in 3000 years. The
same kind of monument in New York City has weathered
significantly in only 100 years.
Soil profiles are when the
soil is looked at in cross
sections. When looking at
soil profiles, you can tell
the difference between
mature soil formation and
immature soil formation.
Mature soils have had
enough time to develop
distinct horizons. Immature
soils do not have distinct
horizons.
A Immature
MATURE SOIL
An
SoilPROFILE
Profile
…no horizons
Horizon Profile:
“A” horizon—top soil layer
Also called topsoil
Is very dark in color
Contains the most humus (organic soil where plants
grow) and less rock particles
“B” horizon—middle soil layer
Also called subsoil
Much lighter than A
Contains less humus than A
Minerals travel from A to B
horizon in a process called
leaching
“C” horizon — bottom soil layer
•Contains weathered or broken rock—the parent
material of the soil
•Has very little organic matter
“D” horizon — bedrock which is solid rock…no dirt
AMAZING EARTH SCIENCE FACTS
Weathering
•__________________
is the process that rocks are broken
down by water, air and organisms.
Mechanical
•___________________
weathering occurs in cold climatesice wedging
warm,humid climates
•Chemical weathering occurs in ________________
•Soil evolution starts with the weathering of _____________
bedrock
Organic material must be present in order to have soil
•___________
•Soil profile consists of 3 horizons
Top soil
A-_______________
(most evolved)
leaching from A
B-Less humus, ____________
Weathered rock
C-______________
D- Known as solid rock or _______________
bedrock
aaaaaaaaaaaaaaaa
…and this glorious cliff-top
property has recently been
reduced by 50%