Soil
Benchmark(s)
• Explain how rocks are broken down,
how soil is formed, and how surface
features change.
Introduction Video
Weathering
• Weathering is the term used to
describe the breaking of rocks into
smaller fragments. There are two types
of weathering
• 1. physical and
• 2. chemical.
Physical Weathering
• Physical weathering is weathering that
breaks apart rocks without changing
their chemical composition. Water,
wind, or gravity are usually responsible
for physical weathering.
Chemical Weathering
• Chemical weathering occurs when
water, air, and other substances react
with the minerals in rocks. An example
of chemical weathering is when the
acids in rainwater dissolve away rocks.
Water is the main cause of chemical
weathering. Chemical weathering is
most rapid in regions with much
moisture and warm temperatures.
• When we look at a landscape, we
usually see grass, plants, and trees.
Without soil these would not exist. Soil
is a complex mixture of fresh and
eroded rocky material, dissolved and
redeposited minerals, and the remains
of once living things.
• These components are mixed together by the
burrowing of animals, the pressure of plant roots,
and the movement of water underground.
• The type of soil, its chemical composition,
and the nature of its organic origin are all
important to agriculture.
• Many different types of soils exist.
• Soils vary depending on the climate.
• Soil is formed in a number of layers.
• Their sequence is called the soil profile.
• The layers, also called horizons, show the
different things that go into making a soilfrom the decay of rocks to the addition of
material from living things.
• Not all soils have the same horizons,
and their sizes vary from soil to soil.
• There are generally five horizons.
Soil Horizons
• Horizon 0 is the humus layer that contains
deposits of plant material. Horizon A is the
topsoil. This is organically rich, but some
minerals are taken out by groundwater.
• Horizon B, the subsoil, is less organic, but is
rich in minerals brought down from the
topsoil.
• Horizon C, the parent rock, is broken and
weathered into loose chunks, and contains
no organic material.
• Horizon D is the underlying bedrock. The
mineral content of the soil comes from this.
Erosion
• Erosion is the process that moves
weathered sediments from one location
to another. The four major agents of
erosion are gravity, running water,
glaciers, and wind.
• Rainwater falls to form pools of water or
sinks into the soil and re-emerges as
springs.
• This water is channeled into valleys and
hollows, eventually forming the streams and
rivers that flow down to the sea.
• Flowing water helps shape the landscape. It
wears away the rocks of the mountains,
again depositing the debris on the plains and
lowlands, and eventually the floor of the sea.
Erosion
• Erosion is the process that moves weathered
sediments from one location to another.
• The four major agents of erosion are gravity,
running water, glaciers, and wind.
• When gravity alone causes material to move,
its called mass movement.
• Some mass movements are very slow; other
types happen very quickly.
• Some different types of mass movements are
slumps, creeps, rockslides, and mudflows
Water Erosion
• Water erodes more sediments than any
other agent of erosion. Water erosion
can be classified into rill erosion, gully
erosion, and sheet erosion. Rill erosion
begins when a small stream forms
during a heavy rain.
Gulley Erosion
Rill Erosion
• If a stream
frequently
flows in the
same path,
rill erosion
may evolve
into a gully
erosion.
Sheet Erosion
• When
rainwater
flows into
lower
elevations
and carries
sediments
with it.
Glaciers
• A moving mass of ice and snow is a glacier.
• A glacier is an accumulation of ice, air, water,
and rock debris or sediment.
• It is a large enough quantity of ice to flow
with gravity due to its own mass.
• Glaciers flow very slowly, from tens of
meters to thousands of meters per year (tens
of feet to thousands of feet per year).
Glaciers
• The ice
can be as
large as a
continent,
such as
the ice
sheet
covering
Antarctica.
Continental Glacier
• There are two
types of
glaciers:
continental
glaciers and
valley glaciers.
Continental
glaciers are
huge masses
of ice and snow
found near
Earth's polar
regions.
Valley Glaciers
• Valley glaciers
are located in
mountainous
areas where the
average
temperature is
low enough that
snow does not
melt over the
summer
season.
Regions in Michigan where erosion
by wind, water, or glaciers have
occurred:
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river valleys
gullies
shoreline of Great Lakes
along the shoulders of roads
under downspouts
chemical weathering from acid rain
formation of caves
sinkholes
Physical weathering from frost
action:
• potholes
• cracks in sidewalks
Physical and chemical weathering
by:
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bacteria
fungi
worms
rodents
other animals