Weathering and Erosion
Mechanical Weathering
Chemical Weathering
Examine the illustration below that shows volcanic
mountain formation. Note that the volcanoes bring new
rock to the surface.
Weathering
• Mechanical or chemical weathering is a
surface process that breaks rocks into
smaller pieces.
• Freezing
• Thawing
• Oxygen in the air
• Plants
• Animals
• Weather
Mechanical Weathering
• Breaks rocks into smaller pieces without
changing them chemically.
• The small pieces are identical in
composition to the original rock.
• Ice wedging
• Living beings
Ice Wedging
• The freezing and thawing cycle breaks
up rocks.
• Ice wedging occurs when water seeps into
rock cracks and freezes. Interestingly,
water EXPANDS when it freezes. As the
water freezes in the rock crack, sections of
rock are broken off. Ice wedging is
common in areas where the climate
includes a cold season.
Ice Wedging
Note how the water can freeze and expand in rock
cracks.
Plants and animals
• Plants grow in inconvenient places. Their
roots grow into cracks in rocks where
water collects.
• Roots become thicker and longer exerting
pressure and wedging rock apart.
Note that the roots are creating large cracks in the
rock.
Plants and animals
• Gophers and prairie dogs weather rock,
burrowing in the ground.
• When they burrow through sediment, they
break the rocks.
Prairie dogs burrowing into the soil. Note the small
rocks that are now exposed
Interest Scientific Fact:
• Earthworms are a major factor in the
weathering of rock. Earthworms tunnel
through the soil looking for food. As they
tunnel, they bring rock flakes to the
surface and expose covered rock to the
weathering effects of air and water.
Earthworms
Abrasion
• Abrasion is the grinding of rocks. Abrasion
may occur because of the action of wind,
running water, waves, and gravity.
• Wind, running water, and waves push
smaller particles of rock into other rock
eventually causing pieces to chip away.
Rocks fall and tumble as gravity pulls them
down hill. When this happens, the rocks
chip or break apart.
Note how the wind has weathered the rock.
Remember this:
Rocks are weathered when
small pieces of rock are
pushed across other rock or
when a rock falls.
Abrasion
Abrasion
Abrasion occurs when
small pieces of rocks are
pushed into or across
another rock. Over time this
results in chipping or
wearing down of the rocks.
Rocks are weathered when
small pieces of rock are
pushed across other rock
or when a rock falls.
Abrasion
Interesting Scientific Fact:
The Grand Canyon
continues to be
weathered by the action
of the small grains of
rock that are carried
along by the Colorado
River.
Review 1
• Describe how rocks are mechanically
weathering.
• Explain how carbonic acid weathers rocks.
• Describe how soil forms. What factors are
important.
Agents of Erosion
• Erosion is the wearing away and removal
of rock and sediment.
• Agents:
• Gravity
• Ice
• Wind
• water
Gravity
• Gravity is a force that pulls every object
toward every other object.
• Gravity pulls everything on Earth toward
its center.
• Mass movement is when gravity causes
rock or sediment to move down a slope.
Mass Movement
• Creep process in which sediments move
slowly downhill.
• Common where freezing and thawing
occur.
Creep
Mass Movement
• Slump occurs when a mass of rock or
sediment moves downhill, leaving a curve
scar.
Slump
SLUMPS
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Slumps are:
often clay-rich (cohesive unit)
slow to rapid
have spoon-shaped failure surfaces
show clear scarp face at head (top)
end in earthflows at toe (bottom)
Slump
Slump
Mass Movement
• Rock Slides layers of rock break loose
from slopes and slide to the bottom.
• Million of cubic meters of rock roaring
down a mountain at speeds greater than
250 Km/h.
Rock Slides
Mass Movement
• Mudflows where heavy rains or melting
snow and ice saturate sediments.
• Mudflows is a mass of wet sediment that
flows downhill over the ground surface.
Mudflows
Mudflows
Mudflows
Ice
• Continental glaciers.
• Valley glaciers.
• Mountain glaciers.
• Ice can remove rock from mountaintops.
• Ice forms cirques.
• Ice can remove rock layers from land’s
surface.
Ice
Wind
• The erosion of the land by wind is called
deflation.
• Deflation can lower the land’s surface by
several meters.
• Abrasion is a form of erosion that can
make pits in rocks and produce smooth,
polished surfaces. ( deserts, cold regions
with strong winds).
Wind
Water
• Water that flows over Earth’s surface is
called runoff.
• Runoff causes erosion, especially if water
is moving fast.
• Sheet erosion is a thin sheet of water can
carry loose sediment grains with it,
causing erosion of the land.
Water
Water