WELCOME TO OUR
EARTH SCIENCE
CLASS
WEATHERING
AND
EROSION
WEATHERING
• Weathering is the breaking down or
dissolving of rocks and minerals on earths
surface. Water, ice, acids, salt, plants,
animals, and changes in temperature are all
agents of weathering.
MECHANICAL WEATHERING
• Mechanical weathering is the disintegration of rock into
smaller and smaller fragments. Frost action is an effective form
of mechanical weathering.
• Mechanical weathering, also called physical weathering,
causes rocks to crumble. Water seeps into cracks and crevices
in rock.
• Mechanical weathering also occurs as the rock heats up and
cools down. The changes in temperature cause the rock to
expand and contract.
CHEMICAL WEATHERING
• Chemical weathering changes the materials that make up rocks
and soil. Sometimes, carbon dioxide from the air or soil
combines with water. This produces a weak acid, called carbonic
acid, that can dissolve rock.
• Chemical weathering transforms the original material into a
substance with a different composition and different physical
characteristics. The new substance is typically much softer and
more susceptible to agents of erosion than the original material.
BIOLOGICAL WEATHERING
• Biotic weathering is any type of weathering that is caused by
living organisms. Most often the culprit of biotic weathering are
plant roots. In the process they act as a wedge, widening and
extending the cracks.
• Biological weathering also means organic weathering. It is the
disintegration of rocks as a result of the action by living
organisms. Plant and animals have a significant effect on the
rocks as they penetrate or burrow into the soil respectively.
EROSION
WHAT IS EROSION?
• Erosion is the action of surface processes that remove, soil,
rock, or dissolved material from one location on the Earth’s
crust to another location.
• The process of erosion moves bits of rock or soil from one
place to another.
• Performed by water, wind, or ice.
• Water Erosion
• Rain carries away soil and slowly washes away rock particles
or fragments.
• Rushing rivers and streams create larger valleys due to the
wearing of their banks.
• Water changes the shape of coastlines as waves constantly
crash against the shores. Rocks turn into pebbles and pebbles
turn to sand.
• Ocean waves also erode seaside cliffs. It creates holes that
form caves.
• Wind Erosion
• It carries sand , volcanic ash, and dust from one place to
another.
• Major geomorphological force in arid and semi-arid
regions.
• Wind blows sand that turns into towering dunes.
• Windblown sand blasts against rock with strong force
enough to wear the soft rock away slowly.
• Deflation Wind Erosion and Abrasion Wind Erosion
• Ice or Glacial Erosion
• Glaciers moves slowly downhill and across the land
causing the land to erode.
• The rocks carried by a glacier contact the ground,
eroding both the ground and the rocks.
• Abrasion/Scouring, Plucking, and Ice Thrusting
•Human Activities
•Deforestation
•Overgrazing
•Faulty Methods of Agriculture
FACTORS THAT AFFECT THE RATE OF
WEATHERING
• CLIMATE
The amount of water in the air and the temperature of an
area are both part of an area’s climate. Moisture speeds up
chemical weathering. Weathering occurs fastest in hot, wet
climates. It occurs very slowly in hot and dry climates.
Without temperature changes, ice wedging cannot occur. In
very cold, dry areas, there is little weathering.
FACTORS THAT AFFECT THE RATE OF
WEATHERING
• SURFACE AREA
Most weathering occurs on exposed surfaces of rocks and
minerals. The more surface area a rock has, the more
quickly it will weather. When a block is cut into smaller
pieces, it has more surface area. So, therefore, the smaller
pieces of a rock will weather faster than a large block of rock.
FACTORS THAT AFFECT THE RATE OF
WEATHERING
• ROCK COMPOSITION
Some minerals resist weathering. Quartz is a mineral
that weathers slowly. Rocks made up of minerals
such as feldspar, calcite, and iron, weather more
quickly.
FACTORS THAT AFFECT THE RATE OF
WEATHERING
• POLLUTION
This speeds up weathering. Factories and cars release
carbon dioxide and other gases into the air. These gases
dissolve in the rainwater, causing acid rain to form. Acid rain
contains nitric and sulfuric acids, causing rocks and minerals
to dissolve faster.
WHAT TO DO?
• Sequence the processes by which factors in mechanical weathering break
down rocks and minerals. Number the steps in each process 1-4
• Temperature
___ Freezing water exerts pressure on the rocks and make them split
___ Water collects in the cracks of rocks and rock layers.
___ Water thaws and the cycle, called frost wedging, repeats.
___ Water expands as it freezes.
WHAT TO DO?
• Sequence the processes by which factors in mechanical weathering break
down rocks and minerals. Number the steps in each process 1-4
• Pressure
___ Successive layers of rock are stripped away in a process called exfoliation
___ The bedrock surface expands and long cracks form parallel to the surface
of the rock.
___ The overlying rock layers are removed and the pressure on the bedrock is
reduced
___Bedrock at great depths is under pressure from overlying rock layers.
WHAT I LEARNED?
•Is erosion a purely destructive force,
or does it have constructive aspects as
well? Explain your answer and give
examples.
