Weathering, Erosion and
Natural Catastrophes
Weathering
• Weathering is the process that
breaks down rock and other
substances at Earth’s surface.
Erosion
• Erosion is the movement of rock
particles by wind, water, ice, or
gravity.
Working together
Weathering and erosion work
together continuously to wear
down and carry away the rocks at
Earth’s surface. Weathering
breaks rock down and erosion
carries it away.
2 Types of Weathering
• There are 2 types of
weathering:
• Mechanical and Chemical
Working together
• As mechanical weathering breaks
rock into pieces, more surface
area becomes exposed to
chemical weathering. So, they
also work together.
Mechanical Weathering
• The type of weathering in which
rock is physically broken into
smaller pieces is called
mechanical weathering.
Agents of mechanical weathering
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Freezing and thawing
Release of pressure
Action of animals
Growth of plants
Abrasion - rock particles carried by wind,
water, ice and gravity.
• Water expands when it freezes, and acts
as a wedge.
• This process is called ice wedging.
Mechanical weathering
Ice Wedging
Chemical Weathering
• Chemical
weathering is
the process that
breaks down
rock through
chemical
changes.
Agents of chemical weathering
The agents of chemical weathering
include:
• water
• Oxygen (oxidation is a reaction w/ O2)
• carbon dioxide ( carbonic acid)
• living organisms( plant roots produce
weak acids)
• acid rain
Weathering from acid rain
Rates of weathering
• The most important factors that
determine the rate at which weathering
occurs are the type of rock and climate.
• Ex: Some rock weathers easily because it
is permeable, which means that it is full of
air spaces that water gets through.
Chemical weathering
• Water is the most important agent of chemical
weathering.
• Water weathers rock by dissolving it.
• The oxygen in air is an important cause of
chemical weathering.
• Plant roots produce weak acids that slowly
dissolve any rock around the roots.
• Lichens also produce a weak acid that weathers
rock.
• Acid rain causes very rapid chemical
weathering.
Erosion
• The material moved by erosion is
sediment.
• When the agents of erosion lay down
sediment, deposition occurs.
– Deposition changes the shape of the land.
Erosion
More erosion
Cycle of erosion
• Weathering, erosion, and deposition
act together in a cycle that wears down
and builds up Earth’s surface.
• Erosion and deposition are at work
everywhere on Earth. Sometimes, they
work slowly. At other times, they work
more quickly.
Agents of Erosion
Water
• The major agent of erosion
• Shapes Earth’s land surface
Runoff Erosion
Gully
Rill
Wave Erosion
River and Stream Erosion
Glacial Erosion
Caused by gravity
pulling glacier down
Wind Erosion
•Wind itself is the weakest
cause of erosion.
•Greatest impact is on an
area that has few plants to
hold dry soil in place
• Gravity is the force that moves rock
and other materials downhill.
• Gravity causes mass movement, any one
of several processes that move sediment
downhill.
• Mass movement can be rapid or slow.
Mass Movements
The different types of mass movement
include:
• Landslides – rock and soil slide quickly
down a steep slope.
• Mudslides -the rapid movement of a mixture
of water, rock, and soil.
• Slump – a mass of rock and soil suddenly
slips down a slope in one large mass.
• Creep – very slow downhill movement of
rock and soil.
Landslides
Mudslide
Slump
Creep
Natural catastrophes
• A natural catastrophe/hazard is an
event that results from Earth
processes and that can cause
damage and endanger human life.
And the natural catastrophes are…
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droughts
wildfires
floods
the different types of mass movement
tsunamis
hurricanes
tornadoes
earthquakes
volcanoes
other storms
Volcano
Earthquake
Tornado
Hurricane
Catastrophic events can affect Earth in
several ways.
• Catastrophic events that result from
surface processes may speed up erosion
and deposition.
• Catastrophic events resulting from
processes inside Earth change the crust
itself (volcanoes).
People, People, People
• Where people locate their activities can
increase the damaging effects of natural
hazards.
• How people use land also alters Earth
systems in ways that may cause
catastrophic events.