Weathering,
Erosion,
and
Soil Formation
Standard: S6E5
Students will investigate
the scientific view of how the earth’s surface is formed.
d. Describe processes that change rocks and the
surface of the earth.
e. Explain the effects of physical processes (plate
tectonics, erosion, deposition, volcanic
eruption, gravity) on geological features
including oceans (composition, currents, and
tides).
h. Describe soil as consisting of weathered rocks
and decomposed organic material.
i. Explain the effects of human activity on the
erosion of the earth’s surface.
j. Describe methods of conserving natural
resources such as water, soil, and air.
Rocks & Weathering
Essential Questions
1. What is weathering?
2. What is erosion?
3. What is the difference between
weathering and erosion?
Weathering
• The process that breaks down rock and
other substances at Earth’s surface.
• Items contributing to weathering:
– Heat, cold, water, and ice
– Oxygen and carbon dioxide in the
atmosphere
Types of Weathering
• Mechanical Weathering – rock is
physically broken into smaller pieces.
– The smaller rock pieces have the same
composition as the rock they come from.
• Chemical Weathering – rocks break
down through chemical changes.
– Produces new minerals as it breaks down.
– Creates holes or soft spots in rock so the rock
breaks apart more easily.
Mechanical Weathering:
• Causes of mechanical weathering include:
– Freezing and thawing
– Release of pressure
– Plant growth
– Actions of animals
– abrasion
See Page 178-179 in
Science Textbook
Mechanical Weathering
• The causes of mechanical
weathering include freezing and
thawing, release of pressure, plant
growth, actions of animals, and
abrasion. See text p. 179
• Abrasion – the grinding away of rock by
rock particles carried by water, ice, wind,
or gravity.
Mechanical Weathering
• Ice wedging- wedges of ice in rocks
widen and deepen. When the ice melts,
the water seeps deeper into the cracks.
With repeated freezing and thawing, the
cracks slowly expand until pieces of rock
break off.
Chemical Weathering
• Causes of chemical weathering include:
– The action of water
– oxygen
– carbon dioxide
– living organisms
– acid rain.
See science
textbook p. 180-181
How does water affect weathering?
• Rainwater can dissolve
minerals that bind rock
together.
Mudpots: Mudpots are similar to hot springs
except that the groundwater has dissolved
rocks into clay, creating mud. High levels of
acid in the water help to dissolve the rocks
quickly. The color of the mud often varies
depending on the minerals that are in the
rocks.
http://www.grandeguides.com/images/05716_nps_mud_pot_near_sulfur_cauld
ron__mud_volcano_area__harlan_kredit__1974.jpg
Weathering and Erosion
• The forces that wear down mountains also
cause bicycles to rust, paint to peel,
sidewalks to crack, and potholes to form.
• These forces break rocks into smaller and
smaller pieces.
Two kinds of Weathering:
1. Mechanical weathering- where rock is
physically broken into smaller pieces.
2. Chemical weathering- Process that breaks
down rock through chemical changes. (causes
of chemical weathering include the action
of water, oxygen, carbon dioxide, living
organisms, and acid rain)
Chemical Weathering
• Can produce new minerals as it breaks
down rock. (EXAMPLE: granite is made of
minerals, including feldspar, quartz, and
mica.) As a result of chemical weathering
granite eventually changes the feldspar
minerals to clay minerals.
• Creates holes or soft spots in rock so the
rock breaks apart more easily.
Chemical Weathering & Water
• Water weathers rock by dissolving it.
• When the rock dissolves in water, it mixes
uniformly throughout the water to make a
solution.
• Over time, many rocks will dissolve in
water.
Chemical Weathering & Oxygen
• Iron combines with oxygen in the presence
of water in a process called oxidation.
This process is called rust. (Example: you
leave your bicycle outside in the rain,
oxygen combines with the iron parts and
rust takes place.)
How does oxygen and carbon
dioxide in the atmosphere affect
weathering?
Chemical Weathering &
Carbon Dioxide:
• Carbon dioxide dissolves in rainwater and
in water that sinks through air pockets in the
soil. The result is a weak acid called
carbonic acid.
• Carbonic Acid- easily weathers rocks
such as marble and limestone.
Chemical Weathering &
Living Organisms
• Small seed sometimes fall on rocks
and sprout.
• The roots push into cracks in the
rock.
• As the roots grow, they produce
weak acids that slowly dissolve
rock around the roots.
• Lichens – plantlike organisms that
grow on rocks– also produce weak
acids that chemically weather rock.
Lichens—break down rock and
other materials.
Chemical Weathering &
Acid Rain
• Burning of coal, oil, and gas
for energy pollutes the air with
sulfur, carbon, and nitrogen.
These compounds react
chemically with the water
vapor in clouds---forming
acids.
• These acids mix with
raindrops and fall as acid rain.
• Acid rain causes very rapid
chemical weathering.
Rate of Weathering:
• The most important factors that determine the
rate at which weathering occurs are the type of
rock and the climate.
• Type of Rock- minerals making up a rock
determines how fast it will weather.
– Permeable (material full of tiny air spaces that allow
water to seep through) rock weathers at a fast rate
because water seeps through the spaces and it
dissolves.
• Climate – average weather conditions. Both
chemical and mechanical weathering occur
faster in wet climates. Rainfall provides water
needed for chemical changes as well as for
freezing and thawing.
Two types:
Definition:
The processes that
break down rock and
other substances at
Earth’s surface.
Mechanical:
1) Mechanical - rock is
physically broken into smaller
pieces.
2) Chemical - rock is broken
down through chemical
changes.
Weathering
abrasion
ice wedging
Chemical:
water, oxygen (oxidation), carbon
dioxide, living organisms, acid rain.
Examples:
Characteristics:
Magma
lava
melting
What is Erosion?
• The removal of rock particles by wind, water, ice,
or gravity.
• Weathering and erosion work together with
deposition continuously to wear down and carry
away and build up the rocks at Earth’s surface.
• The weathering & erosion we see today also
shaped Earth’s surface millions of years ago.
Characteristics
Definition:
Works with weathering to
continuously wear down and
carry away rocks at Earth’s
surface.
The removal of rock
particles by wind, water, ice,
or gravity.
Works with weathering to
continuously wear down and
carry away rocks at Earth’s
surface.
Uniformitarianism - states
that the same processes that
operate today operated in the
past.
Erosion
Wave action, wind
Mass Movement
Landslides
Dump trucks
Mudflows
Bulldozers
Slump
Creep
See textbook p
205-207
Examples:
Non-Examples: