Download Processes of Change

Weathering:
Processes of Change
EQ:
How does weathering
occur?
Weathering
• Describe three ways
abrasion occurs in nature.
• List three things that
cause chemical
weathering of rocks.
• Describe the similarity in
the ways tree roots and
ice mechanically weather
rock.
• Describe five (5) sources
of chemical weathering.
The Processes of Change
Lesson 18
Processes of Change (5)
• Weathering and erosion wear down,
deposition fills in Earth’s surface.
• Weathering is the slow wearing away or
breaking down of objects exposed to
Earth’s atmosphere
• Two kinds of weathering act on Earth’s
surface
– Mechanical weathering
– Chemical weathering
Weathering
• Weathering is the process by which rock
materials are broken down by the action of
physical or chemical processes.
• Mechanical weathering is the breakdown of rock
into smaller pieces by physical means. (ice,
wind, water, gravity, plants, animals)
• Chemical weathering is the process by which
rocks break down as a result of chemical
reactions. Water, weak acids, and air can cause
chemical weathering.
Mechanical Weathering (4)
• When objects are broken down into small
pieces but their chemical makeup doesn’t
change
• Wind and moving water are two main
causes of mechanical weathering
• Repeated changes in temperature (freeze,
melt, freeze, melt again)
Chemical Weathering (5)
• Material of an object is changed
• Produces underground caverns
• Statue of Liberty needed repairs because
of chemical weathering
• Examples:
– Rust
– Acid rain
Erosion (5)
• The natural moving of material from one
place to another
• Erosion transports weathered rock material
• Causes of Erosion:
– Moving water
– Gravity
– Wind
– Glaciers (moving rivers of ice)
– Waves
Deposition (5)
• Land torn down in one place is “deposited”
in another place
• Gravity can cause a landslide moving
mud, rock and soil down a hill
• Wind erosion can move sand and deposit
it in another area
• Glaciers (rivers of ice) scrape rocks off the
land and moves them downhill
• Glaciers will stop
moving and even
retreat and cut a
steep U-shaped
valley in the land
• Erosion caused by
mountain rivers form
V-shaped valleys
• Hurricanes create
waves that erode
beaches and cliffs
• Breaking of waves on
a beach can wear it
away. The larger the
waves, the faster is
the rate of erosion.
6 Agents of Mechanical Weathering
• 1. Ice – water seeps into cracks during warm
weather. When the temperature drops, the
water freezes and expands, causing the ice to
push against the sides of the crack. This causes
the crack in the rock to widen.
– Abrasion – the grinding and wearing away of rock
surfaces through mechanical action of other rock or
sand pebbles.
– The three ways that can cause abrasion are wind,
water, and gravity.
Abrasion
• Abrasion – the grinding and wearing
away of rock surfaces through
mechanical action of other rock or sand
pebbles.
– The three ways that can cause
abrasion are wind, water, and gravity.
Three Causes of Abrasion
• 2. Water – as rocks and pebbles roll along
the bottom of flowing water, they bump and
scrape against each other, causing these
rocks to become rounded and smooth.
• 3. Wind – wind blows sand and silt against
exposed rock eventually wearing away the
rock’s surface.
• 4. Gravity – rocks grind against each other
during a rock slide, creating smaller and
smaller rock fragments. Anytime one rock
hits another rock, abrasion takes place.
Plants and Animals
• 5. Some plants can easily break rocks. The
roots grow through existing cracks in rocks. The
growth causes the root to expand, forcing the
crack to widen. The force can eventually split
the rock apart.
• 6. Animals that live in the soil (moles, prairie
dogs, insects, worms, gophers), cause a lot of
weathering. By burrowing in the ground, these
living creatures brake up soil and loosen rocks
to be exposed to further weathering.
3 Agents of Chemical Weathering
• Common agents of chemical weathering are
water, weak acids, and air.
• These agents weaken the bonds between
minerals grains of the rock.
• 1. Water – can cause rock to be broken down
and dissolve. Can take thousands of years to
take place.
• 2. Air – the process of oxidation is a chemical
reaction in which an element (iron) combines
with oxygen, causing rust.
• 3. Weak Acids - acid precipitation, acids in
groundwater, acids in living things.
Three Sources of Weak Acids
• Acid Precipitation – rain, sleet, or snow that
contains a high concentration of acid.
Normal precipitation is acidic, acid
precipitation contains more acid than normal.
• Acids in Groundwater – carbonic acid or
sulfuric acid reacts with rocks in the ground,
causing a chemical reaction, eating away at
the rock.
• Acids in Living Things – Lichens produce
acids that slowly break down rock.
Summary
• Ice wedging is a form of mechanical weathering
in which water seeps into rock cracks and then
freezes and expands.
• Wind, water, and gravity cause mechanical
weathering by abrasion.
• Animals and plants cause mechanical
weathering by turning the soil and breaking
apart rocks.
• Water, acids, and air chemically weather rock by
weakening the bonds between mineral grains of
the rock.
Quick Check
Which of the following things cannot cause
mechanical weathering?
•
•
•
•
A. water
B. acid
C. wind
D. animals
Quick Check
Which of the following is a type of frost
action?
•
•
•
•
A. abrasion
B. oxidation
C. ice wedging
D. gravity
Quick Check
Which of the following types of chemical
weathering causes a karst landscape,
such as a cavern?
•
•
•
•
A. lichens
B. acid precipitation
C. acids in groundwater
D. water
Quick Check
How do lichens slowly break down a rock?
•
•
•
•
A. by abrasion
B. by mechanical means
C. by ice wedging
D. by chemical means
Quick Check
Which of the following will most likely
experience oxidation?
•
•
•
•
A. tennis ball
B. aluminum can
C. wooden fence
D. Bicycle tire
Quick Check
1. The grinding and wearing away of
rock surfaces through the
mechanical action of other rock or
sand particles
2. Rain, sleet, or snow that contains a
high concentration of acids
3. The process by which rocks break
down as a result of chemical
reactions
4. The breakdown of rock into smaller
pieces by physical means
5. A chemical reaction in which an
element, such as iron, combines with
oxygen to form an oxide
6. The process by which rock materials
are broken down by the action of
physical or chemical processes
a. mechanical
weathering
b. oxidation
c. weathering
d. acid
precipitation
e. abrasion
f. chemical
weathering