Breaking it Down
Weathering & Erosion
4/30/15
Breaking it Down
Key Question: What is weathering, and what
are some examples?
Initial Thoughts:
Evidence: Weathering
• Large rocks and landforms first need to be
broken down into smaller pieces in order
to be worn away by erosion.
• This is accomplished by weathering - the
breaking down of rock by chemical or
mechanical processes
Mechanical Weathering
Definition: Breaking up of rock by physical
forces, such as the action of wind and
moving water.
The rock itself does not change; it just gets
broken into smaller pieces.
Process Name
Frost Wedging
Where does it
occur?
What is it?
• Go to the website, which can be found on
my links page under “Mechanical
Weathering, and click “NEXT” twice:
http://ees.as.uky.edu/sites/default/files/ele
arning/module07swf.swf
Check yourself
Process Name
Where does it occur?
What is it?
Frost Wedging
Cold, moist mountains
Water expands when it freezes,
breaking apart rocks
Exfoliation
Mountains with igneous
rock
Igneous rock pushes up, breaking
off big sheets of rock
Thermal
expansion
Desert regions
Crystals in rocks expand & contract
with extreme temperature changes,
weakening & breaking the rock.
Crystal Growth
Coastal & desert regions
Salt crystals grow and weaken &
loosen rocks
Tree roots
Warm, moist regions that
support forests
Tree roots wedge into rocks and
break them apart
Abrasion
Wherever there’s water,
wind, or ice
Rocks falling and breaking or
wearing down by the direct actions
of other rocks
Exfoliation or unloading rock breaks off into leaves or sheets
along joints which parallel the ground
surface;
caused by expansion of rock due to uplift
and erosion; removal of pressure of deep
burial
 Organic activity (TREES/root-pry,
burrowing animals, human activities)
 Abrasion & Gravity: rocks falling
and colliding with other rocks
 Contraction due to crystallization
The surface pattern on this
pedestal rock is honeycomb
weathering, caused by salt
crystallisation. This example is
at Yehliu, Taiwan.
Salt
weathering
of building
stone on the
island of
Gozo, Malta
Chemical Weathering
Definition: wearing away of rocks by
chemical processes, such as dissolving
or oxidation.
• It’s a breaking down process
Chemical Weathering
Process Name
Dissolution
Oxidation
Hydrolysis
Where does it
occur?
What is it?
Dissolving
• Acids or water dissolve the rocks.
• Sources: Acid rain from pollution, plant roots,
water & limestone (example caves),
 Water: Dissolves minerals out of rocks
making them weaker
Chemical weathering
Acid: Dissolves minerals in rocks
examples: carbonic acid, acid rain, and
plant acid
Lichens such as
these growing on the
rocks in the picture
can produce weak
acids that react with
the rock.
3000 year old Egyptian Obelisk
3000 year old Egyptian Obelisk
after 100 years in NY
Oxidation
• Oxidation or rusting - some minerals
contain metals, like Iron or sulphur, that
can rust when exposed to oxygen. Just
like an old car, nail, or piece of metal left
outside.
Oxidation
Evidence 2: Weathering Lab
Each group will be assigned two of the 8
treatment groups:
1. Crushed tablet in water
1. Whole tablet in water
2. Crushed tablet in heated water
2. Whole tablet in heated water
3. Crushed tablet in vinegar
3. Whole tablet in vinegar
4. Crushed tablet in heated vinegar
4. Whole tablet in heated vinegar
Analysis Q’s
1. Compare & contrast mechanical and
chemical weathering. (a venn diagram or
chart is o.k.)
2. Which of the treatment groups in the lab
represented mechanical weathering?
3. Why do you think the obelisk (slide 17)
showed more weathering during the 100
years in New York than it did in the 3,000
years it was in the desert in Egypt?
Summary
What did you think about how weathering
works before this lesson?
What did you learn about how weathering
works from this lesson? (Minimum of 3
sentences!!!)
What are some further thoughts or questions
you have about how weathering works?
Reflection
• Explain how mechanical and chemical
weathering are similar to the process of
mechanical & chemical digestion. Use
words, pictures, or both.
Big Idea
• Rock landforms can be broken down by
the natural processes of mechanical &
chemical weathering.