Download Weathering

Guided Notes
Surface Processes
Weathering:
Physical Weathering
Chemical Weathering
Weathering Rates
Soil Formation
© K. Coder 2015
1) What is weathering?
• Weathering: The breakdown of rocks into
smaller particles called sediments
Physical
Types of Weathering: _________________
&
_________________
Chemical
2) What is physical weathering?
• Physical weathering: the breaking up of
rock into smaller particles without
changing the composition of the original
rock
3) What are examples of physical
weathering?
Type
Description
1)
Frost
wedging
Repeated freezing
and thawing of
water in the
cracks of rocks
Diagram
Common
Example
Pot holes
Frost Wedging
3) What are examples of physical
weathering?
Type
2)
Abrasion
Description
Bumping and
rubbing of rocks
as they collide.
Rocks become
smaller,
smoother, and
rounder.
Diagram
Common
Example
Rounded
pebbles
found near
water
Abrasion
3) What are examples of physical
weathering?
Type
3)
Root
action
Description
Roots grow
into and under
rocks. Roots
pry the rock
apart.
Diagram
Common
Example
Often
causes
damage in
concrete
like
sidewalks
Root Action
3) What are examples of physical
weathering?
Type
4)
Exfoliation
Description
Granite that is
uplifted to the
surface has a
great reduction
in pressure. The
surface of the
rock expands
and cracks into
slabs that break
away from the
solid surface.
Diagram
Common
Example
Yosemite
Half
Dome
Exfoliation
4) What is chemical weathering?
• Chemical weathering: a change in the
rock that forms a new compound
• Occurs on the surface of rock materials
• Dominates in warm and moist climates
5) What are examples of chemical
weathering?
Type
1)
Oxidation
Description
Iron atoms
combine with
oxygen to form
iron oxide (rust).
Diagram
Common
Example
The mineral
hematite
will rust
because it
contains
iron.
Oxidation
© K. Coder 2015
5) What are examples of chemical
weathering?
Type
2)
Carbonation
Description
Acid rain
dissolves rocks
containing the
mineral calcite.
Diagram
Common
Example
Limestone
bedrock
dissolves
when in
contact with
acidic
groundwater
forming
caves and
sinkholes.
5) What are examples of chemical
weathering?
Type
3)
Hydration
Description
Water weakens
some minerals
in rocks.
Diagram
Common
Example
Feldspar
becomes
clay after
long
exposure
to water.
✓ Review – Weathering: Identify each type of weathering
described below as physical or chemical. Description
1. A tree growing on bedrock extends its
root into a crack in the rock and splits
the rock.
Type of Weathering
✓ Review – Weathering: Identify each type of weathering
described below as physical or chemical. Description
2. The formation of caves as shown
below.
Type of Weathering
✓ Review – Weathering: Identify each type of weathering
described below as physical or chemical. Description
3. The enlargement granite bedrock
after water has seeped into the cracks
and frozen as shown below.
Type of Weathering
✓ Review – Weathering: Identify each type of weathering
described below as physical or chemical. Description
4. Rocks became smoothed with
rounded shapes as shown below.
Type of Weathering
✓ Review – Weathering: Identify each type of weathering
described below as physical or chemical. Description
5. The naturally occurring geologic
process shown below.
Type of Weathering
6) What are the factors that affect the
rate of weathering?
1. Climate:
• The graph below shows how
the climate you live in greatly
affects the type of weathering
that breaks down the rocks.
6) What are the factors that affect the
rate of weathering?
1. Climate:
a. Which type of weathering
would be prominent in a climate
with an average temperature of
-5˚C (24˚F) and an average
annual precipitation of 50 cm?
6) What are the factors that affect the
rate of weathering?
1. Climate:
b. Which type of weathering
would be prominent in a
climate with an average
temperature of 22˚C (70˚F)
and an average annual
precipitation of 125 cm?
6) What are the factors that affect the
rate of weathering?
1. Climate:
c. Which type of weathering can
be found at -10˚C (14˚F) with an
annual precipitation of 180 cm?
Why?
6) What are the factors that affect the
rate of weathering?
2. Exposed Surface Area: The more surface
area exposed while a particle is
weathering, the more it will weather.
(smaller particles weather faster!)
Think About It: Why does chewing
candy make it quicker to eat?
6) What are the factors that affect the
rate of weathering?
Example: Calculate the total surface area of
each diagram shown below.
Area of one side:
16 cm2
_________________
_________________
4 cm2
How many sides:
6
6
_________________
_________________
How many cubes:
1
8
_________________
_________________
Total surface area:
96 cm2
192 cm2
_________________
_________________
6) What are the factors that affect the
rate of weathering?
3. Mineral composition: Rocks weather at
different rates depending upon mineral
composition.
• Rocks composed of harder, more resistant
minerals will weather away slower.
• Rocks composed of softer, less resistant
minerals will weather away faster.
6) What are the factors that affect the
rate of weathering?
• Identify each of the rock layers below. Which
layer is least resistant to weathering? Which
layer is most resistant to weathering?
*Least resistant
A: _____________________
Shale
Limestone
B: _____________________
Dolostone
C: _____________________
Siltstone *Most resistant
D: _____________________
✓ Review – Weathering Rates & Soil
Formation
1. The diagram below shows an igneous rock that has undergone mainly
physical weathering into sand and mainly chemical weathering into clay.
Describe the change in temperature and moisture conditions that would
cause an increase in the rate of chemical weathering into clay.
✓ Review – Weathering Rates & Soil
Formation
2) In the diagram below, sample X and sample Y represent equal masses
of earth material which are weathering under the same conditions. The
samples have the same mineral composition.
Which sample will weather faster? Why?
✓ Review – Weathering Rates & Soil
Formation
3) The two photographs below show dates on tombstones found in a
cemetery in St. Remy, New York. The tombstones were 5 meters apart and
both faced north. Tombstone A had dates cut into the rock in 1922. Tombstone
B had dates cut into the rock in 1892.
Which statement best explains why the dates are more difficult to read on
tombstone A than on tombstone B?
a) Tombstone A is composed of minerals less resistant to weathering than
tombstone B.
b) Tombstone A has undergone a longer period of weathering than tombstone
B.
c) Tombstone A experienced cooler temperature than tombstone B.
d) Tombstone A was exposed to less acid rain than tombstone B.
✓ Review – Weathering Rates & Soil
Formation
4) The Niagara River began to flow over the Niagara Escarpment about
12,000 years ago when the last Pleistocene ice sheet melted and retreated
north from the Niagara Escarpment. Since that time, Niagara Falls has
eroded upriver, leaving a deep, steep-sided valley that is 11,000 meters
long. The top bedrock layer of the escarpment is the Lockport dolostone
which lies above the Rochester shale. The shale is more easily weathered
than the dolostone. This causes the dolostone to be undercut. As a result,
the dolostone breaks off in large blocks that tumble to the base of Niagara
Falls.
✓ Review – Weathering Rates & Soil
Formation
The block diagram shows the present position of Niagara Falls in relation
to the Niagara Escarpment. The cross section shows the general bedrock
structure of present-day Niagara Falls. The map shows measured changes
in the position of Niagara Falls since 1678.
© K. Coder 2015
✓ Review – Weathering Rates & Soil
Formation
Why has Niagara Falls eroded upriver?
✓ Review – Weathering Rates & Soil
Formation
6. The table below shows the results of an investigation of four different types
of rocks, weathering over a period of 30 minutes. Equal masses of similar
sized samples of rocks A, B, C, and D were placed in identical containers
half-filled with water. Each container was shaken uniformly for 5 minutes and
the remaining samples of rocks were removed from the water. Their masses
were determined and recorded in the data table. The remaining samples of
rocks were put back into the containers half-filled with water and the
procedure was repeated five times.
a. On the grid below, plot the data shown in the data table for each rock sample. Connect the
points for each rock sample with a smooth line. Label each line with the letter of the rock
sample.
Rock B
Rock D
Rock A
© K. Coder 2015
Rock C
✓ Review – Weathering Rates & Soil
Formation
b. Which rock sample was most resistant to the
abrasive action caused by the shaking of the
container? Justify your answer.
✓ Review – Weathering Rates & Soil
Formation
c. According to the data table, the mass of rocks
samples remaining at the end of 20 minutes was
different for each sample. Explain why this likely
occurred.