 Rocks and Weathering
 Chapter 2
 Section 2
 6th Grade Team
 Standard
 S 6.2.aStandard
S. 6.2 Topography is reshaped by the weathering of rock and soil and by the
transportation and deposition of sediment.
S.6.2.a Students know water funning downhill is the dominant process in
shaping the landscape, including California’s landscape.
Weathering and Erosion (Input)
 Weathering – the process that breaks down rock and other substances at
Earth’s surface. (NTG)
 Heat, cold, water, ice, oxygen and carbon dioxide all contribute to weathering
 Repeated freezing and thawing can crack rocks into small pieces.
 You do not have to look at the mountains to see weathering. It occurs on your
bike as they begin to rust, or the paint peels, sidewalks crack, and potholes
form.
Weathering and Erosion (Input)
 Erosion- the transportation of sediment by wind, water, ice, or gravity. (NTG)
 Topography is reshaped by weathering and erosion. These processes work
together continuously to wear down and carry away the rocks at Earth’s
surface. (NTG).
 Uniformitarianism- the same processes that operate today operated in the
past. What happens today, happened thousands of years ago. (NTG)
 Mechanical Weathering
 Mechanical Weathering- in which rocks are physically broken into smaller
pieces. (NTG)
 It acts slowly, but over time they break down even the biggest, hardest rocks.
It can wear away whole mountains.
 The causes of mechanical weathering include freezing and thawing, release
of pressure, plant growth, actions of animals, and abrasion (NTG)
 Abrasion- grinding away of rock by rock particles carried by water, ice, wind,
or gravity.
Mechanical Weathering (Input)
 Cool climates- freezing and thawing of water
 Ice Wedging- water expands when it freezes and acts as a wedge. Wedges of
ice in rocks widen and deepen cracks. (NTG)
 Release of Pressure
 Freezing and Thawing
 Animal Actions
 Plant Growth
 Abrasion
 Pages 58-59
 Chemical Weathering
 Chemical Weathering- the process that breaks down rock through chemical
changes. (NTG)
 The causes of chemical weathering include the action of water, oxygen,
carbon dioxide, living organisms, and acid rain. (NTG)
 Chemical weathering can produce new minerals as it breaks down rocks.
 Chemical weathering creates holes or soft spots in rocks, so they break apart
easier.
 Chemical weathering and mechanical weathering work together. Mechanical
will break rock into pieces and more surface area becomes exposed to
chemical weathering.
 Chemical Weathering
 Water- water weathers rock by dissolving it. It mixes uniformly throughout
the water to make a solution.
 Oxygen- Iron combines with oxygen in the presences of water in a process
called oxidation. (NTG). It produces rust.
Rust makes rock soft and crumbly and gives it a red or brown color.
 Carbon Dioxide- it dissolves in rainwater and in water that sinks through air
pockets in the soil. It creates a weak acid called carbonic acid. Carbonic acid
weathers marble and limestone.
 Chemical Weathering
 Living Organisms- Plants root grow and produce weak acids that slowly
dissolve rock around the root. Lichens (plantlike organisms on rocks) also
produce weak acid.
 Acid rain- Burning fuels such as coal, oil, and gas for energy can pollute the
air with sulfur, carbon and nitrogen compounds. These compounds reach
with water vapor in the clouds and produce acid rain. They mix with
raindrops and fall as acid rain.
 Rate of Weathering
 The most important facts that determine the rate at which weathering occurs
are the type of rock and climate. (NTG)
 Type of Rock
The minerals that make up the rock determine how fast it weathers.
Permeable- that a materials is full of tiny, connected air spaces that allow water
to seep through it. They will weather faster because water seeps into the air spaces
and dissolves and removes material brown down by weathering.
 Rate of Weathering
 Climate- the average weather conditions in an area
 Chemical and mechanical will occur fast in WET climates.
 Rainfall results in freezing and thawing
 Granite weathers slowly in cool climates that is often used in building stone.
In HOT and WET climates granite weathers more rapidly and crumbles apart.
 Checking for Understanding
What is weathering?
What is erosion?
What is Ice Wedging?
What grinds away rock by rock particles carried by wind, ice, water or gravity?
 List the types of mechanical weathering
 Guided Practice
Independent Practice
 GP
NTG page 38-39 # 1-7
IP
NTG page 40-41 #8-25