Transcript physical and chemical weathering

Investigation 3:
Rocks and
Weathering
Key Question
• How do different types of rocks
weather?
Weathering
• Is the breakdown of
rock into smaller and
smaller pieces.
• Undergo weathering
either by mechanical
or chemical means.
Mechanical Weathering
• Also called physical
weathering.
• Is simply the
breakdown of rock
into smaller pieces
by physical means.
• These physical
means include ice,
wind, water, gravity,
plants, and animals.
Types of Mechanical
Weathering
1. Ice
– Water seeps into a crack in a rock during
warm weather and then freezes during cold
weather.
– The ice expands, pushing against the sides of
the crack, forcing it to open wider.
– This is called ice wedging.
2. Wind, Water, and Gravity
• Abrasion
– Is the action of rocks and sediments grinding against
each other and wearing away exposed surfaces.
– Rocks and pebbles abrade by rolling along the
bottoms of a stream, river, or the ocean.
– Wind could blow small particles of sand against rock
surfaces.
– Rocks fall from higher altitudes, crash against the
floor or each other and break down.
3. Plant Weathering
• Plant send their roots into existing cracks
in rocks. As the roots get bigger the crack
gets bigger, eventually breaking the rock
in two.
• This can affect sidewalks and paved
driveways.
4. Animal
• Earthworms- burrow
through the soil and
move soil particles
around. This exposes
fresh surfaces to continue
weathering.
• Ants, mice, rabbits etc.
contribute to the mixing
and digging that aids in
weathering.
Pictures of Mechanical
Weathering
Chemical Weathering
• Is the chemical
breakdown of rocks
and minerals into
new substances.
• Most common
agents are: water,
weak acid, air, and
soil.
Types of Chemical Weathering
1. Water
-
It will breakdown almost any material over time.
By dropping a piece of chalk in water it will dissolve very
quickly.
2. Acid Precipitation
- Carbonic acid found in rain and snow can rapidly
weather rock
- Comes from natural sources such as volcanoes
- Comes from the burning of fossil fuels such as coal and
oil. It gives off gases that combine with water in the
atmosphere.
Cont. Chemical Weathering
3. Acid in Ground Water
- Increase carbonic or sulfuric acid in a water supply
can cause the formation of huge underground caves.
- Usually occurs in areas of large limestone deposits.
4. Acids in living things (Lichens)
- Lichens
- symbiotic relationship between a fungus and algae.
- found growing on rocks and trees
- produce organic acids that eat away at the surfaces.
Cont. Chemical Weathering
5. Oxidation
- Air reacts with iron causing a chemical reaction.
- Rust is the end product
- Can occur in rocks with a high iron content.
Pictures of Chemical
Weathering
•
•
•
• Karst
The Earth System and
Weathering
– Landform formed by chemical weathering.
– Animals, humans, fossil fuels add carbon dioxide into the
atmosphere creating acid rain.
– This acidic water travels through the water supply and breaks
down rocks.
– In areas of pure limestone the acid breaks down the rock
underground causing the karst.
– This lead to the formation of underground caverns.
– This is also called a sinkhole.