Download Weathering Study Guide

Mechanical Weathering
Mechanical Weathering
Study Tip
Mechanical Weathering (aka physical weathering) breaks
rock into smaller pieces. Rock changes physically, without
changing its composition. Smaller pieces have the same
minerals in the same proportions as the original rock.
Here are some forms of mechanical weathering:
•
Remember that mechanical
weathering has 2 main causes: natural
forces (wind, water, ice, and gravity)
and life (plants, animals, and
humans).
Earth Science
Surface Processes and Landforms
Ice Wedging: main form of mechanical weathering in any climate that regularly cycles above and
below the freezing point
Ice Wedging
•
o
Breaks apart large amounts of rock
o
Common in Earth’s polar regions and mid-latitudes, and at higher elevations
Abrasion: one rock bumps against another rock; smoothens sharp or jagged rocks
o
Caused by gravity as a rock tumbles down a mountainside or cliff
o
Caused by moving water as particles in the water collide and bump against one another
o
Caused by strong winds carrying pieces of sand which can sandblast surfaces
o
Caused by ice in glaciers which carries many bits and pieces of rock. Rocks embedded at the
bottom of the glacier scrape against the rocks below
•
Organisms: plants and animals can cause mechanical weathering
o
E.g. plant’s roots grow into a crack or fracture in rock and gradually grow larger, wedging open
the crack
o
E.g. burrowing animals can break apart rock as they dig for food or make living spaces for
themselves
•
Humans: digging or blasting into rock to build homes, roads, subways; quarrying stone
Chemical Weathering
What is Chemical Weathering?
•
Study Tip
Chemical Weathering is the form of weathering
where a mineral changes into a different type of
mineral through chemical reactions.
•
Think about why the materials
used for storage are often
waterproof and/or airtight.
Any mineral created within Earth’s mantle is exposed to high temperatures and it needs to
adjust to cooler temperatures once it rises to the surface. Therefore, a series of chemical
reactions changes its composition.
•
Clay is one substance formed by chemical weathering. It’s common because it is very stable
for silicate minerals.
What are the Different Forms of Chemical Weathering?
Water
Carbonic acid
Oxygen
Water is a polar molecule meaning
Carbonic acid formed from
Oxidation is a process
that it has positive and negative
interaction between CO2
where O2 reacts with
fields that bind to opposite charges.
and water. Carbonic acid
another element
Hydrolysis is the process where
helps to dissolve rock
Rust is created from the
water separates a mineral’s ions.
particles.
oxidation of iron oxide.
Earth Science Study Guide
Surface Processes and Landforms
How Do Plants and Animals React to Chemical Weathering?
•
Plants increase the rate of chemical weathering because elements are exchanged once plant roots
take in soluble ions.
•
Bacterial decay involves the use of carbon dioxide in respiration.
Does Mechanical Weathering Affect Chemical Weathering?
•
Mechanical weathering increases the rate
of chemical weathering because as rock
splits, its surface area increases. With
more surface area, chemical weathering
will have a greater effect on the rock.
Concept Check
•
Describe what chemical weathering is and explain why it exists.
•
Why is water able to cause chemical weathering?
•
Why are plants and animals able to increase the rate of chemical weathering?
•
Explain why mechanical weathering can increase the rate of chemical weathering.
Influences on Weathering
Rock and Mineral Type
•
Different rock types weather at different rates
•
Certain types of rocks are very resistant to
weathering
o
Study Tip
To help remember how climate
affects weathering, remember the
letter “w.” Wetter, warmer
climates have greater weathering.
Earth Science
Surface Processes and Landforms
Igneous rocks, especially intrusive igneous rocks
such as granite, weather slowly because water cannot
easily penetrate them
o
Other types of rocks, such as limestone, are easily
weathered because they dissolve in weak acids
•
Rocks that resist weathering remain at the surface and
form ridges or hills
•
Different minerals also weather at different rates
o
Some minerals in a rock might completely dissolve in
water, but the more resistant minerals remain
o
When a less resistant mineral dissolves, more
resistant mineral grains are released from the rock
Climate
•
The Shiprock formation in northwest New
Mexico is the central plug of resistant
lava from which the surrounding rock
weathered and eroded away.
Climate of a region strongly influences weathering
o
Determined by the temperature of a region plus the amount of
precipitation it receives
o
•
Weather averaged over a long period of time
Chemical weathering increases as…
o
Temperature increases: chemical reactions proceed more rapidly at
higher temperatures
o
Precipitation increases: more water allows more chemical reactions
•
Cold, dry climate produces lowest rate of weathering
•
The warmer a climate is, the more types of vegetation it will have and
the greater the rate of biological weathering
Resources from Weathering
•
Some resources are concentrated by weathering processes
Wet, warm climates have the most
weathering
•
In tropical climates, intense chemical weathering carries away all soluble minerals, leaving behind just
the least soluble components
Concept Check
•
What types of rocks weather most readily? What types weather least readily?
•
What climate types cause more intense weathering? What climate types cause less intense weathering?
•
How does bauxite form?