NAME: _______________________
DATE: _______________________
“MECHANICAL & CHEMICAL WEATHERING”
Student Organizer
Weathering Overview:
1. Describe how different climates can have different effects on the type of weathering that
occurs.
Hot and wet climates enhance chemical weathering and cold, wet climates enhance
physical/mechanical weathering. Weathering is slower in dry regions regardless of
temperature.
Mechanical Weathering Overview:
2. Why does water freeze downward into the fractures of rock?
The water at the surface freezing first due to the immediate exposure of freezing temperatures.
The ice cannot expand upward because the surface is already a frozen solid, therefore, the
water freezes downward into the rock. As the water freezes and expands causing the rock to
break.
a. Where type of climate does Frost Wedging most likely to occur, and why?
Ice wedging occurs in cold and wet climates where the freeze/thaw cycle takes place.
For example, mountain ranges with high altitudes are prone to ice wedging due to the
temperature changes.
3. Describe the weathering process of Exfoliation? Why do rocks break off into layers?
Exfoliation is the process in which rocks weather by peeling off in sheets rather than eroding
grain by grain. As a rock face erodes, rocks underneath have less weight and pressure on
them, and thus they expand breaking the rock off in layers parallel to the rock.
a. Where is exfoliation most likely to occur?
Exfoliation occurs mostly in mountain regions where intrusive igneous rock has been
uplifted and exposed by erosion.
4. What is the force behind weathering by Thermal Expansion and Contraction?
Heat causes the crystals in the rocks to expand and contract loosen the grains of the rock to
cause them to break apart.
a. Where is it most likely to occur?
Thermal expansion and contraction is most likely to occur in desert regions where
temperature varies daily.
5. What causes weathering by Crystal Growth?
When salt water seeps into the grains of rock and the water evaporates, it leaves the salt to
crystalize pushing the grains apart. Similar to ice wedging, expect the water evaporates and
the salt is causing the rocks to break apart.
a. Where is it most likely to occur?
Crystal growth occurs in coastal region and desert regions where there is enough salty
water.
NAME: _______________________
DATE: _______________________
6. Explain the force behind weathering by Tree Roots.
Tree roots penetrate into the fracture of rocks and as they grow, they apply pressure on the
rock, causing the fractures to expand and breaking the rock.
a. Where is it most likely to occur?
Tree roots growth occurs in regions with a warm, moist climate to support dense forests.
7. Explain the force and process behind weathering by Abrasion?
Abrasion occurs when rocks are broken and worn down by the direct contact of other rocks.
Nearly all types of erosion provide an opportunity for abrasion to occur.
a. Where is it most likely to occur?
Abrasion occurs in areas with the harshest environments.
b. What else do you think might abrade rock besides sediments?
Glaciers in cold and wet climates, steep terrains in dry regions.
Chemical Weathering Overview:
8. How is chemical weathering different from mechanical?
Chemical weathering breaks down the chemical composition of rocks one atom at a time.
a. What are the three categories of chemical weathering?
Dissolution, oxidation, and hydrolysis
9. Dissolution occurs when water contains acids come in contact with soluble rock dissolving
away rock little by little. Describe how the rocks in caves are produced by this process.
Caves are formed when the calcite mineral in limestone get dissolved by groundwater that
contains dissolved carbon dioxide (weak acid).
10. Oxidation occurs when rocks react with oxygen to create rust. What is the most common
element found in rocks that this type of chemical weathering occurs with?
Iron; occurs mostly in moist regions and more rapidly in warm climates.
11. Hydrolysis is a process in which chemical weathering occurs due to the direct reaction of
water molecules. Water molecules take the place of other ions in a mineral to create a new
mineral. Explain how hydrolysis effects feldspar.
Among the most important products of hydrolysis are the clay minerals. Clays are flat, hydrous
minerals in the mica family that form by the hydrolysis weathering of feldspar. Humid
environments are more prone to hydrolysis than arid regions. Thus hot, humid areas such as
tropical rain forests are ideal for hydrolysis reactions.