2. Weathering
Bedrock provides the parent material for soil and
mass movement on slopes
Joints (fractures) in the bedrock provide the
location for weathering to further break apart the
rock
Joints fracture according to the properties of the bedrock
As bedrock weathers, it turns into regolith and
finer sediment
A major constituent of soil
Types of weathering
physical: dominant in dry, cool climates
Produces gravel, sand and silt sized particles of soil
chemical: dominant in wetter, warmer climates
Produces silt and clay sized soil particles
Typically operate together
3. Physical Weathering
Fragments and disintegrates rock without changing
its chemical composition
Types of physical weathering
Frost Action
moisture in rock joints freeze and expand
expansion forces rock apart
Crystallization
Evaporation of water in rock joints deposits salt crystals
Accumulation of crystals exerts an outward pressure in the joint,
forces rock apart
Hydration
Some minerals in rocks are capable of absorbing water
Gypsum: CaSO4·H2O
Hydration of crystals cause them to expand, forcing rock apart
Pressure-release jointing (exfoliation)
Erosion of sedimentary layers over igneous intrusions removes
weight, and outer layers of igneous rock break off in sheets
9. Chemical Weathering
Water alters the chemical properties of the rock
through decomposition and decay
Four types of chemical weathering
Spheroidal weathering
Water penetrates joints and fractures
dissolves cementing materials
rounds edges of the rock
Hydrolysis
Water reacts with minerals in the rock, creating new minerals
Causes the crystal structure in the rock to fail
Oxidation
The oxygen in the water reacts with rock minerals to create varies oxides
Oxides are bonded more weakly to the rock and erode away more easily
Carbonation and solution
Carbon dioxide dissolves in water vapor to form carbonic acid
Carbonic acid in precipitation dissolves limestone (CaCO3)
