Download Sedimentation

SOILS, WEATHERING, AND
EROSION
Where the geosphere and the biosphere meet
Learning Targets
1. Define mechanical and chemical weathering
2. Discuss agents of weathering
3. Give examples of each type of weathering
Soil Forming Processes
1. Weathering: process that changes solid rock
into sediments
2. Erosion: process that moves sediments
3. Sedimentation: depositing of rock pieces
Weathering
Erosion
Sedimentation
Weathering
1. Large rocks and mountains  sediment
2. Sediment sizes
a)
b)
c)
d)
e)
Boulders
Gravel
Sand
Silt
Clay
3. What processes act on weathered sediments?
a) Erosion (movement)
b) Sedimentation (deposition)
Weathering
1. Weathering only happens at the surface
2. Occurs in 2 forms:
a) Mechanical: change in shape or size
 Also
known as physical weathering
b) Chemical: change in composition
Mechanical Weathering (Physical Weathering)
Chemical weathering
Mechanical Weathering (Physical Weathering)
1. 3 main types:
a) Ice wedging
 Cycles
of freezing and thawing
b) Abrasion
 Physical
contact and friction
c) Biological weathering
 Roots,
burrowing animals, fungi, lichens, humans
Ice wedging
Abrasion
Biological weathering
Mechanical Weathering
1. Increases surface area
2. Increased surface area leads to quicker
weathering. Why?
a) More rock is exposed to the atmosphere; less
rock is protected from water and oxygen
Increasing surface area
Chemical weathering
1. Creates new minerals or compounds
a) Different composition not just different size
2. Different minerals are stable at surface than
at depth
3. Mainly caused by
a) Water: dissolves minerals
b) Oxygen: combines to form oxides
c) Carbon Dioxide: makes water acidic
Oxidation
Hydrated obsidian
Oxidized ultramafic rock
Rust: chemical weathering of Iron
Chemical Weathering
1. Some organisms release chemicals that
break down rocks and minerals
2. Fungi and bacteria are very important
parts of chemical weathering
Lichens colonizing a lava flow
Differential weathering
1. Weather rates speed up based on
a) Rock and Mineral Type
 Sedimentary
rocks weather fastest
b) Climate type
 Temperature
increases: Chemical reactions more
rapid
 Precipitation increases: More water allows more
chemical reactions