Shaping the Earth’s Crust
Weathering and Erosion
Shaping the Earth’s Crust
• The rocks and soil of the earth’s crust are
continually being worn down because of a
number of processes.
• These processes are known collectively as
Denudation.
• Denudation occurs as a result of both
weathering and erosion.
Denudation
•
Denudation is caused by both weathering and erosion.
Denudation
Weathering
1.
2.
Mechanical Weathering
Chemical Weathering
Erosion
1. Moving water (rivers/sea)
2. Moving Ice (glaciers)
3. Moving Air (wind).
Weathering and Erosion
Weathering
•
Weathering means the breakdown of rocks that are exposed to the weather.
•
There are two types of weathering, Mechanical Weathering and Chemical
Weathering
Erosion
•
Erosion means the breakdown of rocks and the removal of their particles.
•
Erosion is caused by moving air (wind), moving water (rivers/sea), and
moving ice (glaciers).
Mechanical Weathering
• Mechanical weathering breaks up the rocks into smaller
pieces.
• One type of mechanical weathering is called Freezethaw action.
• Freeze-thaw action breaks the rock into smaller pieces.
• It occurs high in the mountains where there is lots of rain
and the temperature rises above and below 0 degrees
Celsius quite often.
Freeze-Thaw Action
Chemical Weathering
• Chemical weathering dissolves rocks.
• One example of chemical weathering is called Carbonation.
• Carbonation occurs in limestone landscapes, where bare limestone
rock is exposed to the rain.
• It occurs because rainwater mixes with carbon dioxide in the
atmosphere, forming a weak carbonic acid.
• This acid reacts with calcium carbonate in the limestone, causing
the rock to slowly dissolve.
Carbonation – Karst Landscapes
• Carbonation occurs in areas where bare limestone rock
is exposed to the weather.
• These areas are known as karst landscapes, after a
limestone region called Karst in Slovenia.
• An example of a Karst landscape in Ireland is the Burren
in Co. Clare.
• Here the soil has been worn away, leaving the bare
limestone rock exposed. Carbonation has created many
spectacular features, particularly underground.
A Karst Limestone Pavement
Mass Movement
• Mass movement means the movement of any loose
material (rocks, soil, mud) down slope under the
influence of gravity.
• The loose material is known as regolith.
• The rate of mass movement is influenced by 4 factors.
•
•
•
•
Gradient
Water Content
Human Activity
Vegetation
Influences on Mass Movement
• Gradient – Mass movement occurs on sloping land. Mass
movement is fastest on steep slopes.
• Water Content – After heavy rain the regolith (loose material) is
heavier.
• Human Activity – People often cut into hillsides to make roads or
railway lines. This creates steep slopes where mass movement can
occur.
• Vegetation – The roots of trees and plants help keep the regolith
together, slowing down mass movement.
Types of Mass Movement
•
There are different types of mass movement. They are grouped according
to the speed at which they occur.
Types of Mass Movement
Speed – Slow
Speed – Fast
1. Soil Creep
1. Landslides
2. Bog bursts
3. Mudflows
Soil Creep
Soil Creep
Landslides
Mudflows