Download Mass movement - St Angela`s College Geography

The earth’s surface – shaping the crust.
Weathered material moves down slope under the influence of gravity. This movement can be either slow (as in soil
creep) or rapid (as in landslides)
Settings
Local slopes
Coast cliff
Bogbursts (honours only)
Major world catastrophe (honours only)
Mass movement
Regolith: Loose material weathered from the earth’s surface.
Mass movement: The down slope movement of weathered material due to the pull of gravity.
Factors which affect mass movement
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High water content causes landslides and mudflows.
Vegetation such as trees reduces mass movement.
Steep slopes aid fast mass movement.
Man’s interference may aid or restrict mass movement
Removal of trees on steep slopes and road building aid mass movement.
Planting trees on slopes restricts mass movement.
Types of mass movement
Avalanches: Very rapid down slope movement of snow or ice in a mountain slide.
Landslide: Rapid down slope movement of loose soil and rock
- Due to a road cutting into a steep slope which may cause regolith above the road to become
unstable and fall down slope.
- Constant erosion by waves causing undercutting of cliffs. Overhanging ledges collapse
downwards as a landslide.
Earthflows and mudslides: This is slow to rapid mass movement. These occur when soil and water become
saturated with water on steep slopes. This water may result from heavy rain or snowmelt after a volcanic eruption.
Example: Columbia – 20,000 killed as a result of a mudflow.
Bogbursts: Rapid mass movement, these occur in mountain bogs after periods of heavy rain. Saturated peat
moves quickly down slope.
Soil creep: Slow mass movement, large amounts of regolith moves slowly down slope.
Evidence of mass movement
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In places where rapid mass movement occurs a scar remains where the regolith fell down slope. A mound of
debris is found at the base.
Slow mass movement often causes bending of tree trunks, ESB poles tilting, bulging or bust walls at the end of
slopes.
Terracettes (like steps) appear on steep grassy slopes in fields.
Major world catastrophe – mass movement
20,000 buried alive in Columbia. The snowcapped Nevado del Ruiz mountain erupted after being dormant for 140
years. The hot volcanic ash from the eruptions mixed with and instantly melted the thick mountain snows. This
created a vast river of mud, which surged down the mountainside, devastating the town of Armero at the foot of the
mountain.
A crashing sea of mud washed many of the town’s buildings away. It is estimated that 20,000 people were buried
under the torrent of mud that came with a horrible noise. It dragged away houses cattle, trees, even gigantic rocks.
Colombia is a country in South America.
Read the information above carefully. For each heading you should look up your book and the diagrams for each
feature. If you are unsure of the diagrams you need to draw them onto this revision sheet.
When you have studied the information see if you can answer the questions below. Remember the format:
STATEMENT – DEVELOPMENT – EXAMPLE
Questions:
1. What are the two main types of mass movement. Give one example of each.
2. List and explain three factors which effect mass movement.
3. What evidence would you see on the landscape after a landslide.
4. What evidence on the landscape would prove soil creep was occurring.
5. Write an account of one major world catastrophe which has occurred due to mass movement.
Now go to studyclix.ie. Select Junior cert geography, then higher level, finally the section on mass movement.
Attempt each question then check your answers. If you come across a question you can't do, ask in class.