1 Mass Wasting Today: • Definition • Factors Influencing Mass Wasting • Classification & Examples Be certain to read Ch 13 in your book - I am curtailing it here Slide at La Conchita CA Definition of Mass Wasting • Down slope displacement of soil and rock under direct influence of gravity – Rapid (e.g., avalanche) – Slow (e.g., creep) • Result: – Landscape evolution – Hazard
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
Mass WastingToday:• Definition• Factors Influencing
Mass Wasting• Classification &
Examples
Be certain to read Ch13 in your book - Iam curtailing it here
Slide at La Conchita CA
Definition of Mass Wasting
• Down slopedisplacement of soiland rock under directinfluence of gravity– Rapid (e.g., avalanche)– Slow (e.g., creep)
• Result:– Landscape evolution– Hazard
2
Landscape evolution:
• Mass wasting one of main processes of sediment transport• Results in change in shape of slopes (hills, cliffs, mountains, river
banks etc.)• Other processes that move sediment and shape landscape Rivers,
Glaciers, Wave, Wind
Simple model for MW
• MW occurs when– force of gravity
exceeds stabilizingforces
– Friction, cohesion &strength
• Consider block oninclined plane...
Normal
Gravity
Down slope
Stabilizing
If Down slope force > Stabilizing force then...
3
Factors influencing Mass Wasting: Slope
• Increase Slope– Increase down slope forces– Movement occurs when down-slope forces exceed
stabilizing forces• Rives and waves cut steep cliffs. (so does man)
Factors influencing mass wasting: Water• Loading:
– Add water = add mass– Increases down slope forces
• Lubrication:– Decrease friction
• Cohesion– Add water and increase
cohesion due to surfacetension (e.g. sand castles)
– Too much water decreasescohesion when sedimentgrains no longer touch (e.g.wet sand castle falls).
4
Factors influencing mass wasting:• Deforestation
– Root systems bind soil– Remove it, and cohesion
decreases
• Earthquakes– Ground shaking can
trigger mass wasting
Types of Mass WastingFalls Slides Flows
Be certain to read about this inChapter 13 - I am skipping it here.
5
Creep is a type of flow caused by frost heave orclay expansion
• Volumetrically the most significantform of mass wasting.
6
Examples of Creep
Vaiont Italy, 1963• Bedrock dips into canyon• Reservoir filled, water
wicked up bedding(lubrication)
• 240 x 106 m3• 90 m wave• 7 minutes 2600 dead
7
Debris Flow at Mt. Huascaran, Peru
• Before 1970:• Village of Yungay, Peru• Off - shore EQ (benioff)
M~7
• After event:• Slide block of ice and rock
(>2.2 x 106 m3)• Debris flow > 9 km
distance• > 100 mph• >20,000 killed
Related Documents
