Earth Science- Mass Movements
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- What does gravity cause?
- The downward movement of landslides and subsiding ground.
- What are some external causes of slope failure?
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1) Steepeing the slope by faults or fault movements.
2) Removing support from low on the slope.
3) Adding mass high on the slope as in sediment deposition. - What is the cause of a landslide?
- Loading the head and reducing the toe.
- What is an internal cause of slope failure?
- Inherently weak materials such as clay.
- Whats the problem with clay?
- It is too small, and too thin and weathers easily under low pressure and low temperature.
- Where is most feldspar found and how is it formed?
- Found in granite and is formed under high pressure and temperature.
- How does unloading occur?
- Clay breaks off through weathering and pressure is removed.
- What does the mechanical stregnth of rock depend on?
- 10-15% of the rock with the smallest grain size.
- What is another internal cause of slope failure?
- Decrease in cohesion
- What are some roles of water?
- It is absorbed and adsorbed by clay materials. Since it is polar it can be effected electrostatically.
- How does water cause slope failure?
- Water can dissolve some of the minerals that bind rocks as well as eroding loos materials.
- How does water weaken earth materials?
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1) Decreasing cohesion
2) Subsurface erosion
3) Creating pressure in pore spaces.
4) Weight
5) Interplay of clay materials - What is the final internal cause of slope failure?
- Adverse geologic structures.
- What triggers mass movements?
- Heavy rains, Earthquakes, Thawing frozen ground, construction projects of humans.
- What is the slowest but most widespread type of mass movement?
- Creep
- What is creep and where are its effects most noticible?
- Movement of soil and upper most bedrock, its effects are most noticible on trees and fences.
- How does rock and soil move by creep?
- Expansion and contraction, the soils swell and then shrinks
- Why is the contraction occuring?
- Because of the pull of gravity
- What is the shrinking caused by?
- The soil thawing, drying, cooling and gravity pulling.
- What is a fall?
- Elevated rock masses seperate along joints, bedding or other weaknesses.
- What are the main causes of a fall and how does it ususally occur.
- Gravity, earthquakes and people, occurs extremely rapidly and under dry conditions.
- What are slides? What is the main cause of them.
- Movements above one or more failure surfaces. Gravity is the main cause.
- What is a rotational slide and how does it typically occur?
- Slump is a roational slide in which the head moves down and typically backwards.
- What are transitional slides?
- Masses that move down and out by sliding on surfaces of weakness.
- What are the three outcomes of transitional slides?
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1) They remain basically coherent.
2) They may deform and disintegrate.
3) They may spread laterally when the underlying material fails and flows.q - How do flows behave and what are some different types of them?
- They move like fluids, names for them are Loess flow, earthflow, mudflow, debris avalanche, lahars.
- In what ways do avalanches move?
- Creep, fall, slide and flow
- How do avalanches occur?
- From triggers such as earthquakes or people, accumulation high on the slopes loads the head and sets the stage for failure.
- What is the top speed for an avalanche?
- 230 mph
- What is subsidence?
- The ground moves down and either sags gently or drops catastrophically as voids.
- What material often involved with subsidence causes the collagpse of roads built on top?
- Limestone
- What in rock helps support the weight of overlying rock?
- Fluids
- What happens when water or oil are squeezed or pumped out of pores in rock or grains?
- The pore pressure casues the grains to move together and they are compacted.