Surface Processes

Question 1

mass wasting

Answer 1

downslope movement of rock and debris under the influence of gravity

Question 2

landslide

Answer 2

general term for all types of mass movement

Question 3

causes of slope failure

Answer 3

• contributing factors that make slope vulnerable to failure
• Main cause: gravity
• Others: slope angle, local relief, thickness of soil over bedrock, orientation of planes of weakness in bedrock, climatic factors (ie. Ice, water in soil, precipitation), vegetation

Question 4

triggers of slope failure

Answer 4

• single event that initiates movement
• Earthquakes
• Weight added to upper part of slope
• Undercutting bottom of slope
• Heavy rainfall
• Volcanic activity
• Human modification

Question 5

relationship between gravity and slope stability

Answer 5

• Understanding the materials involved and forces involved is key to predicting slope stability
• Shear stress < shear resistance = stable (frictional force on block is sufficient that it won’t fall -> Even with a high slope angle, with enough friction the slope may still be stable)
• Shear stress > shear resistance = unstable, will fall
• Shear stress < shear strength of solid -> stable (In unconsolidated materials like soil, we consider the strength of the material (shear strength))

Question 6

angle of repose

Answer 6

• Loose materials rest at a natural angle of repose, which is different depending on the material
• If angle > greater than their angle of repose -> unstable

Question 7

effect of rock structure on slope stability

Answer 7

• Parallel cracks/bedding/fractures on granite rocks are planes of weakness
• Low porosity rocks in a sequence can prevent groundwater from seeping away – another plane of weakness

Question 8

effect of water on slope stability

Answer 8

• Unsaturated soil or debris vs. Saturated soil or debris
• Surface tension is an important force – a little bit of water is okay, but if material is saturated, the grains are forced apart and the material flows

Question 9

how are slope features classified?

Answer 9

• Combines type of movement, rate of movement, type of material
• Slides, flows, falls

Question 10

slides

Answer 10

• Failure plane along a definite slip surface – mass stays intact
• Transactional (glide block)
• Rotational (slump)

Question 11

flows

Answer 11

• Material moves as viscous fluid
• Debris flows: earth or mud
• Debris avalanche
• Slump earth flow complex: In thick soils and soft sedimentary rocks; common for slump to break up into smaller blocks as it travels down slope and begin to flow
• Lahar: volcanic mud/debris flow
• Creep: a imperceptibly slow type of flow

Question 12

falls

Answer 12

• Mass falls through the air

- ex. Rock fall

Question 13

how do we decrease slope hazards?

Answer 13

• Identify unstable and potentially unstable slopes by geological mapping
• Legislate appropriate zoning laws and enforce them
• Control or stop existing landslides
• Design slopes or engineer structures to prevent new landslides

Question 14

techniques used to stabilize landslides

Answer 14

• Build retaining walls, sink piers into stable ground (need to remember to increase surface or subsurface drainage -> give water a way to drain freely out of walls otherwise pressure will build and it’ll collapse)
• Revegetate slopes (Hyrdoseeding, applying jute netting)
• Regrade slopes (cut problematic parts off)
• Cover slopes (Chicken wire “shotcrete”; rock bolts -> steel bolts anchored in cement to connect outer rock to a more stable layer in the middle)
• Contain/redirect the hazard (Ex. Avalanche sheds)