Mass wasting Flashcards
Downslope movement of the rock and regolith near the earth’s surface
Mass Wasting process
True or False. Integral part of the erosional process, as it move material from higher elevations to lower elevations.
True
Any perceptible downslope movement of the rock or regolith is often referred to in general terms as a __________.
Landslide
When Cherry Hills landslide happened?
August 1-3, 1999
What type of mass movement happened in Cherry Hills Landslide?
Complex landslide. Started out as a slump and developed into a debris flow near the base.
What type of mass movement happened in the Guinsaugon, Leyte?
Complex landslide (rock and debris avalanches)
When Guinsaugon landslide happened?
February 17, 2006
What type of mass movement happened in Andap, New Bataan?
Debris flow
When Andap Debris flow happened?
December 04, 2012
What is the maximum runup height of Andap Debris Flow?
1.8 meters
The material that is (practically) still in place and adjacent to the highest parts of the main scarp.
Crown
A steep surface on the undisturbed ground at the upper edge of the landslide is caused by the movement of the displaced material away from the undisturbed ground. It is the visible part of the surface of the rupture.
Main scarp
The highest point of contact between the displaced material and the main scarp.
Top
The upper parts of the landslide along the contact between the displaced material and the main scarp.
Head
A steep surface on the displaced material of the landslide is produced by differential movements within the displaced material.
Minor scarp
The part of the displaced material of the landslide that overlies the surface of rupture between the main scarp and the toe of the surface of rupture.
Main body
The portion of the landslide that has moved beyond the toe of the surface of rupture and overlies the original ground surface.
Foot
The point of the toe farthest from the top of the landslide.
Tip
The lower, usually curved margin of the displaced material of a landslide, it is the most distant from the main scarp.
Toe
The surface that forms (or has formed) the lower boundary of the displaced material below the original ground surface.
Surface of rupture
The intersection (usually buried) between the lower part of the surface of rupture of a landslide and the original ground surface.
Toe of surface of rupture
The part of the original ground surface overlain by the foot of the landslide.
Surface of separation
Material displaced from its original position on the slope by movement in the landslide. It forms both the depleted mass and the accumulation.
Displaced material
The area of the landslide within which the displaced material lies below the original ground surface.
Zone of depletion
The area of the landslide within which the displaced material lies above the original ground surface.
Zone of accumulation
The volume bounded by the main scarp, the depleted mass and the original ground surface.
Depletion
The volume of the displaced material that overlies the rupture surface but underlies the original ground surface.
Depleted mass
The volume of displaced material that lies above the original ground surface.
Accumulation
The undisplaced material is adjacent to the sides of the rupture surface. Compass directions are preferable in describing the flanks but if left and right are used, they refer to the flanks as viewed from the crown.
Flank
The surface of the slope that existed before the landslide took place.
Original ground surface
Currently moving
Active
Moved within the last 12 months but not active at present.
Suspended
Inactive landslide that has been activated again.
Reactivated
Has not moved within the last 12 months.
Inactive
4 classification of inactive
Dormant
Abandoned
Stabilized
Relict
Inactive but can be reactivated by its original cause or other causes.
Dormant
Inactive landslide which is no longer affected by its original cause.
Abandoned
Inactive but has been protected from its remedial measures.
Stabilized
Inactive which developed under climatic or geomorphical conditions.
Relict
Different types of movement.
flow, slide, slump
Type of material involved
rock, debris, earth, and mud
Relative proportions of _______ and _______.
material and water
Velocity of movement
Slow and rapid
Thickness
shallow and deep seated
type of triggering factor
rain-induced and earthquake induced
Types and Forms of Mass Movement
Fall
Topple
Slide (rotational and translational)
Flows
Lateral Spread
Creep
Complex
A detachment of soil or rock from a steep slope and the more or less free and extremely rapid descent of the material.
Fall
A failure in the support conditions of bedrock. It is also a forward rotation of the slope of a mass.
Topple
True or False. Fall can have a bouncing and rolling movement.
True
Falls can be triggered by __________ and _________.
lateral pressure (roots, crystallization pressure, ice wedging, etc.)
lost by underlying support (erosion on cliffs)
True or False. Toppling mostly occurs in combination with falls.
True
Moving slab of soil or bedrock that moves downslope as a whole, remaining in contact with the underlying material.
Slide
Have a more or less circular failure surface. In general a steep, almost vertical headscarp (crown), with the slided mass in front of it. It makes that the slide mass (body) is backtilting towards the headscarp . Tensional cracks can occur in combination with small steps on the body.
Rotational slide
The sliding mass moves along a pre-existing failure plane (e.g. bedding, schistosity , joint, discontinuity between slope debris and the underlying rock). The total displacement along this failure plane is generally longer.
Translational slide
Types of translational slide
Soil slips (sheet and slab slide)
Rock slide (planar, stepped, wedge)
Debris slide
Shallow translational movement in soil material.
Soil slips
In cohesionless and dry soils.
Sheet slide
Movement takes place along one and the same failure plane.
Planar slide
Movement occurs along a number of parallel failure planes.
Stepped slides
Failure is controlled by two planes which define a wedge shaped block, which is loosened from the rock slope.
Wedge failures
Movements occurring on steeper slopes (25º- 35º), where the slope debris slides off along the discontinuity with the underlying weathered rock.
Debris slide
Great internal deformation inter-granular movements dominate over shear surface movements. The internal vertical velocity distribution is not uniform, but the material near the surface runs at a higher velocity rate than the underlying material
Flow
Types of flow
earth flow, mudflow, debris flow
A type of slow movement, in which the rate of internal deformation is limited. This type includes solifluction The general form of faster earthflows is that material slumps away from the top, leaving a steplike terrace bounded by a curved, wall like scarp The saturated material flows sluggishly to form a bulging toe
earthflow
A type of a fast moving flow The material is (over)saturated with water. It mostly originates from overland flow in heavy rainfall, dragging soil particles with it The kinetic energy can build up so high that and even stones can be taken along.
mudflow
From falls and high energy slides can also behave as a flow especially if air or water is entrained in the initial movement. The trapped
fluid may develop high pore pressures, which buoy up the individual debris particles Alternatively, the numerous interparticle impacts may produce an effect analogous to intermolecular motion in a real fluid, thus enabling even dry, non cohesive, debris to flow. This type of movement is also called block
flow, if taking place in larger material
Debris flow
Define spread as an extension of a cohesive soil or rock mass combined with a general subsidence of the broken mass of cohesive material into softer underlying material
Lateral spread
True or False. Spreads may result from liquefaction or flow (and extrusion) of the softer material.
True
The slow movement of soil or bedrock down slope. It occurs where the stresses on the slope material are too small to create a rapid failure, or as a result of thawing/freezing effects.
Creep
Can be classified those slope movements whereby at least two different types of landslides together are responsible for the occurrence or continuation of the slope movement in the area
Complex
Geological causes of mass movement
- Weak material
- Sensitive material
- Weathered material
- Sheared material
- Jointed or fissured material
- Adversely oriented mass discontinuity (bedding, schistosity, etc.)
- Adversely oriented structural discontinuity (fault, unconformity etc.)
- Contrast in permeability
- Contrast in stiffness (stiff, dense material over plastic material)
Morphological causes of mass movement
- Tectonic or volcanic uplift
- Glacial rebound
- Erosion of slope toe
- Erosion of lateral margins
- Subterranean erosion (solution, piping)
- Deposition of load on the slope or its crest
- Vegetation removal
Physical causes of mass movement
- Intense rainfall/ Prolonged exceptional precipitation
- Rapid snow melt/ Thawing/ Freeze and thaw weathering
- Earthquake/ Volcanic eruption
Human causes of mass movement
- Excavation of the slope or its toe
- Deposition of load on the slope or its crest
- Drawdown (of reservoirs)
- Deforestation
- Irrigation
- Mining
- Artificial vibration
- Water leakage from utilities
The sequence of a _________ and _________ part off the slope is associated with landslide niches and associated deposits.
Concave and convex
__________ is related to retrogressive sliding.
Step-like morphology
____________ are associated with the head part of a slide with the outcrop of failure plane.
Semicircular niches
_____________________ indicates a rotational movement of slide blocks. This feature appears oval or elongated depressions with imperfect drainage conditions.
Back tilting of slope faces
Irregular slope morphology. Micro-relied associated with shallow movements or small retrogressive slide blocks.
Hummocky relief
____________ indicates a recent event. Its formation occurs with sliding and toppling movement.
Formation of cracks
___________ can indicate a presence of a landslide scar.
Steepening of slopes
How many degrees is angle repose
35
True or false. Homogenous rocks are stable cliff
True
