Lecture 10+11: Mass Movements Flashcards
1
Q
driving force, resisting force and mass movement
A
- when driving force > resisting force, mass movements occur
- the driving force is the component of gravity parallel to the slope
- resisting force is proportional to inertia and friction and counteracts the driving force
2
Q
conditions decreasing stability (external)
A
- adding mass high on a slope (external role of water: rain erodes material)
- steepening of slope (less steep = more stable)
- removing support at the base of the slope (less support = less stable)
- removal of lateral support decreases stability (example of a rotational slide; more unstable)
3
Q
decreasing stability through presence of weak material
A
- lubricants like clay
- material that deforms practically under stress and loses strength
- crumbly poor consolidated material
4
Q
friction decreasing stability
A
- controlling factors: surface roughness of the surfaces; presence of lubricants
- friction coefficient
5
Q
fractures in rock decreasing stability
A
- rock fractures naturally in parallel planes of weakness
- more stable fractures = perpendicular to the slope
- less stable fractures = parallel to the slope
- regional scale; local scale; hand sample scale; microscopic scale
6
Q
internal roles of water on internal stability
A
- adding weight to porous earth materials
- dissolving cement binding minerals together
- liquefaction: low pore pressure - strong binding force; high pore pressure - weak binding force
- congelifraction: disintegration of a rock due to several cycles of water freezing and melting
7
Q
geochemistry of the crust
A
- structures of silicon and oxygen
- basic building block is the silicon-oxygen tetrahedron molecule
- four oxygen ions surrounding a much smaller silicon ion
8
Q
Silicates and clay
A
- silicates: group of minerals containing Si and O combine with other elements
- Clay: general term which describe a variety of complex sheet silicates
- structures is a stack of think sheets
- swelling clays: group of clays which tend to swell when exposed to water, results in loss of strength
9
Q
sensitive clays
A
- clays that can change internal structure almost instantaneously
- stable conditions can become unstable without warning
10
Q
flocculated structure
A
- stiff and strong
- salt bind the clay sheets and slit together
11
Q
dispersed structure
A
- soft and weak behaves almost like a fluid
12
Q
three types of rocks and their structure
A
- igneous rocks form by cooling and solidification from a molten liquid called magma
- sedimentary rocks form by the erosion and compaction of rock fragments or by precipitation
- metamorphic rocks form by the alteration of existing rocks by head and or pressure
13
Q
triggers of mass movements
A
- natural causes: earthquakes; volcanoes; erosion; water
- human causes: construction; tunneling
14
Q
falls
A
- rapid free fall mass movement
- fragment size form grain to large blocks
15
Q
slides (planar surface and curved surfaces)
A
- mass movement involving motion along a failure surface
- material remain as a block
- Planar surface = translational slide
- curved surface = rotational slide
