Midterm #2 Flashcards
1
Q
Cause Vs. Trigger
A
- Cause: The basic underlying geologic setting that leads to conditions conductive to rock fall. Typically, Weathering weakens unfavourably orientated rock structures over time bringing them closer to limiting equilibrium and increasing their vulnerability to triggers
- Rockslide Triggers: Processes which take naturally weakened rock masses from near equilibrium into failure. The straw that breaks the camel’s back
- Types of triggers:
1) Vibration
2) Freeze-Thaw
3) Water (rainstorms, snowmelt, man-made sources)
2
Q
Factor Safety
A
- Safety Factor = Shear Strength / Shear Stress
- If the Safety factor is less then 1, shear stress is greater than shear strength (slope is unstoppable) and the slope will fail
3
Q
Shear Strength
A
- Internal Resistance to movement
4
Q
Shear Stress
A
- Force causing movement parallel to slope, increases with slope steepness
5
Q
Fall
A
- is a free fall of bodies from steep cliffs or slopes
6
Q
Slide
A
- Is the mass of rock or soil moves as a single, coherent block
- materials slides down a pre-existing surface, such as a bedding plane, foliation surface, or joint surface
- Slump: Slow, smaller scale
- Debris Slide: fast, large scale
7
Q
Flow
A
- The solid matrix mixes as it moves, much like a viscous liquid
8
Q
Role of Water
A
- For soil that is not saturated, the surface tension of soil water pulls the soil particles together and increases the resistance to flow. As water pressure increases, this is the reverse
9
Q
Sensitive Clay
A
- In some soils the clay minerals are arranged in random fashion, with much more pore space between the individual grains
- This is often referred to as a “house of cards” structure. Often the grains are held in this position by salts precipitated in the pore space that “glue” the particles together
- As water infiltrates into the pore spaces, it can both be absorbed into the clay minerals, and can dissolve away the salts holding the “house of cards” together
10
Q
Turbidity Currents
A
- occur when Unconsolidated mud and sand slides off continental shelf
- Often triggered by earthquakes
- Can be massive in scale
- Fairly Common
11
Q
The Rissa Landslide
A
Find the answer
12
Q
The Frank Lanslide
A
Find the answere
13
Q
Stream Capacity
A
- Maximum quantity of solid material that a stream can carry
- Related to velocity (discharge)
- Higher after a rain (more sediment in water)
- Directly related to discharge
14
Q
Stream Competence
A
- Measure of the maximum size of particles the stream can transport
- Predict erosive capabilities
15
Q
Reynolds Number
A
- The Reynolds number (Re) is easily calculated and is one of the most common stream flow analysis’s used (determines laminar flow or turbulent flow)
- Re = u R / v
- u = velocity
- R = hydraulic radius
- v = kinematic viscosity
- If Re is less then 500 it is laminar flow
- If Re is between 500 and 2000 it is transitional flow
- If Re is greater than 2000 it is turbulent flow
16
Q
Hjulstrom Curve
A
- The graph shows the relationship between stream velocity and ability to transport materials
17
Q
Capacity
A
- Largest amount (weight) of debris that the river can carry
18
Q
Competence
A
- Diameter of the Largest particles (size) that can be carried
19
Q
Critical Erosion Velocity
A
- Lowest velocity at which a grain of a given size can be moved
20
Q
Setting/fall Velocity
A
Velocity falls below certain level particle fall (fall velocity) will be deposited
21
Q
Laminar Flow
A
- Streams are simply transporting or may be deposited depending upon speed of the laminar flow. They flow as a thin coherent layer, they are rare in channels
22
Q
Turbulent Flow
A
- Velocity fluctuates in all directions causing additional energy loss, most streamflow is turbulent. Initiation of turbulent flow significant increase erosion
23
Q
Velocity Distribution in a Channel
A
- Depth averaged velocity is above the bed at about 0.4 times depth
- Fastest at the middle/deepest at the surface (less friction on stream sides), increased roughness causes increased resistance
- One of the most commonly used equations governing open channel flow is known as the manning’s equation
24
Q
Thalweg
A
- Deepest part of a stream
25
Manning's Equation
- Manning's equation is an empirical equation that applies to uniform flow in open channels and is a function of the channel velocity, flow area and channel slope
- V = r s / n
- v = average flow velocity
- n = Manning roughness coefficient
- r = hydraulic radius
- s = Channel slope
26
Sediment Production and Transport
- Rainfall (sediment production)
| - Streamflow (sediment transport)
27
Dominant Discharge
- The dominant discharge is the flood that does the most geomorphological work
- Large floods have most potential to erode and transport
- Medium sized floods occur more frequently do more geomorphological work in the long-term
- Small floods cannot mobilize coarse sediment
- Most Sediment transported by floods corresponding to the bank full discharge
28
Meandering River
- Loops or meanders, forms as the stream erodes its banks
- Erosion takes place on the cut bank, which is the outside loop of the meander
- Deposition takes place on the point bar, which is on the inside loop of the meander
- Change their channel course gradually
- Create floodplain wider than the channel
- Very fertile soil
- Subjected to seasonal flooding
29
Braided River
- Many converging and diverging streams separated by gravel bars (or sand bars)
- Braided channels clog themselves with sediment, so channels always shifting
- Generally in streams near mountain fronts
- High sediment load
- Constantly changing course
30
Meandering Vs. Braided Rivers
Meandering Favoured by:
| - Low slop
31
Floodplain and Levee Formation by Suspended Load Deposition
- Boundary between channel and floodplain may be the site of a natural levee (a broad, low ridge of alluvium built along the side of a channel by debris-laden floodwater)
- Levees form when debris-laden floodwater overflows the channel and slows as it moves onto the floodplain
32
Similarities and Differences with Transport by Running Water and Wind
- Large grains are suspended in water then in air
- Saltation accounts for most sand transport in air, but is much less common in water because sand grains tend to remain in suspension in turbulent water
- Larger particles (gravel) move as bed load (traction) in water
- Air has no dissolved load
33
Wind Deposits, Loess vs. Sand Dunes
- Loess: Wind-deposited blankets of silt and clay
- Physical features are erosivity of loess soils
- Origin and distribution of Loess deposits
34
Abrasion
- Aeolian Erosion
| - Erosion baby wind-blown particles (smothered and pitted surface)
35
Deflation
- Aeolian erosion
| - Erosion of particles by wind (desert pavement)
36
Dunes
- Wind-sculpted accumulations of sand
37
Mass-Wasting Processes
- Occur on Slopes
- Down hill movement is called a landslide
- Two groups:
1) Slope Failure
2) More Continuous
38
Types of Glaciers
- Ice Cap
| - Ice sheet
39
Velocity of Ice Flow
- Glen's power flow law, rate of strain of ice depends on both shear stress and temperature
- High velocity in ice thickness, in the middle of the glacier and near the equilibrium line
- Acceleration with increasing slope or thickness
- Extending flow
40
Glacial Budgets
- Glacial ice recedes or accumulates depending on the balance of accumulation or ablation
41
Glacial Flow
- Internal Deformation (ice crystals slide past one another)
- Basal Sliding (entire glacier slides downhill on a thin film of melt water at its base)
- Glaciers always flow towards the zone of ablation
42
Cold Base Glaciers
- Frozen to the bed and velocity given by Glen's law (no basal sliding)
- Move from internal deformation
43
Warm Base Glaciers
- Melted water at their beds can facilitate sliding along the basal surface (Vb): substantial basal (and lateral edge) sliding
44
Erosion by Glaciers
- Sliding of basal ice: Ice frozen to bed cannot erode
- Debris in basal ice: Clean ice is unable to abrade solid rock. Abrasion rate will increase with debris concentration
- Ice thickness: Greater ice thickness increases vertical pressure on the debris at the base of glacier
- Relative hardness of debris and bedrock: Hard debris erodes soft rock quickly, weak debris erodes hard rock slowly
