Dynamic Surface L7 Flashcards
What is a scree?
Particles weathering off an outcrop and dropping down due to gravity
What are 4 types of mass transports due to gravity?
Falls
Slides
Slumps
Debris flow
What is a rock slide?
A coherent unit falls down a slope under gravity
What is a rock slump?
Sediment that is not well lithified undergoes internal deformation usually as a result of over saturation of sediment on the slope.
What is a debris flow?
Occur when a high density viscous liquid flows down a slope picking up larger particles of rock than an average river
What are the 4 types of fluids that enable mass transport?
Air
Ice
Dense sediment and water mixtures
Water
What is the Reynolds Number equation?
Re = u*l / v
where u = velocity of flow
v = fluid viscosity
l = depth
What is laminar flow?
At all points in laminar flow all molecules are moving downstream
What is turbulent flow?
At any point in turbulent flow, a molecule may be moving in any direction, but the net flow is downstream
Would the Reynolds Number (Re) be high or low during laminar flow and hence will velocity and viscosity be high or low?
Low Re
Low velocity
High viscosity
Would the Reynolds Number (Re) be high or low during turbulent flow and hence will velocity and viscosity be high or low?
High Re
High velocity
Low viscosity
What fluids exhibit turbulent flow and is viscosity high or low?
Water and air exhibit turbulent flow with a low viscosity
What fluids exhibit laminar flow and is viscosity high or low?
Ice and dense sediment and water mixtures exhibit laminar flow with a high viscosity
What is bedload transport?
The transport of grains in which the grains retain some contact with the sediment bed as they move downstream
What is suspended load/suspension?
The transport of grains in which they never touch the sediment bed as they move downstream
What are the 2 types of bedload transport?
Rolling/traction
Saltation
What is rolling/traction?
Grains roll along the top of the sediment bed in a slow moving flow.
What is saltation?
Grains bounce along the sediment bed continuously in a fast moving flow.
What is the Hjulstrom diagram?
A graph that shows the relationship between sediment size and velocity, which dictates how the sediment will be transported, or if it will be eroded/deposited
What is the Froude Number equation?
F = u / √g*h
where u = velocity of flow
g = acceleration due to gravity
h = depth of flow
What must the value of the Froude Number be to indicate a lower flow regime?
F < 1
What must the value of the Froude Number be to indicate a upper flow regime?
F > 1
What does a Froude Number value of F > 1 indicate?
Upper flow regime
What does a Froude Number value of F < 1 indicate?
Lower flow regime
What are the 2 types of grain size variations in a single bed?
Normal grading
Reverse grading
What are the 2 types of grain size variations in a series of beds?
Fining-up
Coarsening-up
What is normal grading?
Grain size gets progressively larger as you move further down in the bed
What does normal grading/fining-up reflect?
Gradually reducing flow velocity meaning the flow does not have the energy to carry larger grain sizes so grains get progressively smaller over time.
What does reverse grading/coarsening-up reflect?
Gradually increasing flow velocity meaning the flow gains the energy to carry larger grains sizes so grains get progressively larger over time.
What is the bedform stability diagram?
A graph that shows the stability of different types of sedimentary beds based on the relationship between flow velocity and grain size.
What type of bedding are part of the lower flow regime?
Ripples
Subaqueous dunes
Lower flat beds
What type of bedding are part of the upper flow regime?
Antidunes
Upper flat beds
How does ripple cross strata form?
1) Grains of sand move up the upstream side of the ripple
2) Grains of sand that reach the crest of the ripple avalanche down the downstream side of the ripple
3) This repeated process causes the ripple to advance downstream as sediment is removed from the upstream side and deposited on the downstream side
What is the name of the upstream side of a ripple?
Stoss
What is the name of the downstream side of a ripple?
Lee
What does an asymmetrical ripple indicate and where are these found?
Dominate flow in a downstream direction
Common in rivers
What does a symmetrical ripple indicate and where are these found?
Oscillating flow (flow goes back and forth)
Common in lakes
What is the height of a ripple?
The distance from trough point to summit point
What is the wavelength of a ripple?
The distance from one trough point to the next trough point
What is the ripple index?
Wavelength / height
What are the 6 types of ripple crests in plan view?
Straight crested
Sinuous
Catenary
Lunate
Linguoid
Wave-formed ripples
What is the progression of ripple crests from low velocity to high velocity?
1) Straight crested
2) Sinuous
3) Catenary
4) Lunate
5) Linguoid
What does a straight crested cripple look like?
Parallel lines perpendicular to direction of flow
What does a sinuous ripple crest look like?
Gently curving lines perpendicular to direction of flow
What does a catenary ripple crest look like?
Catenary ripple crests look like how I used to draw waves in the sea
What does a lunate ripple crest look like?
A horseshoe with the open end facing downstream of the direction of flow
What does a linguoid ripple crest look like?
A horseshoe with the open end facing upstream of the direction of flow
What type of bedding will straight crested ripples produce?
Planar cross-bedding
When looking at planar cross bedding perpendicular to the direction of flow, what will you see?
Planar cross-bedding (parallel lines angled upwards in the opposite direction of flow)
When looking at planar cross bedding parallel to the direction of flow, what will you see?
Planar bedding (horizontal lines perpendicular to direction of flow)
What type of bedding will sinuous crested ripples produce?
Trough cross-bedding
How do the troughs seen in trough cross-bedding produced by sinuous crested ripples help to determine the correct way up?
A younger trough will down-cut into a pre-existing older trough.
When and where do turbulent eddies form and what can this result in the development of?
Turbulent eddies form when high velocity flow digs out the lee side of a ripple and can result in the development of trough cross-bedding
How can you distinguish between upper flat beds and lower flat beds?
Parting lineation is a feature of upper flow regimes and hence may be seen in upper flat beds but not lower flat beds
Why are antidunes rarely preserved in stratigraphic record?
Antidunes do not sort grain sizes due to an extremely high velocity of flow
What is the difference between lamination and bedding?
Lamination is layering <1cm thick
Bedding is layering >1cm thick
What are 3 types of lamination?
Flaser lamination
Wavy lamination
Lenticular lamination
