Topic 3: Slope processes and Landforms

Question 1

What is a slope?

Answer 1

• a discrete component of the ground surface defined principally by the angle it makes with a horizontal plane

Question 2

What is the catena concept?

Answer 2

• landscapes are really a combination of different slope forms, and slopes are produced by raindrop impact, water, and matter flow.
• catena is a 2d model of redistribution of water and matter in a landscape

Question 3

A Shoulder has ____ ______ curvature, a backslope has _____ curvature, and a foot slope has _____ ______ curvature

Answer 3

A Shoulder has high convex curvature, a backslope has low curvature, and a foot slope has high concave curvature

Question 4

Curvature is …..

Answer 4

rate of change in a slope

Question 5

What is topography?

Answer 5

• the study of the forms and features of land surfaces
• topography of an area may refer to the landforms and features itself, or a description or depiction in maps
• also could include the change in elevation

Question 6

when shear force exceeds shear strength…..

Answer 6

sediment will move

Question 7

For Slopes:
F = 1 is ___________
F > 1 is ______ ________
F < 1 is an ______ __________

Answer 7

F = 1 is equilibrium
F > 1 is stable slope
F < 1 is an unstable slope

Question 8

What are some things that reduce shear strength?

Answer 8

• reduced cohesion
• increased pore water pressure (reduces matric forces that hold soil together - does not act as lubricant)
• increased weathering (creases more space)

Question 9

What are some things that increase stress?

Answer 9

• added weight, vibrations (depositions, tectonics, humans)
• increase in gradient, increase in slope (erosion, humans)

Question 10

The more cohesive a material……

Answer 10

the harder it is to move

Question 11

fine grained materials (sand and smaller) can be solid, elastic, plastic, or fluid, depending on …..

Answer 11

moisture content

Question 12

What are atterberg limits?

Answer 12

• limits where materials change phase between solid, plastic, liquid, etc.

Question 13

Why does water content influence Atterberg limits for fine grained materials?

Answer 13

• matrix forces keeps fine grained materials “stuck” together
• if water is added, volume of the material increases, as sediments have pores
• matrix forces ‘leave’ , state of material changes

Question 14

What are the two types of sediment transport on slopes?

Answer 14

• diffusive transport
• advective transport

Question 15

What is diffusive transport?

Answer 15

• sediment transport spread over a wide area
• creep, rainsplash (rain hitting sediment, it moves), biogenic processes,

Question 16

What is advective transport?

Answer 16

• sediment transport that is concentrated in one area
• channels, gullies

Question 17

What controls transport on slopes? How?

Answer 17

• weathering (parent materials - how susceptible is the material to weathering)
• climate (related to cohesion (wetness of material), temperature is also a facture.)
• vegetation (bare slopes with no vegetation/roots are more suseptible sediment transportation)
• relief (strength of gravity and sheer stress, the greater the difference the stronger gravity will be)

Question 18

What is diamict structure?

Answer 18

When materials are mixed together and we have a massive structure, that is poorly sorted, with different clast sizes. Both colluvium (slope) and Till (glacial) are related to diamict

Question 19

what are some types of landforms associated with slope movements?

Answer 19

• topples
• slides
• spreads
• flows
• gelifluction (slope deformation)

Question 20

What is a rotational slump?

Answer 20

• type of slide, where material does not fall all the way down
• have a shear surface where the surface is curved
• stress and strain relationship changes along the curved area
• the slide moves downward and outward, moves a bunch of material along the way
• tends to rejuvenate landscapes.

Question 21

What are rock falls?

Answer 21

• rapidly dropping, leaping, bouncing, rolling descents of material
• mainly thru the air from steep cliffs
• planes of weakness exploited in insitu material

Question 22

What are topples?

Answer 22

• similar to rock falls, but forward movement of a material block is produced by slow rotation around a fixed hinge
• common when joints, beds, cleavage, sip into the slope

Question 23

What is a slide?

Answer 23

• movement of large slabs/blocks or unconsolidated regolith, often parallel to natural surfaces
• material slips over one or more sufaces

Question 24

What are retrogressive thaw slumps?

Answer 24

• a slump that is driven by melting permafrost in the ground
• space between sediment grains are filled with ice, which melts, and then the cohesion falls apart
• as it melts more and more, more slump is created, and more is exposed

Question 25

what are translational slides

Answer 25

• shear surface gently sloping flat plane, usually plane of weakness
• one material on top, second different type underneath, top material slides off

Question 26

what are flows?

Answer 26

• applied stress deforms a physical substance in an irreversible manner
• movement is similar to a viscous fluid, velocity decreases with depth
• usually involve water, but can happen with dry materials
• low frequency, high impact event

Question 27

what is a debris flow?

Answer 27

• a moving mass of loose mud, sand, soil, rock, water, and air that travels down a slope under the influence of gravity
• very rapid, moving material must ‘flow’
• not very well sorted material, mixed grain size

Question 28

What is quick clay/ leda clay?

Answer 28

• type of flow event
• Marine clays with high water content
• made of clays without strong bonds - quartz, feldspars, micas
• stable under they are shocked, disturbed, or salts are leached out
• entire flats of land will just collapse

Question 29

What is the role of landslides in landscape evolution and ecology?

Answer 29

• redistribute sediment
• alter hydrology
• change weathering profiles
• change topography