Lecture 16 - Hillslope Processes Continued

Question 1

Define Slope

Answer 1

-An exposed ground surface that stands at an angle with the horizontal

Question 2

What is the Difference between Infinite and Finite Slopes?

Answer 2

-Infinite = extends over a great distance meaning the length is much larger than the depth of the surface of rupture
-Finite = The depth of the surface of rupture is comparable to the length of the slope

Question 3

What is the Safety Factor?

Answer 3

-Represented as F which means the ratio between the shear strength (sum of resisting forces) and shear stress (sum of forces moving material downslope)
-F value of 1.3 or more means the slope is stable; anything less it is unstable

Question 4

What is Shear Strength?

Answer 4

-The vertical component of gravity and cohesion between soil particles
-Vegetation increases cohesion and therefore shear strength

Question 5

What is Shear Stress?

Answer 5

-Component of gravity downslope and the lack of friction between soil particles

Question 6

How does Water affect these two variables?

Answer 6

-Decreases friction between soil and rock
-Increases shear stress due to weight
-Decreases soil cohesion

Question 7

Define a Long Runout Landslide

Answer 7

-Mass of rock and soil travelling unexpectedly lengthy horizontal distances after a comparatively short vertical fall

Question 8

Define a Slump

Answer 8

-When a portion of the slope moves downhill as a cohesive block along a curved surface of rupture

Question 9

Define a Debris Flow

Answer 9

-Mass of rock and soil and water travelling down a slope often triggered by heavy rains
-Common in arid areas, where rock is exposed for long periods of time, unprotected by vegetation and sudden rain could mobilise it