Effects of Soil Creep on Geomorphologic Evolution

Effects of Soil Creep on Geomorphologic Evolution

Effects of Soil Creep on Geomorphologic Evolution

Leah Edwards 9/25/06

/ Figure 1: Initial Uplift
Diffusivity coefficient = .4
Water erosion = 0
Q1- The driving force of the geomorphologic evolution here is gravity . The initial uplift is a rapid period of uplift that causes steep, straight, rectilinear slopes at the limiting angle (shown here from t=0 to t≈.2). After this, from t≈2 to t=1, there is a slow decrease in the rate of erosion, causing the crest to decrease in height as the steep slopes begin to flatten into rolling hills and piedmont features.
And, tectonic activity can be also a driving force for the initial uplift. 3/3
/ Figure 2: Initial Uplift
Diffusivity coefficient = .1
Water erosion = 0
Figure 1 and Figure 2 were created using the same initial uplift program. The only difference is the value of the diffusivity coefficients.


Distance x / Figure 3: Spatial Profiles- Cross-Sectional View of Figures 1 and 2
Green line- Kg = .1 (Fig 2)
Blue line- Kg = .4 (Fig 1)
Q2- Part 1- When t = .5, the height of the first mountain (in which Kg = .4) has decreased from its crest to about .015. Also at t = .5, the height of the second mountain (in which Kg = .1) has decreased from its crest only to about .04. Therefore, when Kg is greater, there is more soil erosion that causes the mountain to decrease in height faster than when Kg is smaller. 3/3


Time t / Figure 4: Temporal Profiles- Cross-Sectional View of Figures 1 and 2
Q2- Part 2- When x = .5, the height of the first mountain (in which Kg = .4) peaks at t≈.2 at a height of about .055. It then decreases exponentially as time continues until it reaches a height of almost 0. The second mountain (in which Kg = .1), also peaks at t≈.2 but at a greater maximum height than the first mountain, at about .075. Thereafter, it decreases at a slightly lesser steep exponential slope, and ends at about .025. Therefore, we can say that when Kg is greater, the mountain cannot reach peaks as high as when Kg is smaller because the limiting angle is reached sooner and soil creep begins to bring down the height of the mountain at a slightly faster rate.
/ Figure 5: Quick and Brief Uplift
Diffusivity coefficient = .3
Rapid uplift shown here causes the mountain to reach its limiting angle, at which point it reaches peak height (at t≈.2) and then begins to decrease in height due to soil creep (from t≈.2 to t=1).
/ Figure 6: Persistent Uplift
Diffusivity coefficient = .3
Persistent uplift shown here causes the mountain to rise continually. As time progresses from t=0 to t=1, the rate of uplift is slowing down because as the slopes get steeper, there will be more soil creep bringing the height down. This mountain looks very close to reaching its limiting angle because the rate of uplift is becoming almost level. At this point, soil creep will begin to cause the height to decrease.
/ Figure 7: Temporal Profiles- Cross-Sectional View of Persistent Uplift
Q3- When x = .5, the mountain with a diffusivity coefficient of .2 increases in height beginning at time t=.1, with a decreasing rate as time goes on, until it reaches a height of .25 at t=1. The mountain with Kg=.5 increases in height beginning at the same time as the first mountain, but with a much less steep upward slope, becoming almost completely level at a height of .125 by the time t=1. Therefore, we can conclude that when Kg is greater, soil creep keeps the mountain from uplifting as much as when Kg is smaller. Good. But, you missed the temporal profiles of height driven by two different uplift source. 1.5/3

Q4- Geomorphologic structures differ greatly when they are created by either rapid or persistent uplift. Soil creep always as the same effect, bringing down the height of a mountain and making steeper slopes into more rolling piedmont structures. For both rapid and persistent uplift, the diffusivity coefficient determines the maximum height (Nope. Both the strenth of tectonic uplift and the soil diffusivity determine.)that the mountain will reach; a greater Kg gives a lower maximum height. How quickly it reaches that maximum point depends on whether it is rapid or persistent uplift. A greater Kg gives a faster rate of soil erosion, meaning that for rapid uplift, the mountain will flatten more quickly, and for persistent uplift, the mountain will rise less quickly (if the tectonic uplift is weak, the height can decline even with the persistent uplift). 3/3

Total:

10.5/12 = / 8.8