Effect of erosion on mountain building Background on work budget Background on erosion Erosion exercise Data analysis
Dec 29, 2015
Effect of erosion on mountain building
Background on work budget
Background on erosion
Erosion exercise
Data analysis
Is the Earth Lazy?
whatever
Do fault systems evolve in order to minimize the total work?
Evidence of lazy Earth
Geometry of spreading centers [Sleep, 1979] and mudcracks reflects work minimization
Faults become more smooth with greater slip
Strike-slip traces [e.g. Wesnousky, 1988], extensional fault traces [Gupta et al., 1998], and lab [Scholz, 1990].
Forces within wedges
Work terms
Underthrust-Accretion Cycle
a) Accretion: new forethrust
b) Underthrusting
c) Accretion: new forethrust
d) Underthrusting
Sandbox experiments
Adams et al. 2001, JSG
Particle Integrated Velocity records the development of accreting forethrust within10 cm of contraction
Model Set-Up
Simulate 0.5 cm of contraction
Forethrust
Thrust Sheet Growth
Conclusions thus far…
Sandboxes are lazy!The Earth might be
lazy.
?
Equilibrium
At equilibrium the ratio of wedge thickness to wedge length is constant.
Erosion can disrupt this equilibrium
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6 8 10 12 14
displacement (cm)
wedge thickness/length
high frictionlow friction
Erosion
Iceland
Erosion
Watch Mario movie
Erosion Experiment
# turns Displacement (cm)
Wedge thickness
Wedge length
Wedge thickness
Wedge length
0 0
20
40
60
erosion
80
100
120
Implications
After erosion the wedge thickens rather than lengthening. Can accommodate contraction efficiently along the old faults
On the non-erosion side, wedge must constantly lengthen because the old faults are buried under heavy sand.
Fault system adjusts to slip along the most efficient path <- earth is lazy!