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!