Uncovering signatures of geomorphic process through high resolution topography





Stuart W. D. Grieve, University of Edinburgh

Not a solo effort

pit pit pit

And many others...

Landslide recurrance intervals

pit

Need to understand the geometry of hillslopes

Low hanging fruit!

How can we measure hillslope length?

A ruler?

Slope-area plots?

Drainage density?

Flow routing?

study_areas
study_areas
study_areas
study_areas

A ruler?

Hovius

Time consuming

Subjective

Doesn't consider topography

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

SA

Slope-area plots?

Picking an inflection point?

Binning or smoothing the data

Converting an area to a length

Lots of variability in results

Drainage density?

$$D_D = \frac{L_T}{A} $$

$$L_H \approx (2D_D)^{-1} $$

Drainage density?

DD

Drainage density?

Little spatial variation

Sensitive to channel network

Doesn't account for channel width

Underestimates hillslope length

Flow routing?

3d
  • Measure hillslope length as a flow path

  • Connect ridges to channels

Flow routing?

traces

Flow routing?

HFR

Flow routing?

Can be applied at a fine spatial scale

Accounts for local topography

Not subjective

The best method is flow routing, so what?

comparison

Flow routing gives us other data

schematic

This data means we can test sediment flux laws

Sediment flux

google_earth
  • Volume of sediment transported on a hillslope per unit area in a period of time

  • Sediment flux controls:

    • Geometry of hillslopes

    • Landscape response to climate and tectonic forcing

    • Landscape evolution modelling

Sediment flux laws

Constraining linear flux

mckean small

Constraining nonlinear flux

roering_1999 roering_2001

Topographic predictions of linear sediment flux

Topographic predictions of nonlinear sediment flux

Predictions of the relief structure of landscapes

fig_10
fig_10
fig_10
fig_10

Topography is consistent with nonlinear sediment flux

LH_R example
  • Demonstrated at a landscape scale

  • Can be applied anywhere

  • First test that relies only on topographic data

  • Supports Roering's model

paper1

How else can this data be used?

roering_2007

Can we do this with more than 2 data points?

$$ E^* = \frac{-2 \color{red}{C_{HT}L_H}}{S_C}\ \ \ \ \ \ \ \ \ \ \ \ R^* = \frac{\color{red}{R}}{S_{C}\color{red}{L_H}} $$


Test of nonlinear sediment flux

Identify tectonic characteristics of landscapes

Understand variablilty of landscape properties

gm_er
gm_er
gm_er
or_er
or_er

More evidence for nonlinear sediment flux!

Detecting uplift and decay

E_R_schematic

Why do the Appalachians exist?

200 million years since uplift ceased

landscape waterfall

Why do the Appalachians exist?

Theory 1: Uplift is still happening, just slowly

Theory 2: Topographic rejuvenation in the Miocene

nc_er
nc_er
nc_er

Evidence of topographic decay?

Tentatively supports the theory of Miocene rejuvenation

paper2

Conclusions

Topography has lots of information about process

Using only topographic data we can:

Falsify flux laws

Identify tectonics

fig_10 nc_er

We need reproducible methods to exploit this information

LSD
lsdtopotools.github.io

The project you start isn't always the project you finish!

pit pit