Title: GSA Short Course: Tectonic Geomorphology
1GSA Short CourseTectonic Geomorphology
Acknowledgements Cam Wobus Ben Crosby Eric
Kirby Daniel Sheehan Kelin Whipple Noah
Snyder Will Ouimet Nicole Gasparini Roman
DiBiase Funding NSF GLD
2Topographic Metrics
- Many Topographic metrics have been proposed.
Well examine the three most common - Channel Steepness Index
- Hillslope Gradients
- Local Relief at Various Scales
- What are the relationships among these?
- Which are most useful for gaging the influence of
tectonics on topography?
3Course Outline
- Presentation I why rivers determining channel
steepness - Analysis of Model Topographies
- Discussion
- Presentation II relations among erosion rate,
channel steepness, hillslope gradients, and local
relief - Analysis of Real Topography
- Discussion
- Presentation III distinguishing spatial from
temporal effects
480-90 Relief is on Bedrock Channels
Blue lines drainage area gt 1km2
580-90 Relief is on Bedrock Channels
Threshold hillslope gradients dominate no
tectonic info
6Now in 3D
- The Same Drainage Basin in Taiwan
7Historical Context
- River profiles generally smooth, concave-up
- Debate z(x) power law, logarithmic, semi-log
- Hack semi-log
- Hack Gradient Index SL (slopelength)
- Differentiate once evaluate at x L
-
-
Deviations from constant gt lithologic, tectonic
effects
8Historical Context
- Hacks Law (1957)
-
- Flints Law (1974)
-
- Generalization of Hacks semi-log profile
thus ks replaces SL index - Combine above relations
-
- IFF
Integrate Once
9SL index Can Vary Downstream simply due to Basin
Shape
10Fluvial Scaling Empirical Data
- Empirical data for well-adjusted fluvial systems
around the globe yield the following scaling - S ksA-q
- Linear relationship between log(S) and log(A)
- ks is the channel steepness q is the concavity
11Flints Law Mixed Bedrock-Alluvial Stream
(Appalachians, VA)
12Flints Law Mixed Bedrock-Alluvial Stream
(Appalachians, VA)
S ksA-q
colluvial reach
ks
-q
ks is a more-general equivalent to the SL
index No dependence on basin shape
13Duvall, Kirby, and Burbank, 2004, JGR-ES
q
S ksA-q
ks
14King Range Concavity Invariant with Rock Uplift
Rate
Snyder et al, 2000, GSABDirectly Contradicts
Earlier Finding of Merritts and Vincent, 1989,
GSAB
15Steepness varies with U
Concavity invariant with U
Debris-flow chutes expand with U
161. Extract raw channel profile data
Source USGS 10 m DEM (Free!)
Solution Original Contour Crossings
17Raw Pixel-to-Pixel Slopes, USGS 10m
182. Resample at a constant contour interval and
regress on linear segment
Grey raw data Black 30m contour crossings
19Similar scaling from a variety of data sources
Blue USGS 10 m DEM
Red SRTM 90 m DEM (720 m downstream moving
average)
20Problem Co-variation of ks and q
- Can not compare ks among streams with even
slightly different concavities - Solution Need a Normalized Steepness Index
determined with a reference concavity (use
regional mean) -
21ksn
Sklar and Dietrich, 1998
22Estimating ksn Uncertainty
- The Integral Method
- integrate once
-
-
- Regress z on c, slope of line is ksn
- Uncertainty on ksn fit by regression is best
measure of goodness of fit (2s reported)
23Variation in Concavity Index
- Blind regression from headwaters to outlet,
concavity varies widely - 0.2 1.2, and locally up to very high 6
- Recognizing interpretable spatial and transient
effects - 0.4 0.6 captures most data
- Effects debris-flow chutes lithology (x)
uplift (x) transient response to uplift (t) or
climate (t)
24Flints Law Mixed Bedrock-Alluvial Stream
(Appalachians, VA)
S ksA-q
colluvial reach
ks
-q
ks is a more-general equivalent to the SL
index No dependence on basin shape
25- Transient systems
- Knickpoint in long profile
- Break in slope-area scaling
E KAmSn
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28Channel Steepness Index Spatial Information
about Relative Rock Uplift Rate
- Siwalik Hills, Nepal
- San Gabriel Mountains, CA
Nepal Himalaya (Wobus et al.) Olympic Mountains,
WA (Gasparini and Brandon) Bolivian Andes (Safran
et al) Santa Ynez Mtns, CA (Duvall et al) King
Range, CA (Snyder et al) Eastern Margin, Tibetan
Plateau (Ouimet et al)
29Siwalik Hills, Nepal
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31Bagmati Transect
Bakeya Transect
Data from Lave and Avouac, 2000, JGR
32Siwalik Hills Anticline Himalaya Foreland, Nepal
Strike-Parallel Uniform Uplift Along Stream
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35Strike-Parallel Normal, uniform concavity
14 mm/yr
7 mm/yr
Strike-Parallel Steepness varies with U
36Siwalik Hills, Nepal
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38Transverse U(x) Reflected in Concavity
39Eastern margin of the Tibetan Plateau A
Transient Landscape deep river gorges cut into
an uplifted, slowly eroding, low-relief relict
landscape. fluvial dissection has not
propagated through the entire landscape. rivers
typically transition from the relict landscape
into dissected gorges bounded by steep hillslopes.
Patches of low-relief, relict landscape preserved
in eastern Tibet (Clark, 2003).
Mean, high elevation relict topography
40Slope map from SRTM 90 m DEM
Transient Hillslopes
Hillslopes, following incision, display zones
of adjustment with steepest values in the
lowermost reaches of individual basins
4
41- Zhong Qing River Transient hillslope and river
profile response -
- Tributary of the Dadu River
- 70 km long, 1500 m of fluvial relief
- Total Area 930 km2
A
B
Google Earth
Longitudinal River Profile from 90 m SRTM
42Transient Morphology Photos from the Zhong Qing
and Li Qui Rivers
2 Initial Dissection
1 Relict Landscape
3 Transition (Gentle)
6 Gorge Landscape
5 Transition (Steep)
4 Transition (Intermediate)
43125 km
Ouimet, Whipple, Granger Tues 8am 63 Basin Wide
Erosion Rates Mean Drainage Area 38 km2
Erosion Rate (m/Ma)
4435 Erosion Rates (out of 70 total) 4 samples are
greater than 1km/Ma (1mm/yr) Plotted here are
all samples (31) less than 600 m/Ma, 0.6 mm/yr
4563 Basins ------------------- 2 rates 3000 m/Ma
Gonga Shan ------------------- Rate error Bars 1s
Snyder et al, 2003 Theoretical Curve
Roering et al, 2001 Theoretical Curve
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47Example Tectonic Geomorphology of the San
Gabriel Mountains
48Shaded Relief with Color Elevation
Active FaultsThickness Most Recent Known Slip
49San Gabriel Mountains Shaded Relief
Preliminary Detrital Cosmogenic 10Be Sample
Catchments Transparent Overlay
50Hillslope Gradient (30x30m)
51Beware Many authors use hillslope relief and
local relief (measured over up to 5km radius)
as interchangeable
52Local Relief (r 100m)
53Hillslope Gradient (30x30m)
54Slope calculated as Relief/diameter (R/200)
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57Local Relief (r 1km)
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59Local Relief (r 2.5km)
60Background Color Elevation, Streams by
Normalized Steepness Index
Note abrupt steepness breaks across active
faults, no break where inactive/slow