kirby geomorph es 09 final4web

8/12/2019 Kirby Geomorph ES 09 FINAL4web

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Geomorphology and Earthscope:

Landscape evolution in the service of geodynamics

Eric KirbyPenn State University

Earthscope Science Planning Workshop


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Tectonic Geomorphology Records of deformation over

103- 106yrs

Bridges geologic andgeodetic timescales Provides information on

spatial wavelength, rates,and historyof topographicchange

Lithospheric deformation at intermediate timescales 2 Approaches:

Displaced debris-flow levee in Panamint Valley

Landforms as markers of deformation

Invert topography for rock uplift

Stolar et al., 2006


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I. Landforms as markers of fault slip

Enabled by newtechnologies LiDAR Geochronology:

(cosmogenic and OSL)- access timescales

between 10 - 200 ka

Bridges geologic andgeodetic timescales

Patterns/rates ofstrain release throughtime

How wide are faults? LiDAR (ALSM) shaded relief of debris-flow - Panamint Valley


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Pace of deformation in western US Geologic studies

reveal variationsin fault slip overtimescales longerthan seismic cycle

Examples from: Southern CA Eastern CA

PBO Geodetic network


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Alternating periods of fault activity

Bennett et al., 2004


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Diffuse dextral shear in eastern CA

T. Dixon


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Transient loading during seismic cluster?

Oskin et al., 2008 - Geology

Dolan et al., 2007 - Geology

Does strain hardening drive alternating periods of activity and quiescence?


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Continued investment is warrantedLiDAR coverage of active faults

R. Malservisi and M. Hackl - data from PBO, USGS, SOPAC, SCEC


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II. Invert topography for rock uplift

Landscape reliefadjusts such thaterosion rate balancesdifferential uplift ofrock

Timescales ~105- 106yr Depend on length

scale of system

What measure oftopography?

Ahnert, 1970

Montgomery and Brandon, 2002


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II Invert topography for rock uplift Relief is scale-dependent

measure that convolveslandscape process-domains

Most relief in activemountain belts on channelnetwork

Channels also governlandscape response tochanges in tectonics,climate

Liwu River, Taiwan

0

3.5 km

30 km


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Tectonic Geomorphology Primer

High erosion rate

Low erosion rate

S=ksA

"#

Duvall, Kirby and Burbank, 2004

Blue ~ 6 mm/yrRed ~ 14 mm/yrOrange ~ 2- 14 mm/yr


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What do we know?


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What do we know?


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Transient Channel Response

Vkp =Uf

1n (Uf "Ui)

Uf1n "Ui

1n

Vkp =Uf

knickpoint

High U

Low U


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Whats in it for you?

Data of Kirby et al., 2003


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Data of Kirby et al., 2003

Joint inversion of InSAR and GPS - Shen et al., 2009


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Kirby et al., in prep


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Kirby et al., in prep

100-200 m/My

600-1200 m/My


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II. Future Directions

Linkages between mantle buoyancy and topography: Vigorous small-scale convection? Removal and/or hydration of mantle lithosphere Edge convection vs. warming of heterogeneous lithosphere

3%

2

1

0

1

2

3

P-wave

fast

slow

B. Schmandt and G. Humphreys


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The challenge

Long wavelength and (relatively) slow rates Subtle signals in landscape Long response timescales

Require interdisciplinary approach combining landscape analysis withproxies for erosion and paleoelevation

W. Ouimet and E. Kirby


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Karlstrom and CREST Working Group, in prep

The opportunity

Rates and spatial scales of topographic change can helpdistinguish processes generating buoyancy (lithosphericheating vs edge convection)


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The opportunity

And hold potential for constraining wavelength ofdeformation


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The opportunity

Uplift history provides bounds on timescale and densitystructure associated with small-scale convection (e.g.,Molnar and Jones, 2004)

Zandt et al., 2004

Stock et al., 2005

Sierra Wallowa Mtns

~2 km uplift

post-CRB

(Hales et al.)

-2 -1 0 1 2% Vp

Schmandt and Humphreys


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II. Future Directions

Persistence of topography in Appalachians: Slow degradation of relict topography?

Paul Bierman et al., Peter Zeitler, Jim Spotila


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Take-home The evolution oflandscape topography

encodes informationabout the pace andwavelength oflithospheric

deformation

History is key Cross-fertilization

among geodynamics,earth structure,geology, climate, andlandscape

kirby geomorph es 09 final4web

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