Systematic Landform Response to Uplift Along the Dragon

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Systematic Landform Response to Uplift Along the
Dragons Back Pressure Ridge, Carrizo Plain,
California, Imaged Using High-Resolution LiDAR
Topographic Data

• HILLEY, G. E., Department of Geological and
  Environmental Sciences, Stanford University
• ARROWSMITH, J R., Department of Geological
  Sciences, Arizona State University

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Motivation

• What can topography tell us about the rates and
  distributions of active rock uplift? What might
  be important complicating factors that may leave
  important imprints in the landscape (e.g.,
  changes in geomorphic processes, mechanical and
  hydrologic heterogeneity of underlying
  bedrock/substrate, climatic variations)?
• How does a landscape respond to changes in rock
  uplift rate? How long might these changes take
  to be assimilated into the topography of these
  areas?

Approach

• Quantify changes in topographic form associated
  with changes in rock uplift rates in places that
  the latter can be constrained reliably.
• Relate these topographic changes to changes in
  rock uplift rate and associated changes in
  geomorphic process.

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The San Andreas Fault in Central / Southern
California
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SAF Field Trip
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Active Seismicity Along the SAF
Arrowsmith, unpublished data
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Fault Geometry and Distribution of Landforms
Arrowsmith, unpublished data
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The Northern Elkhorn Hills LiDAR Dataset
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Structure and Active Deformation in the NEH
Arrowsmith, unpublished data
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The Dragons Back Pressure Ridge
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Geology of Dragons Back
Arrowsmith, 1995
Qoa - Quaternary Older Alluvium QTP - Paso Robles
Formation (undiff.) QTPg - Gold member of Paso
Robles Formation QTPt - Tan member of Paso Robles
Formation QTPp - Pink member of Paso Robles
Formation
Stratigraphically highest to lowest members
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Subsurface Geometry of Structures
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Kinematics of Dragons Back
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Topographic Response to Rock Uplift
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Channel Response to Rock Uplift
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Erosional Process Response
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Erosional and Topographic Response to Rock Uplift
Hilley and Arrowsmith, 2008
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Changes in Concavity in Response to Changes in
Rock Uplift Rate
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Summary of Erosional Process Changes in Topography

• Hillslope processes are dominated by landsliding
  after 6 kyr after onset of rock uplift.
• Channels become well-established by 16-23 kyr and
  are oversteepened by 40 kyr.
• Channel gradients diminish after 11-14 kyr after
  uplift ceases. This incision oversteepenes local
  hillslope and triggers landsliding.
• Landsliding becomes subdued after 60-71 kyr after
  peak rock uplift rates have been experienced.

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Threshold Landscape Model
Dietrich et al., 1992
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Threshold Processes Along the DB
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Topographic and Erosional Response to Changes in
Rock Uplift
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Summary

• Landscapes in unconsolidated, homogeneous
  materials undergo predictable, systematic changes
  in topographic parameters and erosional processes
  in response to changes in rock uplift rates.
• By implication, topographic metrics in such
  environments may by used to infer rock uplift
  rates related to tectonic activity.
• Importantly, changes in erosional processes may
  introduce lags between changes in rock uplift
  rates and changes in topographic metrics. For
  example, the rapid response of channels relative
  to hillslopes may undermine hillslopes after rock
  uplift has ceased, trigger pervasive landsliding,
  and increase basin relief metrics that otherwise
  might be indicative of high rock uplift rates.
• High-resolution LiDAR topography may be used to
  study the relationships between rock uplift rates
  and topographic form, and the resulting changes
  in geomorphic processes.