Down-stream process transition (f (q ) = 1) · 2020-01-29 · 2) Acr 10-2 103 4 5 Detachment...
Transcript of Down-stream process transition (f (q ) = 1) · 2020-01-29 · 2) Acr 10-2 103 4 5 Detachment...
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2)
Acr
10-2
103 104 105
Detachment Limited Equilibrium Slope
Sd = ksd A-�d
St = kst A-�t Slope
Detachment Limited Sd >> St
Sd << St Stochastic
Down-stream process transition (f (qs) = 1)
106 107 108
10-1
Cha
nnel
Gra
dien
t (m
/m) {
Drainage Area (m
Transport Limited Equilibrium
Transport Limited
Variation
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Mixed Bedrock-Alluvial Stream (Appalachians, VA)
Concavity Index indistinguishable from detachment-limited bedrock channels
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Available data suggests DL and TL streams have similar concavities
θ = .69
θ = .49
θ = .42
Courtesy of The Geological Society of America. Used with permission.
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King Range Trunk Streams
No Change in Form, Double Steepness
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Tributary Response: Kinematic Wave
U2/U1 ~ 8; Why ks2/ks1 ~ 2?
Sediment Armor in Low Uplift Zone?
Threshold Stress for Erosion?
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Tectonic Geomorphology
• Intermediate Timescale Patterns and Rates of Deformation
• Bridge between Geodetic and Geologic • 1e3 – 1e6 years • Spatial and Temporal Resolution
• Paleoseismicity / Tsunami Records • Interaction of Climate and Tectonics
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Intermediate Timescale Deformation
Approaches
• Static Landforms as Strain Gauges• Terraces (fill/strath, fans, marine platforms, coral reefs,
moraines, etc)
• Dynamic Topography – Invert for Rock Uplift• Bedrock and Alluvial Channel Networks • Colluvial Channels • Hillslopes • Glacial Cirques and Valleys
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Intermediate Timescale Deformation
Problems
• Local/Regional Patterns and Rates of Rock Uplift• Fault Behavior and Slip Rates
– Kinematics and temporal evolution
• Interaction of Structures – Linkage, rupture across segment boundaries
• Off-Fault Deformation and Distributed Strain • Slip Rates and Paleoseismicity of Blind Thrusts • Role of Lower Crustal and/or Mantle Flow
– Little / no record in upper crustal structures
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Interaction of Climate and Tectonics Problems
• Does Erosion Dictate Rock Uplift Rate / Pattern?
• Nature and Strength of Feedbacks – Uplift – Topography – Climate – Erosion - Uplift
• Do Details of the Erosion Mechanism Matter? – Bedrock Channels; Sediment flux; Debris Flows; Glaciers
• Steady State Orogens – Plausible? Probable? Time to Steady State?
• Impact of Late Cenozoic Climate Change • Controls on Topographic Relief
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Research NeedsErosion Processes and Climate Linkages
• Bedrock Channel Erosion Laws (role lithology, sediment flux, sediment size, debris flows, storms)
• Glacial Erosion Mechanics (glacier flux, ice dynamics, hydrology)
• Landslide Initiation and Inventory (storms, seismic acceleration)
• Extreme Events and Orography (storms, glacier outburst floods, landslide dam-bream floods)
• Controls on River and Terrace Gradient (climate vs. tectonics; channel width)
• Chemical and Physical Weathering Relationship
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Research NeedsChronology
• Cosmogenic Isotope Methodologies » Inheritance, Production Rates, Multiple Systems
• In-Situ / Detrital Thermochronology
• U-Th/He Dating of Young Volcanics
• Relief Evolution » Topography, Denudation Rate, Isotherm Structure and their
Temporal Evolution » Near Surface Thermal Advection
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Tectonic GeomorphologyData Needs
• Development of Chronometers and Centers for Analyses, Digital Compilation/Distribution of Data
• Affordable High-Resolution Satellite Data (ASTER, INSAR)
• High-Resolution DEMs (LIDAR, SRTM, ASTER)• Digital Geologic Maps • Dense Arrays Climate Data (Orography) • Digital Mapping Technologies (e.g., PDA, Laser Range
Finder, GPS Total Station) • GPR – Shallow Structures
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Himalaya Foreland, Nepal Siwalik Hills Anticline
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Modeled Erosion Rates
Courtesy of The Geological Society of America. Used with permission.
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Modeled Erosion Rates
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Sediment Flux Lag Complicates Landscape Response –Transient Shifts from Sediment Covered to Tool Starved Likely
SC
Mix
TS
SC – Sediment Covered TS – Tool starved
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Sediment-flux Models: Required Low-Uplift Zone Conditions for ks2/ks1 = 2
Tool Starved
Sediment Covered
Peak Efficiency
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Generalized Stream-Power Incision Model
Tool Starved
Sediment Covered
Qs > Qc Transport Limited
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2)
Log Gradient
Stream power
Linear decline, n=1
Linear decline, n=2
Beaumont
Parabolic, n=1
Parabolic, n=2
-2.5 -2 -1.5 -1 -0.5 0 5
6
7
8
9
�t = 0
Diagnostic steady-state morphology IF �t < �d
Log
Dra
inag
e Are
a (m
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Log Gradient
Stream power
Linear decline, n=1
Linear decline, n=2
Parabolic, n=1
Parabolic, n=2
5 -2.5 -2 -1.5 -1 -0.5 0
6
7
8
9
�t = 0.3
2)
Steady-state morphology non-diagnostic IF �t ~ �d
Log
Dra
inag
e Are
a (m
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Topographic Sensitivity to Uplift Rate Potentially Diagnostic
SC
TS
Mix
SC – Sediment Covered TS – Tool starved