UMaine SECS Numerical Modeling Laboratory - User contributions [en]

File:MitchellPrelim.png

2016-12-07T13:29:47Z

Sam:

Gulf of Maine Hydrology

2016-12-07T13:29:19Z

Sam:

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2016-05-09T04:19:14Z

Sam:

Gulf of Maine Hydrology

2016-05-09T04:18:03Z

Sam:

File:MedomakGIUH2.png

2016-05-09T03:16:41Z

Sam:

Gulf of Maine Hydrology

2016-05-09T03:16:22Z

Sam:

Gulf of Maine Hydrology

2016-05-09T02:26:19Z

Sam:

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2016-05-09T01:40:54Z

Sam:

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2016-05-09T01:39:52Z

Sam:

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2016-05-09T01:39:10Z

Sam:

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2016-05-09T01:38:06Z

Sam:

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2016-05-09T01:36:36Z

Sam:

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2016-05-09T01:35:33Z

Sam:

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2016-05-09T01:34:32Z

Sam:

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2016-05-09T01:32:42Z

Sam:

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2016-05-09T01:29:08Z

Sam:

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2016-05-09T01:25:59Z

Sam:

Gulf of Maine Hydrology

2016-05-09T01:25:36Z

Sam: Created page with "File:aspectratio.png File:da_est_rat.png File:drainagedensity05.png File:drainscore.png File:fdeveloped.png File:qest.png [[File:reliefratio.png]..."

University of Maine SECS Numerical Laboratory

2016-02-18T02:32:20Z

Sam:

'''Welcome to UMaine Geodynamics!'''

This wiki is a means for accessing research and educational modules produced by the geodynamics group at UMaine.
Follow links on the navigation pane to the left to search through our various research projects.

[[New Results|News:]]

2/17/15: Sam Roy made revisions to [[Tectonic-Geomorphic-Climatic Interaction (NSF-EAR-1324637, 1323137)]]

10/28/15: An "Events" section has been added to the sidebar in anticipation of the upcoming GeoPRISMS collaborative session at UMaine. Participants can find session announcements and links to PDFs on the [[GeoPRISMS Workshop 2015]] page.

10/1/15: Lynn Kaluzienski created "[[Smoothed Particle Hydrodynamics|Smoothed Particle Hydrodynamics]]," complete with model descriptions and animations.
{| class="wikitable"
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9/17/15: Sam Roy updated text and model results in [[Subduction Zone Dynamics in the Mantle and at the Earth's Surface]]:
{| class="wikitable"
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5/26/15: fault motion and landscape evolution model results have been updated: [[The role of surface displacement in landscape evolution]]

3/26/15: Sam Roy added modeling work on Mantle Wedge Hydration under "Previous Research": [[Mantle Wedge Hydration]]

3/18/15: Sam Roy and Nick Richmond have been running coupled FLAC/CHILD models to investigate orographic precipitation. Stay tuned!

[[File:itsonlyamodel.png]]

(http://www.funnyjunk.com/)

Consult the [//meta.wikimedia.org/wiki/Help:Contents User's Guide] for information on using the wiki software.

== Getting started ==
* [//www.mediawiki.org/wiki/Manual:Configuration_settings Configuration settings list]
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Mantle Wedge Hydration

2016-02-18T02:13:27Z

Sam:

<div style="font-size:150%">
'''Mantle wedge hydration and its effects on mineralogy and rheology'''

Sam Roy, 11/21/2011, University of Maine School of Earth and Climate Sciences

'''1. Introduction'''

Though considered to be a secondary influence behind temperature and strain rate (Billen, 2008), water does play an important role in mantle wedge rheology. Water released from a subducting oceanic lithosphere quickly saturates the mantle wedge, allows the creation of stable hydrous phases, and reduces viscosity by as much as 2 orders of magnitude (Arcay et al., 2006). The excess water that is not dissolved in the wedge continues to migrate upward into the overlying plate, where it can cause thermal erosion. I explore the effects of water on the mantle wedge through a thermal-mechanical model of Yakutat block subduction under the North American plate and use pseudosections to determine the amount of water to be released by the subducting slab. The influence on viscosity is then explored using a flow law that considers water abundance within the pre-exponential coefficient.

'''2. Thermal-Mechanical Model''' [[File:slab_Page_1.jpg|200px|thumb|Figure 1]]

A thermal-mechanical model is used as a 2D spatial framework for temperature and pressure that can be used to determine the expected phase assemblages within pseudosections. The model used is from Abers et al. (2006) and is meant to replicate the subduction front of the Yakutat block located beneath southern Alaska (Figure 1a). Plate geometry was attained by seismic tomography. The mantle wedge viscosity is based on a non-Newtonian dry olivine dislocation creep flow law. The mantle is coupled to the subducting and overriding slabs except within the wedge nose, where a mechanically brittle mantle is host to localized frictional sliding between plate and wedge. The geothermal gradient and advective heat transfer from wedge flow control thermal gradients within the subduction zone, and 17 mW m-2 of heat generation comes from shear heating along the fault (Figure 1b). Plate velocity is 55 mm a-1 (Nuvel-1A). The oceanic crust is 16 km thick.

'''3. H2O saturated MORB Phase Assemblage Analysis''' [[File:slab_Page_2.jpg|250px|thumb|left|Table 1]] [[File:slab_Page_3.jpg|400px|thumb|Figure 2]]

I use an average bulk rock composition for north Pacific MORB from Melson et al. (1976) as a surrogate for Yakutat plate composition (Table 1). MORB compositions typically do not vary except for REE abundances which would not affect this study. The subducting MORB can experience large pressure and temperature ranges. The oceanic plate is host to excessive hydrothermal advection at the rift zone in addition to water percolation into normal faults that form by crustal bending at the trench and is therefore considered to be saturated in H2O when it subducts (Schmidt and Poli, 1998; Arcay et al., 2005).
Bulk rock composition data is used to determine phase stability in Perple_X, a thermodynamic calculation program, to determine which phases have the lowest Gibbs free energy within a specified temperature and pressure range (Connolly, 2009). I used the hp04ver.dat database file (Holland and Powell, 1998) and the solut09.dat solution model file to create pressure versus temperature pseudosections for both MORB and mantle compositions. Considered solution models for the MORB composition are listed in Table 2 and the resulting pseudosections are shown in Figure 2a-c.
Water is held in the rock’s crystal structure until lawsonite is reacted out at higher T and P, but the release of water is gradual, as seen by the red contours (Figure 2a). Lawsonite (Figure 2b) holds about 11.5 wt% water at ultrahigh pressures and can make up to 33 wt% of the entire rock at relatively high pressure and low temperature, therefore it is an important factor in mantle wedge hydration and its abundance controls H2O abundance at high pressure (Pawley and Holloway, 1993). Lawsonite abundance decreases with increasing temperature until it is completely reacted out to form eclogite facies rock. Dehydration and compression also increases the plate’s negative buoyancy (Figure 2c).
Figure 2d displays the same pseudosection but with PT paths for three positions (top, middle, and base) in the MORB crust. The starting position of the arrows is dependent on pressure at depth and temperature in the steady-state oceanic crust geothermal gradient. Plate subduction leads to a reversal of the geothermal gradient by rapid thermal advection from wedge flow into the top of the subducting slab. The plate passes through greenschist, amphibolite, blueschist, and finally eclogite facies when all water is dehydrated, and the stable phase assemblages are typical for the basaltic rendition of these facies (Schmidt and Poli, 1998). The top of the MORB crust quickly dehydrates at ~30 kbar and releases 4.55 wt% H2O, as does the center of the plate at ~50 kbar (Figure 2e). The base of the MORB crust dehydrates at ~68 kbar, but releases only 2 wt% H2O due to its initially hotter temperature. Water is released from the subducting slab continuously until the depth of 200 km (~68 kbar).

[[File:slab_Page_4.jpg|300px|thumb|left|Figure 3]] '''4. H2O Saturated Subducting Mantle Phase Assemblage Analysis'''

Figure 3 displays the pseudosection for a saturated mantle composition (Hoffman, 1988). I also consider the subducting mantle to be saturated due to hydrothermal advection at the rift zone. There is a thin (~1km) layer of mantle lying right below the MORB crust that contains ~60 wt% Serpentinite, holding ~8.5 wt% H2O. Although thin, this layer holds a very large proportion of the subducting slab water budget, and the chemical discontinuituy between MORB and serpentinized mantle can lead to decoupling in some situations (Billen, 2008). Amphibole is stable within deeper parts of the mantle but it holds only miniscule amounts of water. Both the 1km thick serpentinized mantle layer and the 16km thick MORB crust contain a total average of 4.96 wt% H2O that can be released into the upper mantle.

'''5. H2O Limited Mantle Wedge Phase Assemblage Analysis''' [[File:slab_Page_5.jpg|400px|thumb|Figure 4]]

The water content (Table 1) used to create the mantle wedge pseudosection (Figure 4a) is limited to the amount of water that is released by lawsonite and serpentinite dehydration in the subducting slab (4.96 wt%). The blue line of Figure 4a represents the transition from all water utilized in hydrous phase assemblages to a water saturated system that requires less water. Serpentinite is restricted to a maximum of 29.46 wt% (rather than the maximum 60 wt% for a saturated mantle) within the blue range due to the limited amount of water within the wedge. The cold wedge nose also contains chlorite and amphibole (Figure 4b), and is the only location within the wedge where water is held in the crystal structure (Figure 4c). All water that is released under the wedge is taken into hydrous phases, therefore no excess water remains in the wedge nose. The red line represents the last dehydration reactions before a completely anhydrous mineral assemblage becomes stable. The only water that can exist within the rock beyond this point is dissolved water locked within olivine, cpx, opx, or garnet, and is limited to 0.146 wt% (Arcay et al., 2005; 2006).

[[File:slab_Page_6.jpg|250px|thumb|left|Figure 5]] '''6. H2O Effects on Viscosity'''

Mantle viscosity is reduced by the introduction of water according to the viscosity equation of Figure 5. The equation takes into account the weakening factor of hydration through the pre-exponential coefficient. The weakening factor controls the drop in viscosity through a given weight percent of water. Although temperature and strain rate are the major components that control viscosity, water can alter viscosity values by 1 order of magnitude if dissolved water is present, or 2 orders of magnitude if water is able to enter the crystal structure of a hydrous mineral (e.g., Arcay et al., 2005; 2006). All hydrous minerals exist at low temperatures, therefore their reduction in viscosity is negligible because their viscosity value is already several orders of magnitude larger. Water enhances transportability of ions and reduces cohesion between grains, allowing for more efficient diffusion and dislocation creep mechanisms under constant strain (Arcay et al., 2006; Manea and Gurnis, 2007). This contrasts with the non-Newtonian dry olivine dislocation creep flow law used in the Arcay et al. (2005) model, therefore the thermal gradients produced therein would be altered in a wet wedge system.
Additionally, hydration leads to a reduced solidus for mantle compositions and can lead to melt which further reduces wedge viscosity. Melt can occur within the wedge where temperatures are highest, but reduced wedge viscosity will enhance thermal advection into the now hydrous overlying plate and initiate low viscosity mechanics and melting there as well (Billen, 2008).

'''7. Concluding Remarks'''

Water should be expected in abundance within all subduction zones, and it has large effects on mantle wedge mineralogy and rheology. Water is released predominantly by dehydration of lawsonite in the MORB crust and serpentinite in the upper layer of the subducting mantle. Hydration allows growth of serpentinite and other hydrous minerals in the wedge nose, which leads to flow decoupling between the wedge and the subducting plate. Dehydration of the subducting slab leads to seismisity at greater depths (Abers et al., 2005). H2O dissolution in the anhydrous mantle wedge mineral assemblage can reduce viscosity by 1-2 orders of magnitude on top of the enhanced ability to advect heat more rapidly. Finally, excess water not taken into the wedge, which is substantial, is driven upward into the overlying plate, leading to thermal erosion and melting at its base, which will lead to volcanism and extension of the backarc.
</div>

'''8. Bibliography'''

Abers, G.; van Keken, P; Kneller, E.; Ferris, A.; Stachnik, J. (2006). The thermal structure of subduction zones constrained by seismic imaging: implications for slab dehydration and wedge flow. Earth and Planetary Science letters 241: 387-397.

Arcay, D; Doin, M.; Tric, E.; Bousquet, R.; de Capitani, C. (2006). Overriding plate thinning in subduction zones: localized convection induced by slab dehydration. Geochemistry, Geophysics, Geosystems 7.2.

Arcay, D.; Tric, E.; Doin, M. (2005). Numerical simulations of subduction zones effect of slab dehydration on the mantle wedge dynamics. Physics of the Earth and Planetary Interiors 149: 133-153.

Billen, M.I. (2008). Modeling the dynamics of subducting slabs. Annual Reviews of Earth and Planetary Sciences 36: 325-356.

Connolly, J. A. D. (2009) The geodynamic equation of state: what and how. Geochemistry, Geophysics, Geosystems 10:Q10014 DOI:10.1029/2009GC002540.

Hoffman, P. (1988). Archean oceanic flake tectonics. Geophysical Research Letters 15.10: 1077-1080.

Holland, T. J. B., & Powell, R. (1998) An internally consistent thermodynamic data set for phases of petrological interest. Journal of Metamorphic Geology 16:309-343.

Manea, V. and Gurnis, M. (2007). Subduction zone evolution and low viscosity wedges and channels. Earth and Planetary Science Letters 264: 22-45.

Melson, W.; Vallier, T.; Wright, T.; Byerly, G.; Nelen, J. (1976). Chemical diversity of abyssal volcanic glass erupted along the Pacific, Atlantic, and Indian ocean seafloor spreading centers. In the Geophysics of the Pacific Ocean Basin, Geophysical Monograph series, Washington (AGU) 14: 351-368.

Pawley, A. and Holloway, J. (1993). Water sources for subduction zone volcanism: new experimental constraints. Science 260.5108: 664-667.

Schmidt, M. and Poli, S. (1998). Experimentally based water budgets for dehydrating slabs and consequences for arc magma generation. Earth and Planetary Science Letters 163: 361-379.

The role of rock mass strength in landscape evolution

2016-02-18T02:10:14Z

Sam:

'''The influence of crustal strength fields on the patterns and rates of fluvial incision'''

'''From:'''

[http://umaine.edu/earthclimate/files/2013/09/roy-et-al-2015.pdf Roy, S.G., Koons, P.O., Upton, P., Tucker, G.E. (2015). The influence of crustal strength fields on patterns and rates of fluvial incision. Journal of Geophysical Research: Earth Surface 120, 275-299, doi 10.1002/2014JF003281.]

S.G. Roy (a), P.O. Koons (a), P. Upton (b,a), G.E. Tucker (c)

a ''Earth and Climate Sciences, University of Maine, 111 Bryand Global Sci. Ctr., Orono ME 04469''

b ''GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand''

c ''Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado, UCB 399 Boulder, CO 80309-0399''

'''Video: erosion of fault with 30 degree dip angle'''
{{#ev:youtube|6UsBabkbLI8}}

'''Abstract'''

Gradients in the bedrock strength field are increasingly recognized as integral to the rates and patterns of landscape evolution. To explore this influence, we incorporate data from fault strength profiles into a landscape evolution model, under the assumption that erodibility of rock is proportional to the inverse square root of cohesion for bedrock rivers incised by bedload abrasion. Our model calculations illustrate how patterns in the crustal strength field can play a dominant role in local fluvial erosion rates and consequently the development of fluvial network patterns. Fluvial incision within weak zones can be orders of magnitude faster than for resistant bedrock. The large difference in erosion rate leads to the formation of a straight, high order channel with short, orthogonal tributaries of low order. In comparison, channels incising into homogeneous strength fields produce dendritic drainage patterns with no directional dependence associated with erodibility gradients. Channels that cross the strength gradient experience local variations in knickpoint migration rate and the development of stationary knickpoints. Structurally confined channels can shift laterally if they incise into weak zones with a shallow dip angle, and this effect is strongly dependent on the magnitude of the strength difference, the dip angle, and the symmetry and thickness of the weak zone. The influence of the strength field on drainage network patterns becomes less apparent for erodibility gradients that approach homogeneity. There are multiple natural examples with drainage network patterns similar to those seen in our numerical experiments.
{| class="wikitable"
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| [[File:Figure1.png|300px|thumb|left|Figure 1]]
| [[File:Figure2.jpg|300px|thumb|left|Figure 2]]
| [[File:Figure3.jpg|300px|thumb|left|Figure 3]]
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| [[File:Figure4.jpg|300px|thumb|left|Figure 4]]
| [[File:Figure5.jpg|300px|thumb|left|Figure 5]]
| [[File:Figure6.jpg|300px|thumb|left|Figure 6]]
|}
Video 1: homogeneous strength landscape
{{#ev:youtube|7LxnHcFQRA8}}

Video 2: faulted landscape
{{#ev:youtube|EQyNMReW4Ms}}

The role of rock mass strength in landscape evolution

2016-02-18T02:09:50Z

Sam:

'''The influence of crustal strength fields on the patterns and rates of fluvial incision'''

'''From:'''

[http://umaine.edu/earthclimate/files/2013/09/roy-et-al-2015.pdf Roy, S.G., Koons, P.O., Upton, P., Tucker, G.E. (2015). The influence of crustal strength fields on patterns and rates of fluvial incision. Journal of Geophysical Research: Earth Surface 120, 275-299, doi 10.1002/2014JF003281.]

S.G. Roy (a), P.O. Koons (a), P. Upton (b,a), G.E. Tucker (c)

a ''Earth and Climate Sciences, University of Maine, 111 Bryand Global Sci. Ctr., Orono ME 04469''

b ''GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand''

c ''Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado, UCB 399 Boulder, CO 80309-0399''

Video 3: erosion of fault with 30 degree dip angle
{{#ev:youtube|6UsBabkbLI8}}

'''Abstract'''

Gradients in the bedrock strength field are increasingly recognized as integral to the rates and patterns of landscape evolution. To explore this influence, we incorporate data from fault strength profiles into a landscape evolution model, under the assumption that erodibility of rock is proportional to the inverse square root of cohesion for bedrock rivers incised by bedload abrasion. Our model calculations illustrate how patterns in the crustal strength field can play a dominant role in local fluvial erosion rates and consequently the development of fluvial network patterns. Fluvial incision within weak zones can be orders of magnitude faster than for resistant bedrock. The large difference in erosion rate leads to the formation of a straight, high order channel with short, orthogonal tributaries of low order. In comparison, channels incising into homogeneous strength fields produce dendritic drainage patterns with no directional dependence associated with erodibility gradients. Channels that cross the strength gradient experience local variations in knickpoint migration rate and the development of stationary knickpoints. Structurally confined channels can shift laterally if they incise into weak zones with a shallow dip angle, and this effect is strongly dependent on the magnitude of the strength difference, the dip angle, and the symmetry and thickness of the weak zone. The influence of the strength field on drainage network patterns becomes less apparent for erodibility gradients that approach homogeneity. There are multiple natural examples with drainage network patterns similar to those seen in our numerical experiments.
{| class="wikitable"
|-
| [[File:Figure1.png|300px|thumb|left|Figure 1]]
| [[File:Figure2.jpg|300px|thumb|left|Figure 2]]
| [[File:Figure3.jpg|300px|thumb|left|Figure 3]]
|-
| [[File:Figure4.jpg|300px|thumb|left|Figure 4]]
| [[File:Figure5.jpg|300px|thumb|left|Figure 5]]
| [[File:Figure6.jpg|300px|thumb|left|Figure 6]]
|}
Video 1: homogeneous strength landscape
{{#ev:youtube|7LxnHcFQRA8}}

Video 2: faulted landscape
{{#ev:youtube|EQyNMReW4Ms}}

The combined influence of rock damage and surface displacement in landscape evolution

2016-02-18T01:48:50Z

Sam:

'''Dynamic links between rock damage, erosion, and strain during orogenesis'''

Roy, S.G.1; Koons, P.O.1; Upton, P.1,2; Tucker, G.E.3

1. Earth and Climate Sciences, University of Maine

2. GNS Science

3. Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado

[[File:dynamic-02.png|500px|thumb|right|Geodynamic models incorporating homogeneous and heterogeneous erodibility. Heterogeneous erodibility is a function of the total plastic strain field. Orogenesis creates asymmetric precipitation patterns. Localized erosion in shear zones leads to reduced vertical coordinate normal stress, greater strain localization.]]
The mechanical properties of the lithosphere are increasingly recognized as having a quantifiable influence on the rates and patterns of surface processes. Strain localization, controlled by the mechanical response to local tectonic and topographic stress fields, manifests as tabular fault damage zones that impose displacement, strength, and grain size distribution patterns on the Earth’s surface. Brittle failure and comminution associated with seismogenic cataclasis can reduce bedrock cohesion by several orders of magnitude and generate dense fracture networks, such that the grains released by rock weathering are much finer than those produced by weathering of the surrounding undamaged, intact bedrock. We combine models of landscape evolution and crustal mechanics to investigate how strain-induced crustal failure can exert significant controls on the rates and patterns of landscape development and adjustment. Based on our model results, drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion and transport of fault gouge. Fault erosion can be over an order of magnitude faster than erosion of intact bedrock. Fault zones with shallow dip angle are capable of enforcing lateral migration of their structurally confined rivers. Deep valleys created by eroding faults quickly become armored by coarse sediments transported from nearby intact bedrock. Differential displacement affects drainage network patterns by deforming and uplifting the surface relative to baselevel while simultaneously exposing fresh fault damage zones. Topography produced from these processes reflects the strong mechanical anisotropy associated with strain localization and brittle failure over many length scales, contrasting with the absence of a strong directional dependence from dendritic rivers incising into a predominantly homogeneous substrate.

{{#ev:youtube|i6otd3N3S00}} {{#ev:youtube|goV9XIw2Ie0}}

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The combined influence of rock damage and surface displacement in landscape evolution

2016-02-18T01:42:38Z

Sam:

'''Dynamic links between rock damage, erosion, and strain during orogenesis'''

Roy, S.G.1; Koons, P.O.1; Upton, P.1,2; Tucker, G.E.3

1. Earth and Climate Sciences, University of Maine

2. GNS Science

3. Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado

[[File:dynamic-02.png|500px|thumb|right|Geodynamic models incorporating homogeneous and heterogeneous erodibility. Heterogeneous erodibility is a function of the total plastic strain field. Orogenesis creates asymmetric precipitation patterns. Localized erosion in shear zones leads to reduced vertical coordinate normal stress, greater strain localization.]]
The mechanical properties of the lithosphere are increasingly recognized as having a quantifiable influence on the rates and patterns of surface processes. Strain localization, controlled by the mechanical response to local tectonic and topographic stress fields, manifests as tabular fault damage zones that impose displacement, strength, and grain size distribution patterns on the Earth’s surface. Brittle failure and comminution associated with seismogenic cataclasis can reduce bedrock cohesion by several orders of magnitude and generate dense fracture networks, such that the grains released by rock weathering are much finer than those produced by weathering of the surrounding undamaged, intact bedrock. We combine models of landscape evolution and crustal mechanics to investigate how strain-induced crustal failure can exert significant controls on the rates and patterns of landscape development and adjustment. Based on our model results, drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion and transport of fault gouge. Fault erosion can be over an order of magnitude faster than erosion of intact bedrock. Fault zones with shallow dip angle are capable of enforcing lateral migration of their structurally confined rivers. Deep valleys created by eroding faults quickly become armored by coarse sediments transported from nearby intact bedrock. Differential displacement affects drainage network patterns by deforming and uplifting the surface relative to baselevel while simultaneously exposing fresh fault damage zones. Topography produced from these processes reflects the strong mechanical anisotropy associated with strain localization and brittle failure over many length scales, contrasting with the absence of a strong directional dependence from dendritic rivers incising into a predominantly homogeneous substrate.

<gallery heights=1000 widths=500>
File:panel1a.jpg
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Video 1
{{#ev:youtube|7LxnHcFQRA8}}

Video 2
{{#ev:youtube|atHQFLGXAnI}}

Video 3
{{#ev:youtube|EQyNMReW4Ms}}

Video 4
{{#ev:youtube|OGSEdAoEMgQ}}

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{{#ev:youtube|ScBrWlDLHqc}}

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{{#ev:youtube|1MedsrUVmIs}}

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{{#ev:youtube|v05nZENkgFQ}}

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{{#ev:youtube|Tx9ndPzBiPw}}

Video 12
{{#ev:youtube|_RJ9h0kgcZI}}

The combined influence of rock damage and surface displacement in landscape evolution

2016-02-18T01:42:25Z

Sam:

'''Dynamic links between rock damage, erosion, and strain during orogenesis'''

Roy, S.G.1; Koons, P.O.1; Upton, P.1,2; Tucker, G.E.3

1. Earth and Climate Sciences, University of Maine

2. GNS Science

3. Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado

[[File:dynamic-02.png|500px|thumb|right|Geodynamic models incorporating homogeneous and heterogeneous erodibility. Heterogeneous erodibility is a function of the total plastic strain field. Orogenesis creates asymmetric precipitation patterns. Localized erosion in shear zones leads to reduced vertical coordinate normal stress, greater strain localization.]]
The mechanical properties of the lithosphere are increasingly recognized as having a quantifiable influence on the rates and patterns of surface processes. Strain localization, controlled by the mechanical response to local tectonic and topographic stress fields, manifests as tabular fault damage zones that impose displacement, strength, and grain size distribution patterns on the Earth’s surface. Brittle failure and comminution associated with seismogenic cataclasis can reduce bedrock cohesion by several orders of magnitude and generate dense fracture networks, such that the grains released by rock weathering are much finer than those produced by weathering of the surrounding undamaged, intact bedrock. We combine models of landscape evolution and crustal mechanics to investigate how strain-induced crustal failure can exert significant controls on the rates and patterns of landscape development and adjustment. Based on our model results, drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion and transport of fault gouge. Fault erosion can be over an order of magnitude faster than erosion of intact bedrock. Fault zones with shallow dip angle are capable of enforcing lateral migration of their structurally confined rivers. Deep valleys created by eroding faults quickly become armored by coarse sediments transported from nearby intact bedrock. Differential displacement affects drainage network patterns by deforming and uplifting the surface relative to baselevel while simultaneously exposing fresh fault damage zones. Topography produced from these processes reflects the strong mechanical anisotropy associated with strain localization and brittle failure over many length scales, contrasting with the absence of a strong directional dependence from dendritic rivers incising into a predominantly homogeneous substrate.

<gallery heights=1000 widths=500>
File:panel1a.jpg
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</gallery>

Video 1
{{#ev:youtube|7LxnHcFQRA8}}

Video 2
{{#ev:youtube|atHQFLGXAnI}}

Video 3
{{#ev:youtube|EQyNMReW4Ms}}

Video 4
{{#ev:youtube|OGSEdAoEMgQ}}

Video 5
{{#ev:youtube|ScBrWlDLHqc}}

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{{#ev:youtube|DrCawThGbc0}}

Video 7
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{{#ev:youtube|mIMDFTv6D1Y}}

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{{#ev:youtube|1MedsrUVmIs}}

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{{#ev:youtube|_RJ9h0kgcZI}}

The combined influence of rock damage and surface displacement in landscape evolution

2016-02-18T01:41:49Z

Sam:

'''Dynamic links between rock damage, erosion, and strain during orogenesis'''

Roy, S.G.1; Koons, P.O.1; Upton, P.1,2; Tucker, G.E.3

1. Earth and Climate Sciences, University of Maine

2. GNS Science

3. Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado

[[File:dynamic-02.png|500px|thumb|left|Geodynamic models incorporating homogeneous and heterogeneous erodibility. Heterogeneous erodibility is a function of the total plastic strain field. Orogenesis creates asymmetric precipitation patterns. Localized erosion in shear zones leads to reduced vertical coordinate normal stress, greater strain localization.]]
The mechanical properties of the lithosphere are increasingly recognized as having a quantifiable influence on the rates and patterns of surface processes. Strain localization, controlled by the mechanical response to local tectonic and topographic stress fields, manifests as tabular fault damage zones that impose displacement, strength, and grain size distribution patterns on the Earth’s surface. Brittle failure and comminution associated with seismogenic cataclasis can reduce bedrock cohesion by several orders of magnitude and generate dense fracture networks, such that the grains released by rock weathering are much finer than those produced by weathering of the surrounding undamaged, intact bedrock. We combine models of landscape evolution and crustal mechanics to investigate how strain-induced crustal failure can exert significant controls on the rates and patterns of landscape development and adjustment. Based on our model results, drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion and transport of fault gouge. Fault erosion can be over an order of magnitude faster than erosion of intact bedrock. Fault zones with shallow dip angle are capable of enforcing lateral migration of their structurally confined rivers. Deep valleys created by eroding faults quickly become armored by coarse sediments transported from nearby intact bedrock. Differential displacement affects drainage network patterns by deforming and uplifting the surface relative to baselevel while simultaneously exposing fresh fault damage zones. Topography produced from these processes reflects the strong mechanical anisotropy associated with strain localization and brittle failure over many length scales, contrasting with the absence of a strong directional dependence from dendritic rivers incising into a predominantly homogeneous substrate.

<gallery heights=1000 widths=500>
File:panel1a.jpg
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</gallery>

Video 1
{{#ev:youtube|7LxnHcFQRA8}}

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{{#ev:youtube|atHQFLGXAnI}}

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{{#ev:youtube|EQyNMReW4Ms}}

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{{#ev:youtube|OGSEdAoEMgQ}}

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{{#ev:youtube|ScBrWlDLHqc}}

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{{#ev:youtube|DrCawThGbc0}}

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{{#ev:youtube|6UsBabkbLI8}}

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{{#ev:youtube|mIMDFTv6D1Y}}

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{{#ev:youtube|1MedsrUVmIs}}

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{{#ev:youtube|v05nZENkgFQ}}

Video 11
{{#ev:youtube|Tx9ndPzBiPw}}

Video 12
{{#ev:youtube|_RJ9h0kgcZI}}

The combined influence of rock damage and surface displacement in landscape evolution

2016-02-18T01:40:19Z

Sam:

'''Dynamic links between rock damage, erosion, and strain during orogenesis'''

Roy, S.G.1; Koons, P.O.1; Upton, P.1,2; Tucker, G.E.3

1. Earth and Climate Sciences, University of Maine

2. GNS Science

3. Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado

[[File:dynamic-02.png|500px|thumb|left|Geodynamic models incorporating homogeneous and heterogeneous erodibility. Heterogeneous erodibility is a function of the total plastic strain field. Orogenesis creates asymmetric precipitation patterns. Localized erosion in shear zones leads to greater strain localization.]]
The mechanical properties of the lithosphere are increasingly recognized as having a quantifiable influence on the rates and patterns of surface processes. Strain localization, controlled by the mechanical response to local tectonic and topographic stress fields, manifests as tabular fault damage zones that impose displacement, strength, and grain size distribution patterns on the Earth’s surface. Brittle failure and comminution associated with seismogenic cataclasis can reduce bedrock cohesion by several orders of magnitude and generate dense fracture networks, such that the grains released by rock weathering are much finer than those produced by weathering of the surrounding undamaged, intact bedrock. We combine models of landscape evolution and crustal mechanics to investigate how strain-induced crustal failure can exert significant controls on the rates and patterns of landscape development and adjustment. Based on our model results, drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion and transport of fault gouge. Fault erosion can be over an order of magnitude faster than erosion of intact bedrock. Fault zones with shallow dip angle are capable of enforcing lateral migration of their structurally confined rivers. Deep valleys created by eroding faults quickly become armored by coarse sediments transported from nearby intact bedrock. Differential displacement affects drainage network patterns by deforming and uplifting the surface relative to baselevel while simultaneously exposing fresh fault damage zones. Topography produced from these processes reflects the strong mechanical anisotropy associated with strain localization and brittle failure over many length scales, contrasting with the absence of a strong directional dependence from dendritic rivers incising into a predominantly homogeneous substrate.

<gallery heights=1000 widths=500>
File:panel1a.jpg
File:panel2a.jpg
File:panel3a.jpg
</gallery>

Video 1
{{#ev:youtube|7LxnHcFQRA8}}

Video 2
{{#ev:youtube|atHQFLGXAnI}}

Video 3
{{#ev:youtube|EQyNMReW4Ms}}

Video 4
{{#ev:youtube|OGSEdAoEMgQ}}

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{{#ev:youtube|ScBrWlDLHqc}}

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{{#ev:youtube|DrCawThGbc0}}

Video 7
{{#ev:youtube|6UsBabkbLI8}}

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{{#ev:youtube|mIMDFTv6D1Y}}

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{{#ev:youtube|1MedsrUVmIs}}

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{{#ev:youtube|v05nZENkgFQ}}

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{{#ev:youtube|Tx9ndPzBiPw}}

Video 12
{{#ev:youtube|_RJ9h0kgcZI}}

File:Dynamic-02.png

2016-02-18T01:39:41Z

Sam:

The combined influence of rock damage and surface displacement in landscape evolution

2016-02-18T01:38:42Z

Sam:

'''Dynamic links between rock damage, erosion, and strain during orogenesis'''

Roy, S.G.1; Koons, P.O.1; Upton, P.1,2; Tucker, G.E.3

1. Earth and Climate Sciences, University of Maine

2. GNS Science

3. Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado

[[File:dynamic-02.png|500px|thumb|left|Geodynamic models incorporating homogeneous and heterogeneous erodibility. Heterogeneous erodibility is a function of the total plastic strain field. Orogenesis creates asymmetric precipitation patterns. Localized erosion in shear zones leads to greater strain localization.]]

The mechanical properties of the lithosphere are increasingly recognized as having a quantifiable influence on the rates and patterns of surface processes. Strain localization, controlled by the mechanical response to local tectonic and topographic stress fields, manifests as tabular fault damage zones that impose displacement, strength, and grain size distribution patterns on the Earth’s surface. Brittle failure and comminution associated with seismogenic cataclasis can reduce bedrock cohesion by several orders of magnitude and generate dense fracture networks, such that the grains released by rock weathering are much finer than those produced by weathering of the surrounding undamaged, intact bedrock. We combine models of landscape evolution and crustal mechanics to investigate how strain-induced crustal failure can exert significant controls on the rates and patterns of landscape development and adjustment. Based on our model results, drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion and transport of fault gouge. Fault erosion can be over an order of magnitude faster than erosion of intact bedrock. Fault zones with shallow dip angle are capable of enforcing lateral migration of their structurally confined rivers. Deep valleys created by eroding faults quickly become armored by coarse sediments transported from nearby intact bedrock. Differential displacement affects drainage network patterns by deforming and uplifting the surface relative to baselevel while simultaneously exposing fresh fault damage zones. Topography produced from these processes reflects the strong mechanical anisotropy associated with strain localization and brittle failure over many length scales, contrasting with the absence of a strong directional dependence from dendritic rivers incising into a predominantly homogeneous substrate.

<gallery heights=1000 widths=500>
File:panel1a.jpg
File:panel2a.jpg
File:panel3a.jpg
</gallery>

Video 1
{{#ev:youtube|7LxnHcFQRA8}}

Video 2
{{#ev:youtube|atHQFLGXAnI}}

Video 3
{{#ev:youtube|EQyNMReW4Ms}}

Video 4
{{#ev:youtube|OGSEdAoEMgQ}}

Video 5
{{#ev:youtube|ScBrWlDLHqc}}

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{{#ev:youtube|DrCawThGbc0}}

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{{#ev:youtube|6UsBabkbLI8}}

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{{#ev:youtube|mIMDFTv6D1Y}}

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{{#ev:youtube|1MedsrUVmIs}}

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{{#ev:youtube|Tx9ndPzBiPw}}

Video 12
{{#ev:youtube|_RJ9h0kgcZI}}

The combined influence of rock damage and surface displacement in landscape evolution

2016-02-18T01:35:05Z

Sam:

'''Dynamic links between rock damage, erosion, and strain during orogenesis'''

Roy, S.G.1; Koons, P.O.1; Upton, P.1,2; Tucker, G.E.3

1. Earth and Climate Sciences, University of Maine

2. GNS Science

3. Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado

The mechanical properties of the lithosphere are increasingly recognized as having a quantifiable influence on the rates and patterns of surface processes. Strain localization, controlled by the mechanical response to local tectonic and topographic stress fields, manifests as tabular fault damage zones that impose displacement, strength, and grain size distribution patterns on the Earth’s surface. Brittle failure and comminution associated with seismogenic cataclasis can reduce bedrock cohesion by several orders of magnitude and generate dense fracture networks, such that the grains released by rock weathering are much finer than those produced by weathering of the surrounding undamaged, intact bedrock. We combine models of landscape evolution and crustal mechanics to investigate how strain-induced crustal failure can exert significant controls on the rates and patterns of landscape development and adjustment. Based on our model results, drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion and transport of fault gouge. Fault erosion can be over an order of magnitude faster than erosion of intact bedrock. Fault zones with shallow dip angle are capable of enforcing lateral migration of their structurally confined rivers. Deep valleys created by eroding faults quickly become armored by coarse sediments transported from nearby intact bedrock. Differential displacement affects drainage network patterns by deforming and uplifting the surface relative to baselevel while simultaneously exposing fresh fault damage zones. Topography produced from these processes reflects the strong mechanical anisotropy associated with strain localization and brittle failure over many length scales, contrasting with the absence of a strong directional dependence from dendritic rivers incising into a predominantly homogeneous substrate.

<gallery heights=1000 widths=500>
File:panel1a.jpg
File:panel2a.jpg
File:panel3a.jpg
</gallery>

Video 1
{{#ev:youtube|7LxnHcFQRA8}}

Video 2
{{#ev:youtube|atHQFLGXAnI}}

Video 3
{{#ev:youtube|EQyNMReW4Ms}}

Video 4
{{#ev:youtube|OGSEdAoEMgQ}}

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{{#ev:youtube|ScBrWlDLHqc}}

Video 6
{{#ev:youtube|DrCawThGbc0}}

Video 7
{{#ev:youtube|6UsBabkbLI8}}

Video 8
{{#ev:youtube|mIMDFTv6D1Y}}

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{{#ev:youtube|1MedsrUVmIs}}

Video 10
{{#ev:youtube|v05nZENkgFQ}}

Video 11
{{#ev:youtube|Tx9ndPzBiPw}}

Video 12
{{#ev:youtube|_RJ9h0kgcZI}}

Topographic Anisotropy

2016-02-18T01:30:22Z

Sam:

[http://www.nsf.gov/awardsearch/showAward?AWD_ID=1027809 NSF-CDI-1027809]

'''Multi-scale characterization of topographic anisotropy'''

S.G. Roy (a), P.O. Koons (a), B. Osti (a), P. Upton (b), G.E. Tucker (c)

a ''Earth and Climate Sciences, University of Maine''

b ''GNS Science''

c ''Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado''

{{#ev:youtube|gkpHdrtumgw}} {{#ev:youtube|e86ZIqox_Fk}}

'''Abstract'''

We present a method for quantifying orientation and scale dependence of topographic anisotropy to aid in differentiation of the fluvial and tectonic contributions to surface evolution. Using multi-directional variogram statistics to track the spatial persistence of elevation values across a landscape, we calculate anisotropy as a multiscale, direction-sensitive variance in elevation between two points on a surface. Tectonically derived topographic anisotropy is associated with the three-dimensional kinematic field, which contributes 1) differential surface displacement and 2) crustal weakening along shear zones, both of which amplify processes of surface erosion. Based on our analysis, tectonic displacements dominate the topographic field at the scale of mountain ranges, while a combination of the local displacement and strength fields are well represented at the ridge and valley scale. Drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion of faults and differential displacement across the fault. The persistence and complexity of correlated anisotropic signals depends on how the strain field evolves with time: new tectonic regimes can overprint the original topographic signal, or the signal can slowly recede as tectonism halts. Regions that have been largely devoid of strain, such as passive coastal margins, have predominantly isotropic topography with typically dendritic drainage network patterns. These methods can be used successfully to infer the settings of past or present tectonic regimes, and can be particularly useful in predicting the location and orientation of structural features that would otherwise be impossible to interpret in the field.

<gallery mode=packed-hover widths=1500px>
Image:Vario figures copy Page 01.png|''[[Topographic Anisotropy Figure 1|'''Figure 1''']]''|link=[[Topographic Anisotropy Figure 1]]
Image:Vario figures copy Page 02.png|''[[Topographic Anisotropy Figure 2|'''Figure 2''']]''|link=[[Topographic Anisotropy Figure 2]]
Image:Vario figures copy Page 03.png|''[[Topographic Anisotropy Figure 3|'''Figure 3''']]''|link=[[Topographic Anisotropy Figure 3]]
Image:Vario figures copy Page 04.png|''[[Topographic Anisotropy Figure 4|'''Figure 4''']]''|link=[[Topographic Anisotropy Figure 4]]
Image:Vario figures copy Page 05.png|''[[Topographic Anisotropy Figure 5|'''Figure 5''']]''|link=[[Topographic Anisotropy Figure 5]]
Image:Vario figures copy Page 06.png|''[[Topographic Anisotropy Figure 6|'''Figure 6''']]''|link=[[Topographic Anisotropy Figure 6]]
Image:Vario figures copy Page 07.png|''[[Topographic Anisotropy Figure 7|'''Figure 7''']]''|link=[[Topographic Anisotropy Figure 7]]
Image:Vario figures copy Page 08.png|''[[Topographic Anisotropy Figure 8|'''Figure 8''']]''|link=[[Topographic Anisotropy Figure 8]]
Image:Vario figures copy Page 09.png|''[[Topographic Anisotropy Figure 9|'''Figure 9''']]''|link=[[Topographic Anisotropy Figure 9]]
Image:Vario figures copy Page 10.png|''[[Topographic Anisotropy Figure 10|'''Figure 10''']]''|link=[[Topographic Anisotropy Figure 10]]
</gallery>

Topographic Anisotropy

2016-02-18T01:29:08Z

Sam:

[http://www.nsf.gov/awardsearch/showAward?AWD_ID=1027809 NSF-CDI-1027809]

{{#ev:youtube|gkpHdrtumgw}} {{#ev:youtube|e86ZIqox_Fk}}

'''Multi-scale characterization of topographic anisotropy'''

S.G. Roy (a), P.O. Koons (a), B. Osti (a), P. Upton (b), G.E. Tucker (c)

a ''Earth and Climate Sciences, University of Maine, 111 Bryand Global Sci. Ctr., Orono ME 04469''

b ''GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand''

c ''Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado, UCB 399 Boulder, CO 80309-0399''

'''Abstract'''

We present a method for quantifying orientation and scale dependence of topographic anisotropy to aid in differentiation of the fluvial and tectonic contributions to surface evolution. Using multi-directional variogram statistics to track the spatial persistence of elevation values across a landscape, we calculate anisotropy as a multiscale, direction-sensitive variance in elevation between two points on a surface. Tectonically derived topographic anisotropy is associated with the three-dimensional kinematic field, which contributes 1) differential surface displacement and 2) crustal weakening along shear zones, both of which amplify processes of surface erosion. Based on our analysis, tectonic displacements dominate the topographic field at the scale of mountain ranges, while a combination of the local displacement and strength fields are well represented at the ridge and valley scale. Drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion of faults and differential displacement across the fault. The persistence and complexity of correlated anisotropic signals depends on how the strain field evolves with time: new tectonic regimes can overprint the original topographic signal, or the signal can slowly recede as tectonism halts. Regions that have been largely devoid of strain, such as passive coastal margins, have predominantly isotropic topography with typically dendritic drainage network patterns. These methods can be used successfully to infer the settings of past or present tectonic regimes, and can be particularly useful in predicting the location and orientation of structural features that would otherwise be impossible to interpret in the field.

<gallery mode=packed-hover widths=1500px>
Image:Vario figures copy Page 01.png|''[[Topographic Anisotropy Figure 1|'''Figure 1''']]''|link=[[Topographic Anisotropy Figure 1]]
Image:Vario figures copy Page 02.png|''[[Topographic Anisotropy Figure 2|'''Figure 2''']]''|link=[[Topographic Anisotropy Figure 2]]
Image:Vario figures copy Page 03.png|''[[Topographic Anisotropy Figure 3|'''Figure 3''']]''|link=[[Topographic Anisotropy Figure 3]]
Image:Vario figures copy Page 04.png|''[[Topographic Anisotropy Figure 4|'''Figure 4''']]''|link=[[Topographic Anisotropy Figure 4]]
Image:Vario figures copy Page 05.png|''[[Topographic Anisotropy Figure 5|'''Figure 5''']]''|link=[[Topographic Anisotropy Figure 5]]
Image:Vario figures copy Page 06.png|''[[Topographic Anisotropy Figure 6|'''Figure 6''']]''|link=[[Topographic Anisotropy Figure 6]]
Image:Vario figures copy Page 07.png|''[[Topographic Anisotropy Figure 7|'''Figure 7''']]''|link=[[Topographic Anisotropy Figure 7]]
Image:Vario figures copy Page 08.png|''[[Topographic Anisotropy Figure 8|'''Figure 8''']]''|link=[[Topographic Anisotropy Figure 8]]
Image:Vario figures copy Page 09.png|''[[Topographic Anisotropy Figure 9|'''Figure 9''']]''|link=[[Topographic Anisotropy Figure 9]]
Image:Vario figures copy Page 10.png|''[[Topographic Anisotropy Figure 10|'''Figure 10''']]''|link=[[Topographic Anisotropy Figure 10]]
</gallery>

Topographic Anisotropy

2016-02-18T01:26:44Z

Sam:

[http://www.nsf.gov/awardsearch/showAward?AWD_ID=1027809 NSF-CDI-1027809]

[https://youtu.be/gkpHdrtumgw] [https://youtu.be/e86ZIqox_Fk]

'''Multi-scale characterization of topographic anisotropy'''

S.G. Roy (a), P.O. Koons (a), B. Osti (a), P. Upton (b), G.E. Tucker (c)

a ''Earth and Climate Sciences, University of Maine, 111 Bryand Global Sci. Ctr., Orono ME 04469''

b ''GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand''

c ''Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado, UCB 399 Boulder, CO 80309-0399''

'''Abstract'''

We present a method for quantifying orientation and scale dependence of topographic anisotropy to aid in differentiation of the fluvial and tectonic contributions to surface evolution. Using multi-directional variogram statistics to track the spatial persistence of elevation values across a landscape, we calculate anisotropy as a multiscale, direction-sensitive variance in elevation between two points on a surface. Tectonically derived topographic anisotropy is associated with the three-dimensional kinematic field, which contributes 1) differential surface displacement and 2) crustal weakening along shear zones, both of which amplify processes of surface erosion. Based on our analysis, tectonic displacements dominate the topographic field at the scale of mountain ranges, while a combination of the local displacement and strength fields are well represented at the ridge and valley scale. Drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion of faults and differential displacement across the fault. The persistence and complexity of correlated anisotropic signals depends on how the strain field evolves with time: new tectonic regimes can overprint the original topographic signal, or the signal can slowly recede as tectonism halts. Regions that have been largely devoid of strain, such as passive coastal margins, have predominantly isotropic topography with typically dendritic drainage network patterns. These methods can be used successfully to infer the settings of past or present tectonic regimes, and can be particularly useful in predicting the location and orientation of structural features that would otherwise be impossible to interpret in the field.

<gallery mode=packed-hover widths=1500px>
Image:Vario figures copy Page 01.png|''[[Topographic Anisotropy Figure 1|'''Figure 1''']]''|link=[[Topographic Anisotropy Figure 1]]
Image:Vario figures copy Page 02.png|''[[Topographic Anisotropy Figure 2|'''Figure 2''']]''|link=[[Topographic Anisotropy Figure 2]]
Image:Vario figures copy Page 03.png|''[[Topographic Anisotropy Figure 3|'''Figure 3''']]''|link=[[Topographic Anisotropy Figure 3]]
Image:Vario figures copy Page 04.png|''[[Topographic Anisotropy Figure 4|'''Figure 4''']]''|link=[[Topographic Anisotropy Figure 4]]
Image:Vario figures copy Page 05.png|''[[Topographic Anisotropy Figure 5|'''Figure 5''']]''|link=[[Topographic Anisotropy Figure 5]]
Image:Vario figures copy Page 06.png|''[[Topographic Anisotropy Figure 6|'''Figure 6''']]''|link=[[Topographic Anisotropy Figure 6]]
Image:Vario figures copy Page 07.png|''[[Topographic Anisotropy Figure 7|'''Figure 7''']]''|link=[[Topographic Anisotropy Figure 7]]
Image:Vario figures copy Page 08.png|''[[Topographic Anisotropy Figure 8|'''Figure 8''']]''|link=[[Topographic Anisotropy Figure 8]]
Image:Vario figures copy Page 09.png|''[[Topographic Anisotropy Figure 9|'''Figure 9''']]''|link=[[Topographic Anisotropy Figure 9]]
Image:Vario figures copy Page 10.png|''[[Topographic Anisotropy Figure 10|'''Figure 10''']]''|link=[[Topographic Anisotropy Figure 10]]
</gallery>

Topographic Anisotropy

2016-02-18T01:26:12Z

Sam:

[http://www.nsf.gov/awardsearch/showAward?AWD_ID=1027809 NSF-CDI-1027809]

[https://youtu.be/gkpHdrtumgw]

'''Multi-scale characterization of topographic anisotropy'''

S.G. Roy (a), P.O. Koons (a), B. Osti (a), P. Upton (b), G.E. Tucker (c)

a ''Earth and Climate Sciences, University of Maine, 111 Bryand Global Sci. Ctr., Orono ME 04469''

b ''GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand''

c ''Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado, UCB 399 Boulder, CO 80309-0399''

'''Abstract'''

We present a method for quantifying orientation and scale dependence of topographic anisotropy to aid in differentiation of the fluvial and tectonic contributions to surface evolution. Using multi-directional variogram statistics to track the spatial persistence of elevation values across a landscape, we calculate anisotropy as a multiscale, direction-sensitive variance in elevation between two points on a surface. Tectonically derived topographic anisotropy is associated with the three-dimensional kinematic field, which contributes 1) differential surface displacement and 2) crustal weakening along shear zones, both of which amplify processes of surface erosion. Based on our analysis, tectonic displacements dominate the topographic field at the scale of mountain ranges, while a combination of the local displacement and strength fields are well represented at the ridge and valley scale. Drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion of faults and differential displacement across the fault. The persistence and complexity of correlated anisotropic signals depends on how the strain field evolves with time: new tectonic regimes can overprint the original topographic signal, or the signal can slowly recede as tectonism halts. Regions that have been largely devoid of strain, such as passive coastal margins, have predominantly isotropic topography with typically dendritic drainage network patterns. These methods can be used successfully to infer the settings of past or present tectonic regimes, and can be particularly useful in predicting the location and orientation of structural features that would otherwise be impossible to interpret in the field.

<gallery mode=packed-hover widths=1500px>
Image:Vario figures copy Page 01.png|''[[Topographic Anisotropy Figure 1|'''Figure 1''']]''|link=[[Topographic Anisotropy Figure 1]]
Image:Vario figures copy Page 02.png|''[[Topographic Anisotropy Figure 2|'''Figure 2''']]''|link=[[Topographic Anisotropy Figure 2]]
Image:Vario figures copy Page 03.png|''[[Topographic Anisotropy Figure 3|'''Figure 3''']]''|link=[[Topographic Anisotropy Figure 3]]
Image:Vario figures copy Page 04.png|''[[Topographic Anisotropy Figure 4|'''Figure 4''']]''|link=[[Topographic Anisotropy Figure 4]]
Image:Vario figures copy Page 05.png|''[[Topographic Anisotropy Figure 5|'''Figure 5''']]''|link=[[Topographic Anisotropy Figure 5]]
Image:Vario figures copy Page 06.png|''[[Topographic Anisotropy Figure 6|'''Figure 6''']]''|link=[[Topographic Anisotropy Figure 6]]
Image:Vario figures copy Page 07.png|''[[Topographic Anisotropy Figure 7|'''Figure 7''']]''|link=[[Topographic Anisotropy Figure 7]]
Image:Vario figures copy Page 08.png|''[[Topographic Anisotropy Figure 8|'''Figure 8''']]''|link=[[Topographic Anisotropy Figure 8]]
Image:Vario figures copy Page 09.png|''[[Topographic Anisotropy Figure 9|'''Figure 9''']]''|link=[[Topographic Anisotropy Figure 9]]
Image:Vario figures copy Page 10.png|''[[Topographic Anisotropy Figure 10|'''Figure 10''']]''|link=[[Topographic Anisotropy Figure 10]]
</gallery>

Connections between rock mass strength and grain size in alluvium

2016-02-18T01:15:03Z

Sam:

'''The sensitivity of fluvial erosion to rock damage'''

Roy, S.G.; Tucker, G.E.; Koons, P.O.; Smith, S.M.; Upton, P.

'''0. Abstract'''

We explore two ways in which the mechanical properties of rock potentially influence fluvial incision and sediment transport within a watershed: 1) rock erodibility is inversely proportional to rock cohesion, and 2) fracture spacing influences the initial grain sizes produced upon erosion. Fault weak zones show these effects particularly well because of the sharp cohesion and fracture spacing gradients associated with localized shear abrasion. A natural example of fault erosion is used to motivate our calibration of a generalized landscape evolution model. A suite of numerical experiments are used to study the sensitivity of river erosion and transport processes to variable degrees of rock weakening. In the experiments, rapid erosion and transport of fault gouge steers surface runoff, causing high order channels to become confined within the structure of weak zones. Erosion of adjacent, intact bedrock produces relatively coarser grained gravels that accumulate in the low relief of the eroded weak zone. The thickness and residence time of sediments stored there depends on the relief of the valley, which in these models is dependent on the degree of rock weakening. The frequency at which the weak zone is armored by bedload increases with greater weakening, causing the bedload to control local channel slope rather than the intermittently exposed bedrock. Conversely, small tributaries feeding into the weak zone are predominantly detachment-limited. The prevalence of features that impose mechanical heterogeneity on the Earth’s surface exert significant controls on the rates and patterns of erosion, and it will be important to recognize the role of heterogeneity in future landscape evolution studies.

[[File:2015JF003662-f01.png|500px|thumb|left|Henry Saddle: natural example of fault erosion.]]

[[File:2015JF003662-f04.png|500px|thumb|left|Channel profile model solution of mixed sand-gravel alluvium transport, bedrock incision.]]

[[File:texture_figures-03.jpg|500px|thumb|left|Experimental results of fault erosion. Greater fault damage leads to alignment of high order channel to fault strike, greater accumulation of coarse grained sediments.]]

Connections between rock mass strength and grain size in alluvium

2016-02-18T01:13:15Z

Sam:

File:2015JF003662-f04.png

2016-02-18T01:11:56Z

Sam: Sam uploaded a new version of File:2015JF003662-f04.png

File:2015JF003662-f04.png

2016-02-18T01:11:05Z

Sam:

File:2015JF003662-f01.png

2016-02-18T01:09:29Z

Sam:

Connections between rock mass strength and grain size in alluvium

2016-02-18T01:07:25Z

Sam:

'''The sensitivity of fluvial erosion to rock damage'''

Roy, S.G.; Tucker, G.E.; Koons, P.O.; Smith, S.M.; Upton, P.

'''0. Abstract'''

We explore two ways in which the mechanical properties of rock potentially influence fluvial incision and sediment transport within a watershed: 1) rock erodibility is inversely proportional to rock cohesion, and 2) fracture spacing influences the initial grain sizes produced upon erosion. Fault weak zones show these effects particularly well because of the sharp cohesion and fracture spacing gradients associated with localized shear abrasion. A natural example of fault erosion is used to motivate our calibration of a generalized landscape evolution model. A suite of numerical experiments are used to study the sensitivity of river erosion and transport processes to variable degrees of rock weakening. In the experiments, rapid erosion and transport of fault gouge steers surface runoff, causing high order channels to become confined within the structure of weak zones. Erosion of adjacent, intact bedrock produces relatively coarser grained gravels that accumulate in the low relief of the eroded weak zone. The thickness and residence time of sediments stored there depends on the relief of the valley, which in these models is dependent on the degree of rock weakening. The frequency at which the weak zone is armored by bedload increases with greater weakening, causing the bedload to control local channel slope rather than the intermittently exposed bedrock. Conversely, small tributaries feeding into the weak zone are predominantly detachment-limited. The prevalence of features that impose mechanical heterogeneity on the Earth’s surface exert significant controls on the rates and patterns of erosion, and it will be important to recognize the role of heterogeneity in future landscape evolution studies.

[[File:2015JF003662-f01.png|500px|thumb|left|Henry Saddle: natural example of fault erosion.]]

[[File:2015JF003662-f04.png|500px|thumb|left|1-D solution of mixed sand-gravel alluvium transport, bedrock incision.]]

[[File:texture_figures-03.jpg|500px|thumb|left|Experimental results of fault erosion.]]

University of Maine SECS Numerical Laboratory

2016-02-18T00:57:58Z

Sam:

'''Welcome to UMaine Geodynamics!'''

This wiki is a means for accessing research and educational modules produced by the geodynamics group at UMaine.
Follow links on the navigation pane to the left to search through our various research projects.

[[New Results|News:]]

2/17/15: Sam Roy made revisions to [[Tectonic-Geomorphic-Climatic Interaction (NSF-EAR-1324637, 1323137)]]

[[File:itsonlyamodel.png]]

(http://www.funnyjunk.com/)

10/28/15: An "Events" section has been added to the sidebar in anticipation of the upcoming GeoPRISMS collaborative session at UMaine. Participants can find session announcements and links to PDFs on the [[GeoPRISMS Workshop 2015]] page.

10/1/15: Lynn Kaluzienski created "[[Smoothed Particle Hydrodynamics|Smoothed Particle Hydrodynamics]]," complete with model descriptions and animations.
{| class="wikitable"
|-
![[File:Periodic Boundary Conditions-1.gif|700px|thumb|link=Smoothed Particle Hydrodynamics]]
|}

9/17/15: Sam Roy updated text and model results in [[Subduction Zone Dynamics in the Mantle and at the Earth's Surface]]:
{| class="wikitable"
|-
![[File:Vel1.gif|500px|thumb]]
|}

5/26/15: fault motion and landscape evolution model results have been updated: [[The role of surface displacement in landscape evolution]]

3/26/15: Sam Roy added modeling work on Mantle Wedge Hydration under "Previous Research": [[Mantle Wedge Hydration]]

3/18/15: Sam Roy and Nick Richmond have been running coupled FLAC/CHILD models to investigate orographic precipitation. Stay tuned!

Consult the [//meta.wikimedia.org/wiki/Help:Contents User's Guide] for information on using the wiki software.

== Getting started ==
* [//www.mediawiki.org/wiki/Manual:Configuration_settings Configuration settings list]
* [//www.mediawiki.org/wiki/Manual:FAQ MediaWiki FAQ]
* [https://lists.wikimedia.org/mailman/listinfo/mediawiki-announce MediaWiki release mailing list]

University of Maine SECS Numerical Laboratory

2016-02-18T00:56:11Z

Sam:

'''Welcome to UMaine Geodynamics!'''

This wiki is a means for accessing research and educational modules produced by the geodynamics group at UMaine.
Follow links on the navigation pane to the left to search through our various research projects.

[[New Results|News:]]

2/17/15: Sam Roy made revisions to [[Tectonic-Geomorphic-Climatic Interaction (NSF-EAR-1324637, 1323137)]]

[[File:itsonlyamodel.png]]
copyright Monty Python

10/28/15: An "Events" section has been added to the sidebar in anticipation of the upcoming GeoPRISMS collaborative session at UMaine. Participants can find session announcements and links to PDFs on the [[GeoPRISMS Workshop 2015]] page.

10/1/15: Lynn Kaluzienski created "[[Smoothed Particle Hydrodynamics|Smoothed Particle Hydrodynamics]]," complete with model descriptions and animations.
{| class="wikitable"
|-
![[File:Periodic Boundary Conditions-1.gif|700px|thumb|link=Smoothed Particle Hydrodynamics]]
|}

9/17/15: Sam Roy updated text and model results in [[Subduction Zone Dynamics in the Mantle and at the Earth's Surface]]:
{| class="wikitable"
|-
![[File:Vel1.gif|500px|thumb]]
|}

5/26/15: fault motion and landscape evolution model results have been updated: [[The role of surface displacement in landscape evolution]]

3/26/15: Sam Roy added modeling work on Mantle Wedge Hydration under "Previous Research": [[Mantle Wedge Hydration]]

3/18/15: Sam Roy and Nick Richmond have been running coupled FLAC/CHILD models to investigate orographic precipitation. Stay tuned!

Consult the [//meta.wikimedia.org/wiki/Help:Contents User's Guide] for information on using the wiki software.

== Getting started ==
* [//www.mediawiki.org/wiki/Manual:Configuration_settings Configuration settings list]
* [//www.mediawiki.org/wiki/Manual:FAQ MediaWiki FAQ]
* [https://lists.wikimedia.org/mailman/listinfo/mediawiki-announce MediaWiki release mailing list]

University of Maine SECS Numerical Laboratory

2016-02-18T00:55:40Z

Sam:

'''Welcome to UMaine Geodynamics!'''

This wiki is a means for accessing research and educational modules produced by the geodynamics group at UMaine.
Follow links on the navigation pane to the left to search through our various research projects.

[[New Results|News:]]

2/17/15: Sam Roy made revisions to [[Tectonic-Geomorphic-Climatic Interaction (NSF-EAR-1324637, 1323137)]]

[[File:itsonlyamodel.png]]

copyright Monty Python

10/28/15: An "Events" section has been added to the sidebar in anticipation of the upcoming GeoPRISMS collaborative session at UMaine. Participants can find session announcements and links to PDFs on the [[GeoPRISMS Workshop 2015]] page.

10/1/15: Lynn Kaluzienski created "[[Smoothed Particle Hydrodynamics|Smoothed Particle Hydrodynamics]]," complete with model descriptions and animations.
{| class="wikitable"
|-
![[File:Periodic Boundary Conditions-1.gif|700px|thumb|link=Smoothed Particle Hydrodynamics]]
|}

9/17/15: Sam Roy updated text and model results in [[Subduction Zone Dynamics in the Mantle and at the Earth's Surface]]:
{| class="wikitable"
|-
![[File:Vel1.gif|500px|thumb]]
|}

5/26/15: fault motion and landscape evolution model results have been updated: [[The role of surface displacement in landscape evolution]]

3/26/15: Sam Roy added modeling work on Mantle Wedge Hydration under "Previous Research": [[Mantle Wedge Hydration]]

3/18/15: Sam Roy and Nick Richmond have been running coupled FLAC/CHILD models to investigate orographic precipitation. Stay tuned!

Consult the [//meta.wikimedia.org/wiki/Help:Contents User's Guide] for information on using the wiki software.

== Getting started ==
* [//www.mediawiki.org/wiki/Manual:Configuration_settings Configuration settings list]
* [//www.mediawiki.org/wiki/Manual:FAQ MediaWiki FAQ]
* [https://lists.wikimedia.org/mailman/listinfo/mediawiki-announce MediaWiki release mailing list]

University of Maine SECS Numerical Laboratory

2016-02-18T00:54:30Z

Sam:

'''Welcome to UMaine Geodynamics!'''

This wiki is a means for accessing research and educational modules produced by the geodynamics group at UMaine.
Follow links on the navigation pane to the left to search through our various research projects.

[[New Results|News:]]
2/17/15: Sam Roy made revisions to [[Tectonic-Geomorphic-Climatic Interaction (NSF-EAR-1324637, 1323137)]]

10/28/15: An "Events" section has been added to the sidebar in anticipation of the upcoming GeoPRISMS collaborative session at UMaine. Participants can find session announcements and links to PDFs on the [[GeoPRISMS Workshop 2015]] page.

10/1/15: Lynn Kaluzienski created "[[Smoothed Particle Hydrodynamics|Smoothed Particle Hydrodynamics]]," complete with model descriptions and animations.
{| class="wikitable"
|-
![[File:Periodic Boundary Conditions-1.gif|700px|thumb|link=Smoothed Particle Hydrodynamics]]
|}

9/17/15: Sam Roy updated text and model results in [[Subduction Zone Dynamics in the Mantle and at the Earth's Surface]]:
{| class="wikitable"
|-
![[File:Vel1.gif|500px|thumb]]
|}

5/26/15: fault motion and landscape evolution model results have been updated: [[The role of surface displacement in landscape evolution]]

3/26/15: Sam Roy added modeling work on Mantle Wedge Hydration under "Previous Research": [[Mantle Wedge Hydration]]

3/18/15: Sam Roy and Nick Richmond have been running coupled FLAC/CHILD models to investigate orographic precipitation. Stay tuned!

Consult the [//meta.wikimedia.org/wiki/Help:Contents User's Guide] for information on using the wiki software.

== Getting started ==
* [//www.mediawiki.org/wiki/Manual:Configuration_settings Configuration settings list]
* [//www.mediawiki.org/wiki/Manual:FAQ MediaWiki FAQ]
* [https://lists.wikimedia.org/mailman/listinfo/mediawiki-announce MediaWiki release mailing list]

University of Maine SECS Numerical Laboratory

2016-02-18T00:53:56Z

Sam:

'''Welcome to UMaine Geodynamics!'''

This wiki is a means for accessing research and educational modules produced by the geodynamics group at UMaine.
Follow links on the navigation pane to the left to search through our various research projects.

[[New Results|News:]]
2/17/15: Sam Roy made revisions to [[Tectonic-Geomorphic-Climatic Interaction]]

10/28/15: An "Events" section has been added to the sidebar in anticipation of the upcoming GeoPRISMS collaborative session at UMaine. Participants can find session announcements and links to PDFs on the [[GeoPRISMS Workshop 2015]] page.

10/1/15: Lynn Kaluzienski created "[[Smoothed Particle Hydrodynamics|Smoothed Particle Hydrodynamics]]," complete with model descriptions and animations.
{| class="wikitable"
|-
![[File:Periodic Boundary Conditions-1.gif|700px|thumb|link=Smoothed Particle Hydrodynamics]]
|}

9/17/15: Sam Roy updated text and model results in [[Subduction Zone Dynamics in the Mantle and at the Earth's Surface]]:
{| class="wikitable"
|-
![[File:Vel1.gif|500px|thumb]]
|}

5/26/15: fault motion and landscape evolution model results have been updated: [[The role of surface displacement in landscape evolution]]

3/26/15: Sam Roy added modeling work on Mantle Wedge Hydration under "Previous Research": [[Mantle Wedge Hydration]]

3/18/15: Sam Roy and Nick Richmond have been running coupled FLAC/CHILD models to investigate orographic precipitation. Stay tuned!

Consult the [//meta.wikimedia.org/wiki/Help:Contents User's Guide] for information on using the wiki software.

== Getting started ==
* [//www.mediawiki.org/wiki/Manual:Configuration_settings Configuration settings list]
* [//www.mediawiki.org/wiki/Manual:FAQ MediaWiki FAQ]
* [https://lists.wikimedia.org/mailman/listinfo/mediawiki-announce MediaWiki release mailing list]

The role of surface displacement in landscape evolution

2016-02-18T00:50:34Z

Sam:

<div style="font-size:120%">
The objective of this project is to study the effects of 3D fault slip on landscape evolution. Specifically, there can be implications for the steepness of rivers and the evolution of drainage network patterns when considering the full 3D solution for fault slip. Our method is to apply kinematic conditions to points on a model landscape surface, representing tectonic motion, and allow for surface processes to erode the surface. Additionally we include rock damage associated with shear strain as an influence on rock erodibility surrounding the fault. Results suggest that the lateral motion attributed to slip along a fault plane can drastically increase channel slope in reverse thrust regimes and decrease slope in normal rift regimes, however, this depends on the dip angle of the primary slip surface.

Model results suggest three major ways in which rivers will align to fault structures:

1. Kinematic: Strike-slip motion displaces rivers that cross the primary slip surface, extending their reach along strike. The magnitude of this extension depends on the slip rate after a pseudo-steady-state is reached.

2. Kinematic: Dip-slip convergence advects channel sections toward the primary slip surface. Because the hanging wall is eroded before it can cross the current exposure of the fault strike, rivers continue to follow these channel sections that have been transferred to the primary slip surface.

3. Damage/Erosion: Local reductions in rock strength associated with continued shear abrasion enhances erodibility along fault strike, lading to rapid erosion rates and alignment of large channels to the primary slip surface.

Future work: This sensitivity analysis uses 3D kinematic solutions to predict what may happen under dynamic situations of tectonic deformation.
{| class="wikitable"
|-
! style="width:500px" | [[File:kin_slope-v-area.jpg|500px|thumb|Experimental models used to determine influence of lateral surface motion on surface slopes. (A) Block uplift, no lateral motion (black); (B) reverse dip-slip (red); (C) normal dip-slip (blue). (D) E-W topographic profiles. (E) Slope versus area log-log plots]]
|-
! style="width:500px" | [[File:kinematic-01.png|500px|thumb|left|Reverse dip-slip faulting]]
! {{#ev:youtube|epZmuzxnGk8}}
|-
! style="width:500px" | [[File:kinematic-02.png|500px|thumb|left|Normal dip-slip faulting]]
! {{#ev:youtube|V5803fcKFpY}}
|-
! style="width:500px" | [[File:kinematic-03.png|500px|thumb|left|Left-lateral strike-slip faulting]]
! {{#ev:youtube|U-7Ex4wSmmw}}
|-
! style="width:500px" | [[File:kinematic-04.png|500px|thumb|left|Reverse oblique-slip faulting]]
! {{#ev:youtube|XVPzurj9TRE}}
|}
</div>
Images and models produced by Sam Roy

The role of surface displacement in landscape evolution

2016-02-18T00:50:06Z

Sam:

<div style="font-size:150%">
The objective of this project is to study the effects of 3D fault slip on landscape evolution. Specifically, there can be implications for the steepness of rivers and the evolution of drainage network patterns when considering the full 3D solution for fault slip. Our method is to apply kinematic conditions to points on a model landscape surface, representing tectonic motion, and allow for surface processes to erode the surface. Additionally we include rock damage associated with shear strain as an influence on rock erodibility surrounding the fault. Results suggest that the lateral motion attributed to slip along a fault plane can drastically increase channel slope in reverse thrust regimes and decrease slope in normal rift regimes, however, this depends on the dip angle of the primary slip surface.

Model results suggest three major ways in which rivers will align to fault structures:

1. Kinematic: Strike-slip motion displaces rivers that cross the primary slip surface, extending their reach along strike. The magnitude of this extension depends on the slip rate after a pseudo-steady-state is reached.

2. Kinematic: Dip-slip convergence advects channel sections toward the primary slip surface. Because the hanging wall is eroded before it can cross the current exposure of the fault strike, rivers continue to follow these channel sections that have been transferred to the primary slip surface.

3. Damage/Erosion: Local reductions in rock strength associated with continued shear abrasion enhances erodibility along fault strike, lading to rapid erosion rates and alignment of large channels to the primary slip surface.

Future work: This sensitivity analysis uses 3D kinematic solutions to predict what may happen under dynamic situations of tectonic deformation.
{| class="wikitable"
|-
! style="width:500px" | [[File:kin_slope-v-area.jpg|500px|thumb|Experimental models used to determine influence of lateral surface motion on surface slopes. (A) Block uplift, no lateral motion (black); (B) reverse dip-slip (red); (C) normal dip-slip (blue). (D) E-W topographic profiles. (E) Slope versus area log-log plots]]
|-
! style="width:500px" | [[File:kinematic-01.png|500px|thumb|left|Reverse dip-slip faulting]]
! {{#ev:youtube|epZmuzxnGk8}}
|-
! style="width:500px" | [[File:kinematic-02.png|500px|thumb|left|Normal dip-slip faulting]]
! {{#ev:youtube|V5803fcKFpY}}
|-
! style="width:500px" | [[File:kinematic-03.png|500px|thumb|left|Left-lateral strike-slip faulting]]
! {{#ev:youtube|U-7Ex4wSmmw}}
|-
! style="width:500px" | [[File:kinematic-04.png|500px|thumb|left|Reverse oblique-slip faulting]]
! {{#ev:youtube|XVPzurj9TRE}}
|}
</div>
Images and models produced by Sam Roy

File:Founderplot.png

2015-09-19T00:44:38Z

Sam:

File:Founder.gif

2015-09-19T00:44:14Z

Sam:

Subduction Zone Dynamics in the Mantle and at the Earth's Surface

2015-09-19T00:43:29Z

Sam:

<div style="font-size:150%">

'''Subduction zone dynamics in the mantle and at Earth's surface'''

An educational module for the University of Maine School of Earth and Climate Sciences courses in Geophysics and Fluid Dynamics

Created by Sam Roy (Samuel.g.roy@maine.edu) on 4/28/2012
Last edited on 8/2015

{| class="wikitable"
|-
! style="width:500px" | [[File:aleutian.png|500px|thumb]]
! style="width:500px" | [[File:Vel1.gif|500px|thumb]]
|-
! Figure 1: The center of the Aleutian Megathrust:

a major subduction zone of massive scale.
! Animation 1: 2D numerical model of slab subduction.

Velocity magnitude, 1022 Pa s lithosphere.

Arrows denote flow orientation.
|}

'''Two main hypotheses to explore:'''

1. Mantle advection controls surface deformation through mechanical coupling of lithosphere and asthenosphere.

2. The lithosphere is non-Newtonian and exhibits strain weakening behavior, this can lead to strain localization and slab detachment. Strain rate is normally greatest in the subduction hinge therefore weakening and detachment would probably occur there.

'''1. Introduction: '''
The surface of the Earth takes many varying shapes, from high craggy peaks and steep gorges to rolling hills and flat coastal plains. But how and why does the Earth's surface takes its form? There are many processes that play an active role in the creation of topography and landforms, but in this module we will explore the role of mantle advection as the primary mechanism behind surface deformation (Figure 1). First, I will discuss our physical understanding of mantle dynamics, then we will use a physical model to explore the sensitivity of surface shape to various rheological conditions in the lithosphere and underlying mantle.

'''2. Physics'''
A thorough understanding of surface deformation requires a thorough study of the coupling between lithosphere and the underlying mantle. We will apply the Navier-Stokes equation to define fluid movement in the Earth. For our purposes, let’s approximate the rheological properties of the lithosphere and mantle as high viscosity, incompressible fluids with no elasticity. This means that we assume the elastic and plastic properties of the lithosphere are insignificant and volumetrically dominated by the viscous behavior below, at least for the large spatial scales and long timescales we are interested in. I will now go into more detail on the derivation of Navier-Stokes, the basic equation used to define fluid flow.

'''2.1. Navier-Stokes derivation'''
How is the Earth like a fluid? Fluids are able to flow, or internally deform, when a force is applied on them. Below its frictional exterior, the Earth can readily be defined as a high viscosity fluid. This force can take the form of a loading stress, where the fluid experiences pressure due to the loading of more fluid above it

(1) P = ρ g h sin(α)

where ρ is density of the fluid, g is acceleration due to gravity, h is the height of the overlying fluid, and α is the angle of the fluid surface. If the fluid boundary is not horizontal, a pressure gradient exists until the fluid deforms to once again create a horizontal surface. This deformation is opposed by the dynamic viscosity of the fluid, defined mathematically as

(2) μ = σ / εij , εij = ∂vi / ∂ j

where μ is viscosity, σ is the stress initiated by gravitational acceleration, and εij is shear strain rate, or the change in i velocity in direction j. This equation holds true for Newtonian materials, which maintain a constant viscosity regardless of a change in strain rate. If we consider equation 1 as a component driving fluid flow, and equation 2 as a component resisting fluid flow, the two will equal each other if the fluid is in a kinematic steady state:

(3) ρ g h sin(α) = μ εij

We then take the partial derivative with respect to distance of both sides to establish that this relationship is true for a gradient ∇ in all considered dimensions

(4) ∇P = μ ∇ε , ∇ = ∂ / ∂i + ∂ / ∂j + ∂ / ∂k

Notice that I do not take the partial derivative of viscosity because it is considered to be a constant here. Now we can consider a volume force established by the presence of more than one fluid with different viscosities. A fluid that is more dense than a surrounding fluid wants to sink, and it will accelerate downward until there is great enough viscosity resistance to maintain a constant, terminal velocity. The complete Navier-Stokes formula is thus

(5) ∆ρ ∂v / ∂t = ∆ ρ g - ∇P + μ ∇ε

where ∆ρg is a volume force dependent on the density difference between two fluids, and ∆ρ ∂v / ∂t is the potential acceleration of the fluid body if resisting and driving forces do not equilibrate. This equation is simple, yet it defines the behavior of all non-turbulent fluid flow. In this present form we can use Navier-Stokes to consider the problem of fluid flow as gradients across a finite element continuum in two or three dimensions, discussed further below.

'''2.2. Temperature dependencies for density and viscosity'''
The mantle and lithosphere are almost continuously coupled over Earth's entirety, therefore any differential movement in the mantle can produce deformation at the surface. Both mantle and crust can be considered as highly viscous fluids, and both fluid and density are temperature dependent. This is validated by the fact that brittle rock behavior normally occurs only within the first 15 km of crust, at which depth temperatures are conducive to dislocation creep of quartz, the most abundant upper crustal mineral. The Earth's density gradient between lithosphere and asthenosphere is established by the thermal gradient produced by radioactive decay of Uranium, Thorium, their daughter products, and mantle advection. Density is linked to temperature by the phenomenological volumetric expansion of heated material

(6) ρ = ρo - αv ∆T

where ∆T is the amount of temperature change (T2-T1) experienced by the material, ρo is the original density before the change in temperature, and αv is the material specific volumetric coefficient of thermal expansion. Unlike the decrease in density with decreasing temperature caused by the phase change in water, leading to buoyant ice floating atop liquid water, rock only becomes more dense as it cools. As a result there is a density instability initiated within the upper mantle. This density instability provides a negative buoyancy force that can drive advection between the lithosphere and the rest of the mantle.
A temperature rise also increases the agitation of molecular bonds in a material, and for a fluid, this causes a reduction in viscosity. Molecular agitation is opposed by confining pressures, but there is a range within the upper mantle where the effect of temperature on viscosity exceeds the confining pressure, and viscosity is greatly reduced at this depth. This weak zone of the mantle, known as the asthenosphere, holds the low viscosity condition that can allow the negative buoyancy force of the lithosphere to initiate downward advection of materials.
Strain can reduce the viscosity of the material where advection is greatest for a non-Newtonian fluid, therefore a nonlinear relationship exists between the stress produced by the buoyancy force and the strain rate produced by it. Localized weakening of the lithosphere can lead to breakoff of the slab in particularly strained locations.

'''2.3 Non-Newtonian fluids'''
I previously defined Newtonian fluids as those that maintain a constant viscosity regardless of the strain rate acting upon them. Non-Newtonian fluids do not hold to this constraint and viscosity will change with any change in strain rate according to the equation

(7) σn = μ ∇ε

where n is the stress exponent value that emplaces a nonlinear, power law dependency on viscosity. Most Earth materials are strain weakening, meaning that viscosity decreases with higher shear strain rate when n> 1. Some materials, such as partially crystallized magmas, fluidized corn starch, or any fluid containing suspended solids, are strain hardening, and viscosity increases with increasing shear strain rate, represented by n<1. My subduction model explores deformation patterns for Newtonian and strain weakening lithosphere.

'''3. Methods'''

I use a numerical model to explore the link between surface deformation and mantle advection for a dominantly 2D subduction zone (Figure 2), such as the Aleutian Megathrust of Alaska. The model is a finite element, 2D, transient treatment of the Navier-Stokes equation. Fluid flow is supplemented by an alternating Lagrangian-Eularian reference frame (ALE) that allows physical deformation of the domain mesh based on velocity inputs from the Navier-Stokes solution. Materials are incompressible and momentum and mass are conserved. The mesh is triangular and is able to reconfigure its shape and resolution once an element quality threshold is met (Figure 3). Element quality is a measurement of how stretched the triangle has become due to strain; elements that diverge from an equilateral geometry will have a low element quality. The geometric extent of the domains is meant to replicate two large converging plates overlying a column of mantle that extends to the outer core.

{| class="wikitable"
|-
! style="width:500px" | [[File:2dsubgrid.png|500px|thumb|Figure 2: Geometry and mesh of the numerical model. Subduction angle is set to 30 degrees.]]
! style="width:300px" | [[File:meshqual.png|300px|thumb|Figure 3: Plot of mesh quality after the domains have sustained large strains. Red elements = high quality, blue = low quality.]]
|}

Density and viscosity values are chosen based on composition and initial temperature. however I do not incorporate dynamic temperature (Figure 4). A density difference of 50 kg m-3 exists between the mantle lithosphere and the underlying mantle, and the volumetric contribution from oceanic and continental crust slightly reduces this difference. The first model simulations assume that all materials are Newtonian, therefore dynamic viscosity is constant regardless of strain rate. Later models incorporate strain weakening in the lithosphere, and all models have a viscosity gradient in the upper mantle.
The walls and base of the mantle are closed to all normal velocity and deformation but allow lateral movement, and the top layer imposes a normal boundary stress equal to atmospheric pressure, to replicate the surface of the Earth (Figure 5). The left boundary of the lithosphere has a normal velocity of 10 mm a-1 to replicate a far field plate velocity.

{| class="wikitable"
|-
! style="width:300px" | [[File:densvisc.png|300px|thumb|Figure 4: Density (left) and viscosity (right) distributions. Mantle lithosphere density: 3300 kg m-3, mantle density: 3250 kg m-3, continental and oceanic crust: 2700 and 3000 kg m-3. Viscosity gradient spans 5x1019 Pa s to 3x1021 Pa s at 660 km phase discontinuity.]]
! style="width:500px" | [[File:2dsubbounds.png|500px|thumb|Figure 5: Boundary conditions: Interior domains and boundaries: free deformation by Navier-Stokes module. Red boundaries: closed to normal velocities/displacements. Yellow boundary: normal velocity of 10 mm a-1 imposed. Green boundary: normal stress load equal to atmospheric pressure.]]
|}
'''4. Results and Discussion'''

'''4.1. Newtonian Lithosphere'''
Animations 1-4 display modeled velocity magnitude, normal y axis strain rates, normal x axis strain rates, and vorticity magnitude results for a Newtonian lithosphere undergoing deformation along a subducting trench for approximately 10 Ma. The negative buoyancy of the lithosphere is enough to overcome the resistance of viscosity and subduction commences. The hinge zone, or the zone where the lithosphere angles downward, rotates to accommodate a steepening angle as the slab sinks quickest from its center of mass. The mantle reacts to the sinking slab and convection cells are established along either side of the sinking slab. Mantle convection introduces a lateral velocity that, given traction to a coupled lithosphere, causes convergence just above the subducting slab, best seen in Animation 3. This zone above the subducting slab is also extended vertically, best seen in Animation 2, and the contribution of horizontal shortening and vertical extension allows a fraction of upward deformation at the surface boundary, creating topography (Animation 5-6). Deformation is dominated by the subducting slab, and any contribution from the far field plate velocity is of a lower magnitude.
I reduced the viscosity slightly for a second simulation (Animation 7-9) to display the importance of this resisting component. The lithosphere quickly subducts and deforms into a "fish hook" geometry over a much shorter time scale, but also the surface topography is greatly perturbed by rapid uplift rates. A non-Newtonian model should exemplify rapid deformation for low viscosity, weakened areas, while maintaining high viscosity regions that experience little shear strain.

{| class="wikitable"
|-
! style="width:500px" | [[File:Vel1.gif|500px|thumb|Animation 1: 2D numerical model of slab subduction. Velocity magnitude, 1022 Pa s lithosphere. Arrows denote flow orientation.]]
! style="width:500px" | [[File:eyy1.gif|500px|thumb|Animation 2: Normal strain along the vertical axis, 1022 Pa s lithosphere. Arrows display y velocity component only.]]
|-
! style="width:500px" | [[File:exx1.gif|500px|thumb|Animation 3: Normal strain along the horizontal axis, 1022 Pa s lithosphere. Arrows display x velocity component only.]]
! style="width:500px" | [[File:vort1.gif|500px|thumb|Animation 4: Vorticity magnitude, 1022 Pa s lithosphere. Arrows denote flow orientation.]]
|-
! style="width:500px" | [[File:topo1.gif|500px|thumb|Animation 5: Surface elevation, 1022 Pa s lithosphere.]]
! style="width:500px" | [[File:urate1.gif|500px|thumb|Animation 6: Surface uplift rate, 1022 Pa s lithosphere.]]
|}

{| class="wikitable"
|-
! style="width:500px" | [[File:vel2.gif|500px|thumb|Animation 7: Surface elevation, 9.9x1021 Pa s lithosphere.]]
|-
! style="width:500px" | [[File:topo2.gif|500px|thumb|Animation 8: Surface elevation, 9.9x1021 Pa s lithosphere.]]
|-
! style="width:500px" | [[File:urate2.gif|500px|thumb|Animation 9: Surface uplift rate, 9.9x1021 Pa s lithosphere.]]
|}

'''4.2. Non-Newtonian Lithosphere'''
Figure 6 and Animation 10 display characteristic behavior of a weakly non-Newtonian lithosphere. The simulation shows the locations where we would expect shear strain weakening, namely along a dip where one would expect a reverse fault to exist. I do not incorporate an internal slip wall on this domain boundary because the geometry is too complex to approach convergence for any useful timestep, but you can see in Animation 10 that the shear strain localization fades away over time because the strain weakening isn't enough to allow effective localization to maintain an active fault zone. As the subducting slab begins to neck, strain weakening exists in the thinnest part. This could be the location where slab decoupling occurs. In the next results section I manually alter the model geometry to initiate the decoupling of the slab at this location to determine what effects would arise at the Earth's surface.
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! style="width:500px" | [[File:nnewt.png|500px|thumb|Figure 6: Dynamic viscosity for non-Newtonian lithosphere; before (left) and after (right) decoupling. Dark regions are weakened and have lower viscosity.]]
! style="width:500px" | [[File:nnewt.gif|500px|thumb|Animation 10: Deformation of a non-Newtonian viscosity lithosphere.]]
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4.3. Slab Decoupling and Surface Uplift
Figure 6 displays the condition of viscosity before and after the slab is decoupled. Animation 11 displays the normal vertical strain rate. The overlying lithosphere is still influenced by the foundering slab, but the gap that separates the two widens with each time step. This means that downward extension of the overlying lithosphere is reduced, and it is apparent from Figure 7 that a large proportion of this vertical extension is directed upward, to the surface. In reality, the rapid uplift would trigger nonlinear feedbacks with surface erosion, and a great deal of lithospheric exhumation would occur, exposing deeper parts of the lithosphere at the surface, possibly including ultra-high pressure metamorphic assemblages to surface. Existence of these high pressure assemblages would require a rapid mechanism of uplift such as from this decoupling slab model.
{| class="wikitable"
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! style="width:500px" | [[File:founder.gif|500px|thumb|Animation 11: vertical normal strain rate after slab decouples. Red denotes vertical extension, blue denotes compression.]]
! style="width:500px" | [[File:founderplot.png|500px|thumb|Figure 7: Surface topography and uplift rate (inset) before (blue) and after (green) the slab decouples.]]
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5. Summary and Conclusions
The model presented here depicts a simple 2D subduction zone analogous to the Aleutian Megathrust in Alaska. the model simulates the deformation of the subducting lithosphere, the mantle, and the surface of the Earth, and deformation is predominantly driven by the negative buoyancy of the overlying lithospheric mantle, just above the Asthenosphere. Subduction is successful because the negative buoyancy of the lithosphere successfully opposes the resistant viscosity of the mantle and the lithosphere. Viscosity is the only component that resists flow in this model, and any small fluctuation (on the order of 1020 Pa s) can lead to large changes in strain rate.
This model is greatly limited by an independence from a dynamic thermal gradient. Density and viscosity are based on the initial thermal gradient before subduction is initiated, but this pattern is quickly perturbed with consequences for material properties. This limitation is especially critical because model simulations typically run up to 10 Ma, which should be more than enough time to heat up a 150-200 km thick slab of lithosphere. Although many subduction zones can be largely defined in 2D, there can always be some influence in 3D that cannot be replicated by this model. This is especially true for subduction zones close to plate corners, bends in the subduction zone, lateral changes in lithosphere strength, or the existence of other foundering slabs that can incur 3D influences on an otherwise 2D system. There is no frictional behavior in this model, and no faults are established. This limitation is more important for crustal deformation, which is volumetrically only a very small component of the model, but I am concerned with surface deformation and in reality, the surface would be a frictional material, not a fluid. The model requires a higher magnitude constraint on non-Newtonian behavior to make it a truly high viscosity shear strain weakening material. Currently I can only pinpoint locations where weakening and localization would occur and initiate only small changes in dynamic viscosity, and I used this information to determine the location of slab decoupling as it is impossible for the model to decouple the slab itself. Finally, no surface mass transfer processes are employed in this model, but I would expect that higher uplift would cause a nonlinear feedback for higher erosion rates.

In conclusion, Subduction zones are thermo-gravitational systems that rely upon a thermal gradient to establish density and viscosity gradients to drive deformation. My fluid model simplifies the lithosphere and mantle and successfully replicates deformation within a subduction zone, and it can be used to determine the mechanics required in the mantle to cause uplift at the earth's surface. Substantial uplift will occur for a convergent zone with continental crust. Reduced strength in the lithosphere will amplify the rate of uplift, and decoupling of the foundering slab will also increase uplift rates potentially spanning millions of years.

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