Soil Geomorphology

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Soil Geomorphology
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The geomorphic surface -definable in space and
time
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Slope effects on soils 1. sediment transfer 2.
water table effects
Water table
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Catena predictable series of soils on a slope
Each pedon on the slope is linked to the one
upslope and downslope, via sediment transfer
and water table relationships
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Wetter, cooler, more OM preserved
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Categorizing surfaces (dating comes later)
A. isochronous vs time-transgressive B. subaerial
vs subaqueous C. constructional/depositional vs
erosional D. stable vs unstable
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Floodplain surface - isochronous
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Terrace surfaces also isochronous
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Downcutting and meandering river forms a
time-transgressive surface
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Categorizing surfaces (dating comes later)
A. isochronous vs time-transgressive B. subaerial
vs subaqueous C. constructional/depositional vs
erosional D. stable vs unstable
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Categorizing surfaces (dating comes later)
A. isochronous vs time-transgressive B. subaerial
vs subaqueous C. stable vs unstable
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Unstable!
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Unstable!
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Stable
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Slope STABILITY (or the type and degree of
INSTABILITY) best determined by soils data
Soils should be better developed here
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Categorizing surfaces (dating comes later)
A. isochronous vs time-transgressive B. subaerial
vs subaqueous C. stable vs unstable D.
constructional/depositional vs erosional
Degradational
Aggradational
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CUMULIZATION
Thin soils on backslopes
Cumulic (potentially) soils on foot and
toeslopes
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Cumulic soil in a swale on a prairie
landscape, Illinois
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Cumulization vs burial
Pedogenesis cannot keep pace with sediment
additions, profile gets buried Aka, retardant
upbuilding
A horizon thickens as new sediment is added aka,
developmental upbuilding
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Many times, the drainage class does not change
markedly along a slope, but the materials at
the base of the slope are colluvial in nature,
and thus are --pre-weathered before soil
genesis starts at their new location --more
weathered, now --finer textured
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Retardant upbuilding
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Cumulic soil on a floodplain
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Categorizing surfaces (dating comes later)
A. isochronous vs time-transgressive B. subaerial
vs subaqueous C. stable vs unstable D.
constructional/depositional vs erosional E.
convex vs concave
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Slope elements
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Thin soils on shoulder
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Entire soil profile intact on footslope
E horizon at surface (less erosion)
Eroded shoulder slope (Reddish B horizon peeking
through)
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Erosion most pronounced on steepest slopes and on
those with lowest infiltration capacities
Stability
Deposition and/or cumulization
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Slope stability f(runoff) Runoff f(slope
gradient, precip rate, infiltration capacity)
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Slope stability f(runoff) Runoff f(slope
gradient, precip rate, infiltration capacity)
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SANDS
OTHER TEXTURES
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SANDS
OTHER TEXTURES
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STABLE slopes --and heres how we know!
Rubicon on valley floor
Blue Lake on Finger uplands
Feldhauser on flattest Finger uplands
Kalkaska on steep (F) slopes on Finger sides
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Remember the gullies?
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Uplands always the driest sites, right?
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Water table deepest on uplands common setup
- driest soils on uplands
soil surface
water table
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When uplands are flat sites sites are on
shoulders
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Flat, loess-covered (silty clay loam) uplands in
S Illinois
VPD
PD
SPD
SPD
PD
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Same area, near incised valleys
PD
SPD
SPD
SPD
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Slopes in 2-d and 3-d
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In 2-d
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Morphometry of surface creates flows of energy,
water and matter. Most important morphometric
form is the catena (up and down the slope).
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Catena toposequence (sortof)
In theory, all one parent material
In theory, can be different parent materials
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Catena toposequence (sortof)
In theory, all one parent material
In theory, can be different parent materials
hydrosequence (sortof)
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Reasons for soil variation along a
catena wetness/soil moisture/water table
changes redistribution of sediment microclimate
WATER TABLE EFFECTS
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Reasons for soil variation along a
catena wetness/soil moisture/water table
changes redistribution of sediment microclimate
SLOPE EFFECTS
WATER TABLE EFFECTS
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Reasons for soil variation along a
catena wetness/soil moisture/water table
changes redistribution of sediment microclimate
SLOPE EFFECTS
WATER TABLE EFFECTS
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Things to consider about slopes and soils
1. Slope gradient (steepness)
A
B
C
D
E
F
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The 2 implies erosion has occurred
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Things to consider about slopes and soils
1. Slope gradient (steepness)
2. Slope length
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In 3-d
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Things to consider about slopes and soils
1. Slope gradient (steepness)
2. Slope length
3. Slope curvature
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Does the slope concentrate or diffuse overland
flow?
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Things to consider about slopes and soils
1. Slope gradient (steepness)
2. Slope length
3. Slope curvature
4. Slope aspect
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On NORTH slope
On SOUTH slope
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Soils on N and S slopes in the Alps, Italy
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Aspect where (at what latitudes)
is it most important?
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Aspect matters!
It primarily affects the energy and moisture
status of soils
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Driest, hottest slopes (N hemisphere) SW
Moistest, coolest slopes NE
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Shadowing is also important
shadow
shadow
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What should we expect re aspect and pedogenesis?
Depends on the energy and moisture needs and
limitations of the pedogenic processes on the
slopes.
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Examples On mesic sites with an abundance of
moisture, e.g., the Appalachians, energy may be
limiting for certain processes like weathering
and humification that depend on energy and
moisture.
Soils in such areas may exhibit increased
development on the warmer, south-facing slopes.
In these same areas, pedogenic processes that are
not as dependent upon energy but moreso upon
moisture (eluviation, podzolization, and
melanization) may be better expressed on cooler,
moister northern aspects.
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Examples
In pedogenically dry areas (dry with respect
to the amount of water that could be utilized
pedogenically), moisture may be limiting.
Here, the moister (poleward-facing) slope may
have better developed soils.
In cold, dry regions, energy may be more
pedogenically limiting than moisture. In
these areas S aspects may have the best developed
soils.
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The Palouse another example
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Uniform loess parent materials
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Plenty of snow in winter
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Driest sites, Soils have Bk horizons
Thick snow drifts, and addl water from runoff
- Have Bt horizons
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Microtopography
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Take the dam picture, already!
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Tree uprooting
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Uprooting on muck see the marl?
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Only 2-years old!
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24 years old (the girl, not the root plate)
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