Gradational processes
Weathering = breakdown of material in place
Tectonic processes build up of roughen up the earth
Gradational forces level off highs and fill in lows.
Gradation = leveling of land
degradation (erosion) = removal of highs
transportation = movement of material
aggradation (deposition) = filling in lows
Ultimate gradation --> level smooth plain at "base level"
base level ≈ sea level, cannot erode farther downward
Principal agents of gradation
gravity
water
wind
ice
Before material can be moved by any gradational agent,
it must be freed from its parent material or bedrock.
Landforms are usually result of more than one of these
Mountains do not move “en masse” to the sea
Breakdown of rock material in place = WEATHERING
Weathering does not, by itself, move material.
500 year old gargoyle
on the old well at the
National Museum of
the Middle Ages,
Paris
Three types of weathering
Physical
Chemical
Biological
Processes not mutually exclusive
one or the other may dominate due to climate
or rock type
1
Bedding planes, joints, fractures, make rock more
susceptible to weathering
Massive (non-jointed) rocks are slower to weather
Examples of Physical Weathering
1. Freezing water...expansion in cracks
most effective where daily freeze-thaw events
high elevations in mid-high latitudes
not very important in tropics or polar regions
Examples of Physical Weathering
3. Differential expansion
minerals expand and contract differently with
heat and cold
granite especially susceptible
fire promotes this
diurnal temperature changes may also be factor
Physical: makes smaller pieces from bigger pieces
does not change chemical composition of rock
disintegration
Important because
1. smaller pieces easier to move
2. increases surface area for chemical attack
Examples of Physical Weathering
2. Salt weathering...salt crystal expansion
capillary water evaporates leaving salt behind
sandstone especially susceptible
action similar to frost wedging
arid and semi arid regions
Examples of Physical Weathering
4. Unloading...removing pressure of overlying rock
exfoliation...peeling of thick concentric layers
common in granite
(unloading causes rock bursts in mines)
Causes peeling
of thin
concentric
shells
Half-dome in Yosemite 
2
Exfoliation
Evidence of physical weathering
Domes
Angular debris and jagged forms
Talus slopes (piles of broken rock)
Above tree line in
the Sierra Nevada.
Physical
weathering
dominates
Chemical weathering: decays rock by chemical reactions
decomposition
Operates in three ways by creating
1. new materials less resistant to erosion
2. new materials with greater volume  expansion
3. soluble materials which are easily dissolved
and transported in water
Most chemical weathering requires water
heat speeds up reaction
Chemical weathering is fastest in warm wet climates
Examples of Chemical
Weathering
Wet
Hot
Dry
Cold
1. Oxidation
chemical union with oxygen
usually creates softer and
finer material
increase in volume
(expansion)
Soil profile showing depth of chemical
weathering ‘front”
3
Examples of Chemical Weathering
2. Hydration...water attached without chemical change
 expansion, solution
Examples of Chemical Weathering
3. Hydrolysis...water unites chemically  new compounds
 expansion,  soluble compounds
4. Carbonation...formation of soluble carbonates
Examples of Chemical Weathering
5. Solution...dissolves minerals
Evidence of chemical weathering
Edges and corners along joints and bedding planes are
weathered more rapidly than flat surfaces  rounded edges
water soluble...NaCl, CaSO4 (gypsum)
acid soluble
carbonic acid, acid rain
can dissolve limestone
and marble (CaCO3)
Spheroidal weathering...in place
Elephant Rocks State Park, Missouri,
4
Chemically weathered niche, New Mexico
Chemical
weathering 
niche where
water seeps
out
Biological weathering
living organisms break down rock
physically and/or chemically
Physical examples
plant roots
burrowing animals
Chemical weathering dominates in warm & wet climates
 rounded shapes
Physical weathering dominates in drier cooler climates
 angular, jagged shapes
Chemical examples
lichen
acid litter
Differential weathering
Examples of differential weathering in different climates
one material breaks
down faster than
another
In warm wet climates
granite...subject to chemical weathering 
saprolite (rotten rock)
therefore, one is slower
to erode than the other
In cool dry climates, granite is resistant
mountains
5
In warm wet climates limestone dissolves
to yield topographic lows
At mineral level...silica (quartz) highly resistant to weathering
Released from rock by decomposition of surrounding
material, carried by streams to oceans  beaches
Appalachian Ridge and Valley...limestone valleys
and sandstone ridges
In cool or arid climates, limestone is resistant
often forms topographic highs
Gulf Shores sand comes mainly from Appalachians via the
Apalachicola River, deposited in offshore sand sheet.
GRAVITY AS AN AGENT OF GRADATION
Gravity causes mass movement (mass wasting)
Mass as in "matter" NOT as in large volume
Mass movement = movement of material downslope
under the influence of gravity
Factors influencing mass movement
1. Water
acts as a lubricant
adds weight
may cause “fluid” flow
2. Shaking as in earthquakes, explosions, trains
3. Undercutting by streams or human activity
4. Freeze/thaw or wet/dry cycles
Kind of
material
Rock
(dry)
Regolith
& water
Water &
sediment
Kind of
motion
Falling,rolling,
sliding
Flowage
within mass
Fluid
flow
Low
Slow
|
|
Talus
creep
Water
Content
High
Soil creep
|
|
Speed
|
|
|
|
Fast
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Slow
Slow
1. Creep...
1. Creep... Related to freeze/thaw or wet/dry cycles
Creep: gradual displacement downhill, greatest at surface,
most material moves by creep
Kind of
material
Rock
(dry)
Regolith
& water
Water &
sediment
Evidence of creep
Kind of
motion
Falling,rolling,
sliding
Flowage
within mass
Fluid
flow
Low
Slow
|
|
Talus
creep
Water
Content
High
Soil creep
Solifluction
|
|
Speed
|
|
|
|
Fast
2. Solifluction... water saturated soil, high latitudes or
elevations, permafrost beneath surface
Kind of
material
Rock
(dry)
Regolith
& water
Water &
sediment
Kind of
motion
Falling,rolling,
sliding
Flowage
within mass
Fluid
flow
Low
Slow
|
|
Talus
creep
Water
Content
High
Soil creep
Solifluction
|
|
Speed
Land-slides
Earthflows
slumps
|
|
|
|
Fast
7
1994, landslide, McClure Pass, CO
Landslide...mass of material moves as a unit
moves regolith (all material above bedrock)
sudden, moderately high speed
Earthflow...usually water soaked mass
clay rich soil on a slope
linear = earthflow
rotational = slump
All of above related to over-steepened slopes
stream (or construction) undercutting
earthquakes
loss of vegetation
water that adds weight / lubricates
http://www.ngdc.noaa.gov/seg/hazard/slideset/landslides
Earth flow: material mixes
Landslide: slippage on
straight plane
Earth slump: slippage
on a curved plane
La Conchita, CA,
1995
8
Landslide
http://www.youtube.com/watch?v=qEbYpts0Onw&fe
ature=related
Slump has a rotational element, slide does not
Kind of
material
Rock
(dry)
Regolith
& water
Water &
sediment
Kind of
motion
Falling,rolling,
sliding
Flowage
within mass
Fluid
flow
Low
Slow
|
|
Talus
creep
Water
Content
Rockfall: dry material
“falls” downhill,
common in spring thaw
High
Soil creep
Solifluction
|
|
Speed
Land-slides
Earthflows
slumps
|
|
|
Fast
Rockfall
Avalanche
Avalanche on Mt. Denali, Alaska
Kind of
material
Rock
(dry)
Regolith
& water
Water &
sediment
Kind of
motion
Falling,rolling,
sliding
Flowage
within mass
Fluid
flow
Low
Slow
|
|
Talus
creep
Water
Content
High
Soil creep
Solifluction
|
|
Speed
Land-slides
Earthflows
slumps
|
|
|
|
Fast
Rockfall
Avalanche
Debris
flow
Stream flow
|
9
Debris flow...water, mud, and rock debris
more fluid than earthflow
moves faster and follows valleys (channelized flow)
associated with
heavy rain
steep poorly vegetated slopes
arid and semi-arid regions
common in California
Csa (Mediterranean) climates
dry summers
fire destroys vegetation
wet winters
1980, San Bernadino, debris flood control basin overflowed
Debris flow
http://www.youtube.com/watch?v=X4JPxw578UE&fe
ature=related
Speed and water content are the main classification
variables for mass movement
Low
Slow
|
|
Talus
creep
Water
Content
High
Soil creep
Solifluction
|
|
Speed
Land-slides
Earthflows
slumps
|
|
|
|
Fast
Rockfall
Avalanche
Debris
flow
Stream flow
Moral of the story:
BE CAREFUL WHERE YOU BUY YOUR HOUSE
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