Unit # 3: Gradational
Processes
Ms. Bader
Weathering, Erosion,
Transport, Deposition and
Mass Wasting
Processes of …
• Denudational/Gradational process = The
processes that wear down the Earth's
surface features through weathering, mass
wasting, erosion, and deposition.
• Aggradation = building up the land
surface!
• Originates in the atmosphere and
hydrosphere.
• Gradation includes three different and
complimentary processes; Weathering,
Transport and Deposition.
Weathering
• The process of rocks or other substances
breaking down at or near the Earth’s
surface.
• Three Types (Mechanical, Chemical and
Biological)
• The products of weathering are a major
source of sediments for erosion and
deposition.
Types of Weathering
• Chemical Weathering
• Mechanical Weathering
• Biological Weathering
Mechanical Weathering
Mechanical weathering
is the physical break
down of a material
without altering its
chemical composition.
Common in desert and
arctic environments
where the lack of
vegetation exposes the
surface
Agents of Mechanical
Weathering
Abrasion (grinding by friction)
Exfoliation/Sheeting (layers peel off)
Frost Action (ice expands)
Organic Activity (tree roots)
Gravity
Textbook Terms
• Frost Shattering – when water enters a
crack in the rocks, freezes and expands.
• Thermal Expansion – when rocks
(especially in deserts) expand rapidly
when the sun hits them after a cold night.
• Differential weathering – occurs when
softer minerals of rocks erode away
leaving the more resistant minerals in
place
Textbook Terms
• Exfoliation – where layers of an igneous rock
“peel” off as the pressure that keeps them intact
is lost (from the crust) when the rock moves to
the surface.
Interesting Fact!
• In the arctic tundra, a pingo begins when
pools of standing water in low areas
gradually expand to become a thaw lake.
Chemical Weathering
Chemical Weathering
is the alteration of the
chemical composition
of a material in
breaking it down.
Prevalent in warm and
wet climates, where
moisture can carry
chemicals into the
rocks.
Agents of Chemical Weathering
Carbonation
Oxidation
Acid Rain
Plant Acid
Hydrolysis
Chemical Reactions
• Carbonation = Carbonation occurs when carbon
dioxide is dissolved in water and eats away at
rocks.
• Oxidation = many rocks contain iron which
exposed to air oxidizes (rust-red colour or bluegreen for copper).
• Acid Rain = reacts with certain rocks, such as
limestone. This causes them to wear away more
quickly.
• Hydrolysis = when carbonic acid reacts with
silicon in rocks, such as sandstone and replaces
ions of silicates with ions of water, hence rock
breaks.
Karst
• The chemical weathering of carbonate-rich rocks
creates a unique landscape abounding in caves,
disappearing streams, and springs.
• Karst, a Yugoslavian term that comes from a
narrow strip of limestone plateau noted for the
assemblage of solution landforms.
• Karst develops in regions underlain by limestone
and to a lesser extent dolomite. Chemical
solution of the limestone, especially when
fractured, wears away the bedrock leaving
fissures and possibly undermining the surface.
Stalactites hang from the ceiling and stalagmites grow
from the floor of Carlsbad Caverns, NM
Biological Weathering
• Involves the disintegration of rock and mineral
due to the chemical and/or physical agents of an
organism. The types of organisms that can
cause weathering range from bacteria to plants
to animals.
• Simple breaking of particles, by the consumption
of soils particles by animals. Particles can also
fracture because of animal burrowing or by the
pressure put forth by growing roots.
• And simple respiration processes (CO2
production can lead to a chemical reaction!).
Rates of Weathering
4
3
2
1
1. Tropical rainforest
2. Hot desert
3. Temperate mountains
4. Polar Regions
Rates of Weathering
Ontario, Canada
Annual
Temperature: 8.9
Celcius
Annual Rainfall:
891 mm
Rates of Weathering
Under average condition, rates of weathering
is an extremely slow process. The key three
factors are:
1.Surface Exposure
2.Composition of Rock – Resistant and
texture
3.Climatic Conditions
Transport and deposition
• Transport refers to the movement of weathered
material from one place to another.
• The more energy there is, the more materials
can be carried.
• Load = refers to material being carried and
when it comes to a rest we say it has been
deposited.
• Speed of an agent of deposition indicates what
type of deposition can be created such as,
Sandbars, Scree Slopes (masses of coarse
rocks from avalanches), moraines etc.)
Mass Wasting
• Mass movement is the down slope
movement of earth materials under the
influence of gravity.
• The detachment and movement of earth
materials occurs if the stress imposed is
greater than the strength of the material to
hold it in place.
Mass Wasting
• The energy that is exerted by gravity on a
load is determined by the following factors:
– Steepness of Slope
– Shape and size of particles
– Nature of materials that form the slope
– Depth of the weathered materials
– Nature of ground cover
– Stability of ground
– Water content in the soil
Types of Mass Movement
• Soil creep is nearly imperceptible to the naked
eye as it is the slowest of all types of mass
movement. (Moves millimeters to under a meter
per year!)
• Soil creep generally occurs in the top few meters
of the surface and is accomplished by expansion
and contraction of the soil.
– For instance, when water in the soil freezes the ice
pushes soil particles outward perpendicular to the
slope. Upon warming, the ice melts and the soil is
pulled down slope under the influence of gravity. Over
many freeze-thaw cycles soil moves slowly down
slope.
Soil Creep
Slides and Slumps
• A slide is a sheet of material that slips over a
failure plane ending anywhere from a meter to a
kilometer down slope.
• A slump is a landslide where the underlying
rock masses tilt back as they slide from a cliff or
escarpment. Slumps are sometimes caused by
clear cutting on unstable soils.
• Slumps produce concave scars while slides
tend to produce a scarp or cliff exposure. Trees
are broken and bent and the slide can bury the
soil down slope.
La Conchita, California has
experienced devastating
landslides in recent years
Slide
Slump
Solifluction
• Solifluction is the down slope movement
of soil over a permanently frozen
subsurface.
• Solifluction is common on slopes
underlain by permafrost. During the
summer when the upper permafrost is
activated, the waterlogged soil mass
slowly moves down slope to form
solifluction lobes or terraces.
Solifluction
Mudflow
• A mudflow is the rapid down slope movement
of water-saturated water- saturated soil. The
higher water content creates a flow rapid
enough to be perceptible to the eye.
• Conditions favorable for the development of
mudflows are: (1) unconsolidated surface
materials, (2) steep slopes abundant but
intermittent precipitation, and (3) sparse cover of
vegetation.
• Mudflows tend to be more prevalent in dry
regions where vegetation is sparse and heavy
rains may form.
Mudflow
Rock Flow
• Rock fall is one of the most sudden forms
of mass movement. Rock fall occurs when
blocks of rock shed from a cliff face and
collect at the base. This is the quickest
form of mass movement!
• Talus is a term that is applied to an
accumulation of rock by rock fall.
Rock Flow