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 blue-green 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

1

2

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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 hasexperienced devastating

landslides in recent years

Slump

Slide

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