Weathering

Weathering Process that breaks down and changes rock at or near earth’s surface Process that breaks down and changes rock at or near earth’s surface Mechanical – rock is broken into smaller pieces by physical means Mechanical – rock is broken into smaller pieces by physical means Chemical – rock undergoes changes due to a chemical change in composition Chemical – rock undergoes changes due to a chemical change in composition

Mechanical Weathering Two factors that are important to mechanical weathering are temperature and pressure. Two factors that are important to mechanical weathering are temperature and pressure.

Frost wedging

Exfoliation bedrock is under pressure within the earth; as it is exposed to the surface the pressure is reduced and the rock expands and long curved cracks form; layers of rock are stripped away bedrock is under pressure within the earth; as it is exposed to the surface the pressure is reduced and the rock expands and long curved cracks form; layers of rock are stripped away

Root action Root action

Abrasion

Chemical Weathering Chemical reactions take place that alter the rocks composition Chemical reactions take place that alter the rocks composition

Water: can dissolve many kinds of minerals and rock Water: can dissolve many kinds of minerals and rock Oxygen: can combine in chemical reactions with other substances – oxidation. Example: rust Oxygen: can combine in chemical reactions with other substances – oxidation. Example: rust Carbon dioxide combines with water in the atmosphere to create carbonic acid which dissolves rocks Carbon dioxide combines with water in the atmosphere to create carbonic acid which dissolves rocks Acid precipitation Acid precipitation

Factors affecting the rate of weathering Climate Climate Rock type and composition Rock type and composition Surface area Surface area topography topography

Erosion The transport of weathered material form one place to another The transport of weathered material form one place to another

Forces that aid erosion The force of gravity tends to pull materials downslope. The force of gravity tends to pull materials downslope

Running water Running water has greater erosional power than wind and can move more material greater distances. Running water has greater erosional power than wind and can move more material greater distances. As the slope of the As the slope of the land decreases, the water slows and larger particles are deposited.

Glacial erosion Due to their high density glaciers carry huge rocks and piles of debris and scratch and grind over surfaces. Due to their high density glaciers carry huge rocks and piles of debris and scratch and grind over surfaces. Erosion by abrasion Erosion by abrasion

Wind erosion Wind picks up and moves fine particles Wind picks up and moves fine particles Prevalent in areas of low precipitation and high temperatures Prevalent in areas of low precipitation and high temperatures

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Mass Movements The downslope movement of loose sediment and weathered rock due to gravity The downslope movement of loose sediment and weathered rock due to gravity Influenced by Influenced by weight of material weight of material materials resistance to sliding/flowing materials resistance to sliding/flowing a trigger a trigger water water

Types of mass movement Creep – slow, steady downhill movement Creep – slow, steady downhill movement Flows – materials flow as if thick liquid Flows – materials flow as if thick liquid Slides – rapid, downslope movement of a thin layer of material that separates from underlying bedrock Slides – rapid, downslope movement of a thin layer of material that separates from underlying bedrock Slumps – mass of material rotates and slides along a curved surface Slumps – mass of material rotates and slides along a curved surface Avalanches – landslides that occur in mountainous areas with thick accumulations of snow Avalanches – landslides that occur in mountainous areas with thick accumulations of snow Rock falls – rocks break loose and fall downward Rock falls – rocks break loose and fall downward

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