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WEATHERING. Weathering is the breaking down of earth rocks and matter. Weathering is. Breaking of rocks into smaller particles by mechanical and chemical processes.
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WEATHERING Weathering is the breaking down of earth rocks and matter.
Weathering is • Breaking of rocks into smaller particles by mechanical and chemical processes. • Not the same thing as erosion. The two processes of weathering (wxing) and erosion work together. We will look at erosion in more detail later, but for now will define erosion as the movement of weathered materials.
Mechanical Weathering • Sometimes called Physical Weathering, also known as Disintegration. • Breaks rocks into pieces which become sediments. • Some types include frost wedging, root pry, exfoliation, and abrasion by wind blown sand, water borne sediments, and glacial gouging. .
Types of Mechanical Weathering • Exfoliation is caused by the expansion and contraction of surface rocks exposed to sunlight during the day and cool nights. • Exfoliation causes the surface of rocks to peel off in sheets.
Mech Wxing, continued • Frost Wedging occurs when liquid water collects in small openings in rocks, freezes and expands to push them apart a bit. • The enlarged opening allows more water to collect for the next cycle. • Frost Wedging is most effective in temperate (moderate) climates.
Melted Snow runs into crack to enlarge what could become a pothole.
Lichen and Frost Wedging Attacking a Rock’s Surface, Christiansburg VA
Mech Wxing: Frost Wedging • Root Pry is a slow, but powerful process where plant roots grow into cracks in rocks and enlarge them.
Impressive Root Pry, Huckleberry Trail, Montgomery County VA
Mech Wxing: Abrasion • Abrasion is caused by wind blowing particles onto exposed rocks. It is similar to the process of sand blasting. • Running water and waves have a similar effect. Particles scour away rocks. • Glaciers carry rocks which stick out the edges and rasp away grooves called striae.
No Glaciers in VA, but you can see that ice will move and flow – Rock Road, Radford
Chemical Weathering • Chemical Weathering is also called Decomposition. • The products of chemical wxing are ions, electrically charges particles. • Chemical wxing requires liquid water. It is also more powerful in warmer temperatures. So chemical weathering is most effective in tropical climates.
Agents of Chemical Wxing • Rain is naturally acidic, but not very strong. Carbon dioxide (CO2) dissolves in raindrops to form carbonic acid, HCO3 • Sulfur Dioxide (SO2)from coal power plants and volcanoes dissolves into water to make sulfuric acid, H2SO4. • Decaying plant matter (humus) makes Humic acid. • Oxidation is chemical change that occurs when O2 reacts with rocks; water helps this.
This building has been exposed to acid rain from coal fires for centuries. The Tower of London.
Less than 100 years old, Memorial to Wright Brothers’ Flight, Kitty Hawk, NC
Chemical Wxing, cont’d. • Acids react with rocks to separate atoms and ions which dissolve in water and are carried away. • Carbonate rocks, such as our local limestones, are particularly affected by acids, which is why we have caves. Tougher rocks stick out of the ground, giving us our karst terrain (caverns, sinkholes, disappearing streams.)
A cavern collapsed and this sinkhole developed in Orlando FA. It swallowed a house and an exotic car dealership. No lives lost.
The Importance of Weathering • Weathering is an important part of the rock cycle. • Weathering helps build new soil, so fresh nutrients are available for plant growth. Plants are the main base of our food web.
