Chemical Weathering PDF

# Chemical Weathering Unlike mechanical weathering, which changes only the size and shape of a rock, chemical weathering changes the rock into a different substance. ## Types of Chemical Weathering - **Oxidation** - Rust - Oxygen + Iron = Iron Oxide (rust) - Most metal products we us...

# Chemical Weathering Unlike mechanical weathering, which changes only the size and shape of a rock, chemical weathering changes the rock into a different substance. ## Types of Chemical Weathering - **Oxidation** - Rust - Oxygen + Iron = Iron Oxide (rust) - Most metal products we use have protective coating to slow down oxidation, but rocks have no protection, so rust can gradually eat away the metal contained in some rocks. - **Reaction of Acids** - Occurs when water carries chemicals from the air onto surfaces below. - Water + Carbon Dioxide = Carbonic acid. - Though carbonic acid is relatively weak over long periods of time rain containing the acid can dissolve certain kinds of rock. - Carbonic acid itself is not harmful to plant life. - However, man has introduced additional chemicals to the atmosphere by burning fossil fuels such as oil and coal making a stronger acid solution called acid rain. - Industrial cities are more likely to have this kind of chemical weathering. ## Lichens and Mosses - Lichens and mosses can survive on the little water and soil they find on some rocks. - While attached to the rocks, these organisms secrete mild acids that dissolve the rocks and further break down the rocks into soil ## Caves - Weathering forms many kinds of caves. - **Chemical Weathering Forms** - Limestone caves, or caverns. - **Stalactites** - Cave formations that hang from the ceiling and look like stone icicles. - **Stalagmites** - Cave formations that "grow" up from the ground as a result of dripping calcite. - **Drip Curtain** - Stalactites - coiling - Stalagmites - ground - **Columns** - A cave formation from water seeping in along a crack and hardening, leaving a long, delicate, curtain-like sheet. - **Columns** - Forms when a stalactite and a stalagmite grow together. - **Spelunkers** - People who enjoy exploring caves are called spelunkers # What is Weathering? - Deep within the earth, heat and pressure form and transform rocks, while on the surface, wind and water break down and move rocks. - These natural processes are continually changing the surface of God's Earth. ## Rock Cycle - Three rock categories - Igneous - Sedimentary - Metamorphic - Scientists call the changing of rock the rock cycle. - Most kinds of rocks are very hard, but even the hardest rocks can be broken down into gravel and pebbles, sand, silt, or powdery clay. ## Weathering - The process of breaking down rocks - Two main types of weathering - Mechanical weathering (or Physical weathering) - Chemical weathering - **Mechanical Weathering** - Breaks rocks into smaller and smaller pieces. - **Chemical Weathering** - Transforms rocks into new substances. - Both kinds of weathering take place at or near the Earth's surface and are greatly affected by temperature and moisture. - The process of weathering usually takes years or even centuries, but slowly, little by little, big rocks are worn away into smaller pieces. # Mechanical Weathering - **Mechanical (or Physical) Weathering** - The process of breaking down rocks into smaller pieces. - **Things that affect weathering**: - Water - Wind - Temperature - Pressure - Plant and animal life - **Types of mechanical weathering**: - **Frost Wedging or Frost Action**: - Water gets into the cracks of a rock, freezes, expands, and makes the cracks bigger. - **Frost Heaving**: - Water gets underneath a rock and pushes the rock up out of the ground. - **Pressure Release**: - Shifts in the ground reduce the pressure on a rock causing it to expand, suddenly creating cracks in the rock. - **Exfoliation**: - Sheets of rock peal away like layers of an onion - **Abrasion**: - Rocks rub against each other gradually wearing one another away - **Abrasion**: - Can be caused by water or wind. - **Plants and Animals Contribute to Weathering**: - When soft rocks wear away faster than hard rocks creating unusual rock formations. - Some rocks expand to break in the middle. - Just as ice expands to break rocks, the roots of a sprouting seed may grow in the middle of a rock causing it to break apart as the plant grows. - **Fires, floods and other catastrophic events can also cause Mechanical Weathering**