Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Weathering The break down of rocks on the Earth’s surface. Two Types The two types of weathering are: 1. Mechanical weathering – rocks are physically broken into smaller pieces, but there is no chemical change in the rock. 2. Chemical weathering – the chemical composition of rocks is altered. Types of Mechanical Weathering 1. Frost Wedging – occurs when water is trapped inside the cracks of a rock and then freezes. The ice expands and exerts a force strong enough to fracture the rock. 2. Crystal Growth – occurs when saltwater enters a crack in a rock and then evaporates. It leaves behind salt crystals which can exert force and enlarge the cracks. Types of Mechanical Weathering 3. Thermal Expansion – occurs when rocks are exposed to severe heat. The crystal structure of the minerals in the rock expand, causing the outer layers of the rock to peel off. 4. Root Penetration – occurs when plants and trees take root in the crevices of rocks. The growing root can expand the crevice. Root Penetration Types of Mechanical Weathering 5. Mechanical Exfoliation – occurs after an intrusive igneous rock has been exposed at the surface by erosion of overlying rock. The overlying rock no longer exerts pressure on the igneous rock and so it expands outward, fracturing into sheets parallel to its exposed surface. 6. Abrasion – occurs when rocks and particles collide and grind each other. Mechanical Exfoliation Types of Chemical Weathering 1. Dissolution – water removes chemicals (ions) from a rock and carries them away. Halite (rock salt) dissolves like table salt. Limestone is dissolved when water (H2O) and carbon dioxide (CO2) in the atmosphere combine to form carbonic acid (H2CO3). Sulfuric acid (H2SO4) may also be formed and it dissolves limestone quite rapidly. Dissolution of Limestone Types of Chemical Weathering 2. Oxidation – this is another word for rust. The surfaces of iron-rich rocks will rust when they come in contact with water. Copper develops a green surface. Oxidation Oxidation Types of Chemical Weathering 3. Hydrolysis – occurs when water ions displace another element in the mineral’s structure, forming a different mineral. Aluminum-rich rocks are weathered by hydrolysis forming clays. Factors That Affect Weathering Climate – warm, moist climates (tropics) have the highest rates of chemical weathering. Living Organisms – burrowing animals (earthworms, groundhogs, ants) transport unweathered rocks from below ground to the surface where they can be exposed to weathering agents. Factors That Affect Weathering Time – the longer a rock is exposed to weathering agents, the more it will decompose. Mineral composition – rocks composed of silica strongly resist weathering, while those containing iron, halite, and limestone are more susceptible to weathering.