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Aim: Weathering What are the different types of processes that break down rocks? • The breakdown of rocks and other materials on the Earth’s surface • It is a slow and continuous process that affects all substances exposed to the atmosphere Two types of weathering: 1. Physical • Occurs when rocks are broken down into smaller pieces called sediments • There is no change in composition Agents of Physical Weathering: • • • • Frost Action Abrasion Exfoliation Root Pry (Root Wedging) Frost Action When water repeatedly freezes and thaws in a small crack in a rock it will expand and force the rock apart Abrasion • The wearing down of rocks when they are rubbed against each other as they are carried by rivers and ice • Occurs mainly dry areas Here, the photo shows some pits that have been eroded into the rock by sandblasting The powerful effect of wind generated abrasion (Double Arch from Arches National Park) Exfoliation • The peeling away of large sheets of loosened material at the surface of a rock Root Pry • Roots from plants grow into cracks in rocks searching for nutrients and cause the rock to break apart 2. Chemical Weathering • Changes in the mineral composition or chemical makeup of a rock • Minerals can be added, removed or broken down Hydration • When water unites with certain minerals such as feldspar and they crumble into small particles of clay Oxidation • When oxygen combines with iron to form iron oxide (rust) Carbonation • Carbon dioxide dissolves in water to form carbonic acid • Dissolves large amounts of limestone Organic Decay • The decay of plants produces acids which dissolve minerals causing rocks to break down • Much like carbonation