WEATHERING EROSION WEATHERING and the BREAKDOWN of ROCKS The process by which rocks and minerals break down at or near the surface of the Earth. The process by which moving water, wind, ice or gravity carries away pieces of rock and deposits it elsewhere. WEATHERING and EROSION are inter-related. WEATHERING speeds EROSION.

WEATHERING PROCESSES MECHANICAL WEATHERING WEATHERING and the BREAKDOWN of ROCKS MECHANICAL WEATHERING breaks a mineral or rock into smaller pieces but does not change the chemical make-up of the pieces. Turns big rocks into little rocks. Mechanical Weathering increases the surface area that can later be chemically weathered.

FROST WEDGING WEATHERING and the BREAKDOWN of ROCKS Water expands when frozen. Expands ~ 9%. Water trapped in cracks freezes and expands. Actively fractures the rock. Works best where temperatures fluctuate above and below 0  C (32  F). When water melts, it seeps deeper into the crack and then refreezes.

FROST WEDGING WEATHERING and the BREAKDOWN of ROCKS Breaks off blocks or slabs of rock. Broken pieces fall downslope. Accumulate as TALUS.

FROST WEDGING FROST HEAVES AND POTHOLES WEATHERING and the BREAKDOWN of ROCKS

CRYSTAL GROWTH Salt water, usually from the ocean, gets into fractures. When it evaporates, crystals grow that expand. Expansion of crystals breaks the rock. Before After Cleopatra’s Needle Central Park, NY WEATHERING and the BREAKDOWN of ROCKS

THERMAL EXPANSION and CONTRACTION Heat causes external layers of rock to expand. Mineral expand at different rates. Quartz expands more than feldspar. Those minerals that expand more, exert pressure on those that expand less. Generally affects only the surface layer of a rock. (Rock is a poor conductor of heat) Forest Fire High alternation of temperatures (deserts) Water or moisture speeds the process. WEATHERING and the BREAKDOWN of ROCKS

MECHANICAL EXFOLIATION When overlying mass of rock and sediment is released, pressure on the underlying rock is released. Allows the rock to expand. Expansion takes place outward from the exposed surface. Sheets of rock will fall off. WEATHERING and the BREAKDOWN of ROCKS

MECHANICAL EXFOLIATION WEATHERING and the BREAKDOWN of ROCKS

MECHANICAL WEATHERING OTHER TYPES ROOT WEDGING Trees grow in cracks in rocks and the force related to expansion with growth breaks the rocks. WEATHERING and the BREAKDOWN of ROCKS

MECHANICAL WEATHERING OTHER TYPES ABRASION Contact of weathered and eroded particles with other rock during erosion also leads to mechanical breakage due to ABRASION. WEATHERING and the BREAKDOWN of ROCKS

CHEMICAL WEATHERING Causes a change in the chemical composition of rocks and minerals being affected. Attacks rocks and minerals that are unstable at the Earth’s surface first. Produces stable byproducts. Minerals that are stable at the Earth’s surface are less affected by chemical weathering. Most change takes place through contact with water. Watercarries ions from place to place participates in the reaction itself carries away the products = erosion. WEATHERING and the BREAKDOWN of ROCKS

CHEMICAL WEATHERING Chemical weathering occurs faster when weathered material is broken up first by mechanical weathering. Increased surface area allows chemical weathering to occur at a faster rate. WEATHERING and the BREAKDOWN of ROCKS

CHEMICAL WEATHERING DISSOLUTION Water removes ions or ion groups from a rock or mineral and carries them away. Precipitate later when water evaporates. Due to the bipolar nature of water molecules, ions become dissolved and are transported in solution. WEATHERING and the BREAKDOWN of ROCKS