Mechanical & Chemical Weathering Pages 40-45

Mechanical Weathering Joint—crack in a rock Joint—crack in a rock –1. Formed because rock is  Compressed  Pulled apart  Raised by tectonic forces –2. Widens as pressure is released

Types of Mechanical Weathering Frost Action—freezing of water in a joint, the water/ice expands widening the joint. The ice melts and water seeps deeper and the process repeats Frost Action—freezing of water in a joint, the water/ice expands widening the joint. The ice melts and water seeps deeper and the process repeats Exfoliation—peeling off of large curved sheets of rock from an exposed surface Exfoliation—peeling off of large curved sheets of rock from an exposed surface –Usually need a release of pressure –Temperature changes can speed this process

Exfoliation Forest fire in Glacier National Park (taken 8/2008)

Plant Action—growing roots weaken the rocks. Water pressure in the roots cracks rocks Plant Action—growing roots weaken the rocks. Water pressure in the roots cracks rocks Animal Activity—holes and burrows dug by animals lets air and water into the ground Animal Activity—holes and burrows dug by animals lets air and water into the ground Abrasion—”sand blasting” of rock by wind or water. Abrasion—”sand blasting” of rock by wind or water.

Chemical Weathering By Water By Water –Leaching—dissolves minerals and wash them away –Hydration—water combines with minerals— the minerals swell and become soft or brittle By Oxygen By Oxygen –Oxidation– minerals combine with oxygen in the air or water and forms oxides  Ex: Statue of Liberty=copper oxide  Rusting=iron + oxygen = iron oxide

Chemical Weathering By Acids By Acids –1. Carbon dioxide + water = carbonic acid  Carbonic acid dissolves calcite which is the glue for limestone –2. Decay of plants and animals produces acids –3. Acid rain produced by the burning of fossil fuels weathers rocks

Factors that affect Rates of Weathering Number and size of joints— – –increased surface areas  weather faster 2. Climate –Warm and moist climates  weather faster 3. Mineral Content 3. Mineral Content –Softer minerals  weather faster