Mechanical & Mechanical & Chemical WeatheringChemical Weathering

Pages 40-45Pages 40-45

Mechanical WeatheringMechanical Weathering

Joint—crack in a rockJoint—crack in a rock– 1. Formed because rock is 1. Formed because rock is

CompressedCompressed Pulled apartPulled apart Raised by tectonic forcesRaised by tectonic forces

– 2. Widens as pressure is released2. Widens as pressure is released

Types of Mechanical Types of Mechanical WeatheringWeathering

FrostFrost ActionAction—freezing of water in a —freezing of water in a joint, the water/ice expands widening joint, the water/ice expands widening the joint. The ice melts and water the joint. The ice melts and water seeps deeper and the process repeatsseeps deeper and the process repeats

ExfoliationExfoliation—peeling off of large curved —peeling off of large curved sheets of rock from an exposed surfacesheets of rock from an exposed surface– Usually need a release of pressureUsually need a release of pressure– Temperature changes can speed this Temperature changes can speed this

processprocess

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

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

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

Plant ActionPlant Action—growing roots —growing roots weaken the rocks. Water pressure in weaken the rocks. Water pressure in the roots cracks rocksthe roots cracks rocks

Animal ActivityAnimal Activity—holes and burrows —holes and burrows dug by animals lets air and water dug by animals lets air and water into the groundinto the ground

AbrasionAbrasion—”sand blasting” of rock —”sand blasting” of rock by wind or water.by wind or water.

Chemical WeatheringChemical Weathering

ByBy Water Water – Leaching—Leaching—dissolves minerals and wash dissolves minerals and wash

them awaythem away– HydrationHydration—water combines with minerals—water combines with minerals

—the minerals swell and become soft or —the minerals swell and become soft or brittlebrittle

By OxygenBy Oxygen– OxidationOxidation– minerals combine with oxygen – minerals combine with oxygen

in the air or water and forms oxidesin the air or water and forms oxides Ex: Statue of Liberty=copper oxideEx: Statue of Liberty=copper oxide Rusting=iron + oxygen = iron oxideRusting=iron + oxygen = iron oxide

Chemical WeatheringChemical Weathering

By AcidsBy Acids– 1. Carbon dioxide + water = carbonic 1. Carbon dioxide + water = carbonic

acidacid Carbonic acid dissolves calcite which is the Carbonic acid dissolves calcite which is the

glue for limestoneglue for limestone

– 2. Decay of plants and animals 2. Decay of plants and animals produces acidsproduces acids

– 3. Acid rain produced by the burning of 3. Acid rain produced by the burning of fossil fuels weathers rocksfossil fuels weathers rocks

Factors that affectFactors that affectRates of WeatheringRates of Weathering

1. 1. Number and size of joints—– increased surface areas weather

faster 2. Climate

– Warm and moist climatesWarm and moist climates weather weather fasterfaster

3. 3. Mineral ContentMineral Content– Softer mineralsSofter minerals weather faster weather faster