Weathering Chapter 5

Weathering The breakdown and changing of Earth’s rocks through direct contact with the planet’s hydrosphere, biosphere, and atmosphere There are two types of weathering: mechanical and chemical

Mechanical Weathering or Physical Weathering occurs when rocks are cracked or broken into smaller pieces, without changing the rock’s composition 3 types of mechanical weathering are: Frost wedging Unloading Biological activity

Frost Wedging The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices Sections of rock that are wedged loose may tumble into large piles called talus, which typically form at the base of steep, rocky cliffs

Unloading Pressure released on igneous rock causes it to expand and allows slabs of outer rock to break off in layers in a process called exfoliation

Unloading (exfoliation)

Biologic Activity The activity of organisms, including plants, burrowing animals, and humans, can also cause mechanical weathering

Biologic Activity

Chemical Weathering The transformation of rock into a different substance or new compounds Types of chemical weathering are: Water Oxygen Carbon Dioxide Spheroidal

Water is the most important agent of chemical weathering Chemical reaction of oxygen with water (oxidation) Forms rust Chemical reaction of carbon dioxide with water (carbonic acid)

Water absorbs with sulfur oxides and nitrogen oxides, that are produced from burning fossil fuels, causes acid rain Spheroidal weathering changes the chemical composition and causes the corners and edges to be more rounded

Rate of Weathering Mechanical weathering affects the rate of chemical weathering Physical characteristics (mineral composition) of rocks influence the rate of weathering Climate, especially temperature and moisture, influence the rate of weathering