Weathering: the physical breakdown (disintegration) and chemical alteration (decomposition) of minerals and rocks at of near the Earth’s surface Erosion: removal of weathered material (by water, wind, or ice)
3 Types of Weathering: 1. Physical/Mechanical Weathering: –Physical forces break rocks into smaller pieces without changing chemistry –4 kinds a)Frost action/ice wedging: water seeps into cracks, freezes, expands (9%) and pushes rock apart. Most effective in areas where temperature fluctuates above & below 0’C animation link
b) pressure release: many minerals/rocks are formed under immense pressure. When they are uplifted and exposed through erosion, the pressure is greatly reduced. The rock expands forming layer of fractures (joints) Sheet joints
Exfoliation: slabs of rock break along sheet joints and fall off Popping/rock bursts: sudden pressure relief in deep mines rock explodes like a grenade injuring/killing miners before after Exfoliation dome
c) Thermal expansion & contraction: rock is a poor heat conductor; in deserts where the temperatures rise and fall 30’C/day, the outside of the rock heats- expands and cools-contracts animation animation daynight + dark minerals get hotter than white minerals
2. Biological Weathering = activities of organisms a) animals: burrow, tramp, bring materials to surface for more weathering, help transmit gases and water to depths, etc. Animation Animation b) plants: roots wedge rocks apart Animation
3. Chemical Weathering: chemical alteration of rock/parent material 3 kinds a) Solution: a solid dissolves (halite, calcite) and is usually helped by CO 2 in water which forms carbonic acid (also in plant roots) Results in hard water, caves & karst topography (sink holes).
b) oxidation: reacts with oxygen to form oxides (rust). Ferromagnesians (olivine, pyroxene amphibole & biotite) combine with O 2 for form hematite or limonite. Hi sulfur/sulfide coal acid rain/runoff Iron sulfides (pyrite FeS 2 ) sulphuric acid + iron oxide