Rock Relationships
magma -> granite -> gneiss
sand -> sandstone -> quartzite
clay -> shale -> slate
peat -> bituminous coal -> anthracite coal
lime -> limestone -> marble
Weathering and Erosion
Weathering is the natural breakdown of solid rock into smaller fragments through chemical, physical, and biological processes.
Physical weathering includes frost wedging and bedrock expansion.
Chemical weathering includes oxidation and acid-base reactions between rock and rain water. Oxidation is the combining of oxygen with elements in the rock such as iron and copper. Oxidation causes iron to turn red and copper to turn green.
Biological weathering is caused by living things. Plant roots wedge rocks apart in a process called root pry. Animals can burrow into rock crevices. Chemicals produced by lichens can slowly eat away at rocks.
Erosion is the loosening, wearing away, and transport of soil and rock fragments by gravity, running water, ice, or wind.
Mass movement is the downhill movement of rock or soil caused by gravity. Examples include rockfalls, creep, and mudflows. Rockfalls can cause the accumulation of talus, large angular rocks, at the base of cliff or steep slope.
Running water is the most common cause of erosion. The running water picks up soil and rock particles that rub against rocks slowly wearing them away in a process called abrasion. Like a nail file against a fingernail, the particles wear away the rock.
The wind lifts particles and blows them away from surfaces in a process called deflation.
Glaciers are large sheets of ice that creep downhill. The massive weight of the glacier pushes through valleys scouring rock surfaces and breaking of peices of rock. The rocks and soil trapped in the glacier grind against other surfaces as the glacier moves. The edge of the glacier leaves a terminal moraine of rocks. It deposits them like a bulldozer.
