Weathering, Soil, and Mass Movements Chapter 5

Mechanical Weathering physical forces break rock into smaller and smaller pieces

Mechanical Weathering Frost wedging ◦ The mechanical breakup of rock ◦ talus Unloading ◦ exfoliation Biological activity

Chemical Weathering  transformation of rock into one or more new compounds  water is the most important agent of chemical weathering  Granite  made of quartz and feldspar  carbonic acid makes the feldspar become clay but the quartz stays the same  Weathering of Silicate Minerals  Produces insoluble iron oxides and clay minerals  Spheroidal Weathering  Causes the corners and edges of rock to be more rounded

Factors Affecting the Rate of Weathering Rock characteristics ◦ Mineral composition ◦ solubility ◦ Physical features Climate ◦ Temperature and moisture

Soil Composition Regolith ◦ layer that covers most of Earth’s land surface. mineral matter humus water air

Soil Texture and Structure Sand Silt Clay Loam

Soil Formation Parent material ◦Residual soil  Bedrock ◦Transported soil  Unconsolidated deposits Time Climate Organisms Slope

Soil Profile A horizon ◦ Topsoil B horizon ◦ subsoil ◦ contains clay particles from the A horizon C horizon ◦ between B horizon and parent material

Soil Types Pedalfer ◦ iron oxides and aluminum-rich clays in the B horizon ◦ Temperate regions with more than 63 cm of rain annually Pedocal ◦ calcium carbonate and less clay ◦ Usually in drier climates than pedalfer Laterite ◦Tropical climates so lots of water ◦Deeper soils ◦Red or orange color

Soil Erosion Water erosion ◦Sheet erosion ◦Rills, trenches, and gullies Sediment deposition ◦Too much sediment means a river has to be dredged and dams last less time ◦Pesticide and fertilizer contamination Controlling erosion ◦ Windbreaks ◦ Terracing hillsides ◦ Contour tilling ◦ Rotating crops

Mass movements Triggers ◦ Saturation with water ◦ Steep slopes ◦ Removal of vegetation ◦ Earthquakes Rockfall Slide ◦Rockslides Slump Flows ◦Mudflows ◦Earthflows Creep