CH 12 Weathering, Soil, Mass Movements (Gravity) Earth’s surface is constantly changing. Earth’s surface is constantly changing. Weathering = breaking down and changing of rocks at or near earth’s surface. Weathering = breaking down and changing of rocks at or near earth’s surface. 2 types of weathering 2 types of weathering Mechanical and chemical Mechanical and chemical

Mechanical Weathering The break up of rocks by physical forces without changing their mineral composition The break up of rocks by physical forces without changing their mineral composition 1 – Frost wedging – water seeps into cracks, freezes, expands, and enlarges them (talus) 2 – Unloading – reduced pressure causes outer layers to flake off (exfoliation) 3 – Biological activity – root wedging and burrowing of animals

Chemical Weathering The transformation of rock into one or more new compounds The transformation of rock into one or more new compounds Water is the most important chemical agent Water is the most important chemical agent 1 – Oxidation = rusting 2 – Hydrolysis = rock reacts with water. 3 – Carbonation = water and carbon dioxide (CO 2 ) form carbonic acid (a weak acid) that reacts with limestone and marble. Granite weathers to clay. * Spheroidal weathering – read pages 130/131

Rates of Weathering 4 Factors 4 Factors  (1) Rock characteristics – cracks, mineral content, hardness  (2) Climate – humid vs dry, very cold vs moderate, acid rain  (3) Differential weathering – cap rock  (4) Surface area –

Soil Produced by weathering Produced by weathering 3 soil characteristics 3 soil characteristics  A) composition: 1-sediments, 2-organic matter (humus), 3-water, 4-air  B) Texture: refers to the portion of different particle sizes (pg 227)  C) Structure: determines how easily it can be cultivated, eroded, or penetrated by water.

Soil Formation Factors Parent material: residual vs transported Parent material: residual vs transported Time: takes time… Time: takes time… Climate: greatest effect on soil formation Climate: greatest effect on soil formation Organisms: more organisms will produce better/more humus Organisms: more organisms will produce better/more humus Slope: steeper slopes have less/worse soil Slope: steeper slopes have less/worse soil

Soil Profile A cross sectional view of the soil A cross sectional view of the soil Each layer is called a horizon Each layer is called a horizon A-horizon = topsoil, dark/rich/humus (organic material) A-horizon = topsoil, dark/rich/humus (organic material) B-horizon = subsoil, leached minerals, lighter color, has clay B-horizon = subsoil, leached minerals, lighter color, has clay C-horizon = partially weathered bedrock C-horizon = partially weathered bedrock Bedrock = unweathered parent material at bottom Bedrock = unweathered parent material at bottom

Soil Types Read about it on page 139 Read about it on page 139

Soil erosion Rills – small channels Rills – small channels Gullies – large channels Gullies – large channels Sheet erosion – washing over entire surface Sheet erosion – washing over entire surface

Rates of Erosion Vegetation: less vegetation = more erosion Vegetation: less vegetation = more erosion Pavement: more pavement = more erosion Pavement: more pavement = more erosion Slope: steeper slope = more erosion Slope: steeper slope = more erosion Rain: longer and stronger = more erosion Rain: longer and stronger = more erosion Type of soil: more clay = more erosion Type of soil: more clay = more erosion Rock type: more shale = more erosion Rock type: more shale = more erosion

Mass Movement The transfer of rock and soil downslope due to gravity = mass movement The transfer of rock and soil downslope due to gravity = mass movement Some are fast, some are slow Some are fast, some are slow The factors that trigger it are water, oversteepened slopes, vegetation removal, earthquakes The factors that trigger it are water, oversteepened slopes, vegetation removal, earthquakes

Types of Mass Movement Falls – rocks fall quickly (talus) Falls – rocks fall quickly (talus) Flows – earthflow, mudflow (tongue or lobed shaped) Flows – earthflow, mudflow (tongue or lobed shaped) Slides – a block of material slides Slides – a block of material slides Creep – slow movement due to freezing and thawing (leaning stuff) Creep – slow movement due to freezing and thawing (leaning stuff) Slump – block of material moves in a curved shape (a scar is evident) Slump – block of material moves in a curved shape (a scar is evident)

Farming and Soil Conservation Crop rotation Crop rotation Wind breaks Wind breaks Terraces Terraces Contour plowing Contour plowing Ground cover Ground cover Strip cropping Strip cropping

Prevention of Mass Movement Retaining walls Retaining walls Vegetation Vegetation Bolts Bolts Fencing Fencing Stepping Stepping Diversion chutes Diversion chutes