Weathering / Soils

http://youtu.be/Xdg1lpQfLbo

Weathering The process by which natural forces break

down rocks Erosion: The break up and transport of earth

materials

Mechanical Weathering The breaking up of rocks by physical forces Ice Wedging: water freezing, expanding and

splitting rock Pressure release: (exfoliation) Inside pressure

causes rock to expand when overlying burdens are removed

Plant root growth: plant roots expand cracks Abrasion: wearing down by friction (moving water

rubbing rocks against each other)

Ice Wedging

Root growth

Exfoliation Abrasion

Chemical Weathering Breakdown of rock by chemical reactions Dissolving: minerals dissolving in water or

weak acids Rusting: Iron in rocks combining with

oxygen to produce rust (iron oxide)

Soil A mixture of weathered rock particles,

organic matter, water and air Humus: decayed plant and animal material

Soil Horizons A horizon: upper most layer (topsoil)

containing the most humus. Darkest layer B horizon: little humus, brown to reddish

brown, contains clay that washes down from A horizon

C horizon: deepest layer, largest least-weathered rock particles, light yellowish brown

Soil Properties Texture: size of particles in soil Sand: largest, visible, feels gritty Silt: smaller – microscopic, feels silky Clay: smallest – microscopic, feels sticky

when wet

Properties continuedColor: comes from iron compounds and humushumus – black, iron – reddishoriginal rock- yellows or tansbright colored soils drain wellPore space: the spaces between particlesChemistry: pH (acidity) determines how well

nutrients dissolve