Soils "A critical sustaining structure for plants, animals, and human life." (Elemental Geosystems)
Soil: combination of sediments and decayed organic matter (humus) and empty pore space.
Weathering: disintegration and decomposition of rock at or near the surface.
Formation processes of water: Water percolating down - moves and removes soluble material, leaching.Evaporation makes water soak upwards causing minerals to precipitate
salinization - Over irrigation in dry regions causes the water table to rise allowing ground water to soak upwards to the surface. Minerals and salts dissolved in the water are transported to the surface and concentrate there as the water evaporates away. This renders the soil dead and infertile.
Controls on Soil Formation:
water and energy:
Weathering rates are faster in a warm, moist climate.
Plants and Animals
Plants and animals are a source of organic matter (humus) organic acids enhance chemical weathering.
Decomposer micro-organisms (bacteria, fungi) and worms break down organic matter.
Residual Soil - type of bedrock (granite? limestone? sandstone?)
Transported Soil - alluvial soils laid down by water, loess laid down by wind.
Volcanic Soils - parent material lands on top of the soil.
Slope and angle - soil poorly developed on steep slopes and piles up in cracks.
Angle determines sun exposure
soils generally take millennia to develop, but can be eroded away in a few years.
Elemental Geosystems (2nd ed.), by R.W. Christopherson, 1998