Geology Unit 6- Weathering and Soil

Weathering

physical breakdown or chemical alteration of rock at Earth’s surface

mechanical weathering

disintegration and physical forces break rock into pieces. increase in surface area

chemical weathering

decomposition and transformation of rock into one or more new compounds. weakens outer rock and allows for mechanical weathering

erosion

removal of weathered rock

Frost wedging

water in cracks freeze, expand, and enlarge cracks in rock

Salt crystal growth

sea spray ends in crevices and pores, the water evaporates and salt crystal form. this pushes apart rock cracks

jointing

fractures with no movement. allows water to penetrate and weathering starts

sheeting

reduction of pressure leads to splitting of slab-like rock (exfoliation dome)

Biological activity

activity of organisms that weather rock. includes burrowing animals and decaying organisms that release acid

water

__ is the most important agent in chemical weathering

1. Oxidation

2. Dissolution

3. Hydrolysis

3 ways of chemical weathering

Oxidation

removal of one or more electron that is lost to oxygen. this decomposes dark materials, leading to rust. Occurs only after iron is freed

Dissolution

minerals are dissolved in water. when water has other minerals, it leads to a chemical reaction (acid rain and hard water).

Hydrolysis

silicates are altered by reacting with acids and water. hydrogen attacks and other ions leave, becoming available for plants or other minerals

Attractors

What rock types that rocks naturally tend to develop into (shale, sandstone, limestone_

Granite

breakdown of clay minerals (high % of inorganic material in soil). eventually settles on seafloor and becomes shale.

Spheroidal

weathering produces spherical shapes from an initial blocky shape. Once already spherical, size changes, not shape

1. Rock characteristics

2. Climate

What influences rate of weathering

Rock characteristics

Composition, solubility, spacing of joints, size of mineral grains

Climate

temperature and precipitation

differential weathering

variation in weathering

Interface

Boundary where all parts of a system meet

Regolith

layer of rock and mineral fragments produced by weathering

Soil

portion of regolith that supports growth of plants

Humus

half is remnants of animal, plants, and decomposed rock, other half is pore spaces with water/air

proportions of particle size, how much water it retains, and how well plants grow

Soil Texture is based on the

Clay, Silt, Sand

Soil textures from smallest to largest

parent material

source of weathered mineral matter where soils develop, residual and transported

Climate

most influential on soil formation, also depends on plants and animals present and materials removed by surface erosion

Plants and animals

furnish organic material, it is rare that soil lacks these completely. Hastens weathering

Bioturbation

worms mixing and enriching soil

less

as time increases, parent material becomes __ significant

topography

length and steepness affect erosion and water contact. optimal is a flat upland surface. slope affects how much sunlight the soil recieves

soil profile

vertical section through a soil showing horizons and parent material

O Layer

mostly organic matter, loose leaves, and lower part of humus. microscope organisms contribute oxygen and CO2. part of topsoil

A Layer

mineral matter, less than 30% humus. part of topsoil

E Layer

light colored, little organic material. zone of elutriation (washing out fine soil) and leaching

B Layer

materials is deposited from E layer, known as zone of accumulation as fine particles hold water. known as the subsoil

C Layer

layer where parent material is still identifiable, still regolith

Soil Taxonomy

Classification system with 6 categories based on observable characteristics

Productivity index

how well soil is able to grow crops, rated on scale from 0-19

can become severely leached, and accelerates soil erosion as protective vegetation is gone.

How do destruction of tropics affect soil?

No Till

crop residues left on fields, good for productivity