W1 Weathering + soil formation

rock vs mineral

Rock - A relatively hard, naturally occurring mineral material. can consist of a single mineral or of several minerals that are tightly compacted or held together by a cement-like mineral matrix.

Mineral is a naturally occurring, inorganic substance with a definite chemical composition and a regular crystalline structure.

weathering

breakdown and changes in rocks and minerals at or near tEarth's surface that lead to formation of soils.

physical weathering

breaking apart without change in their chemical composition.

examples of physical weathering

External pressure, changes in temperatures, water and ice

CHEMICAL WEATHERING

changes of chemical composition of rocks and minerals, which can result in either (a) weakening of crystalline structure of minerals, or( b) complete destruction of the crystalline structure.

chemical weatehering processes

• hydration

• carbonation

• hydrolysis

• oxidation reduction

• dissolution ( or solution)

examples of the chem weathering processes

• Hydration

  • Water molecule attaches to mineral

• Hydrolysis

  • Water molecule splits and the H associates with the mineral

• Dissolution ( solution)

  • Water molecule surrounds the anion and cation and separates them

• Carbonation

  • Co2 + water = carbonic acid, which is weak acid in the soil that enhancines weathering process

• Oxidation-reduction 

  • change in valence and ionic radius causes destabilizing adjustments in the crystal structure of the mineral, weakening that structure and making it more susceptible to other processes of chemical weathering

  • Commonly minerals involving Fe, Mn, and S susceptible to this reaction

climate factor of soil formation

•  influences through precipitation and temperature - control weathering rate

  • p = increases weathering rate

    • amount of clay increases with P

  • T=increases chemical rxns and stimulates bilogical activity ( bioloical weathering)

biological weathering

caused by various actions of plants, animals and microorganisms.

• It can be done through release of acid forming chemicals that cause weathering, or through the breaking down of rocks  by wedging roots, or by transfer and mixing of materials by burrowing animals.

biological weathering example - lichens

fungal component produces series of organic acids, called lichen acids, that aid in the chemical breakdown of the minerals that make up the rock

Parent material -factor

• Uncolsidated and more or less unchanged mineral and organic material which soils are developed by

• Influences the mineral composition of the soil

time

• Influences the amount of weathering that takes place

•  controls how far soil development has progressed and how different the soil has become from the underlying parent material. 

biota/organisms- factor

• influcence amoutn of OM in soil

• responsible for mixing and moving soil material

• contribute to weathering

How does topography affect soil development?

• Slope

can have different erosion and accumulation of nutrients and sediments

• dominat erosion = upper and steepest portion of slope

• accumulation greates in = lower and flatter portion of landscape

  • top of slope = shallow soils, crest of slope = deep soil

How does topography affect soil development?

• Aspect

• S = more sun = drier and warmer

  • Soil development higher as long as not too dry- water needed!

  • Thicker soil

• N= less sun = cooler and wetter

  • slower/less development with lower E input

  • chemical weathering is less pronounced

  •  thinner soil

How does topography affect soil development?

• elevation

climate becomes cooler and wetter as elevation increases from valley bottoms to mountain tops.

1. Briefly discuss how climate and topography are interrelated in terms of soil formation.

• climate refers to the percpertiaton and temperature of an area, that control the amount of water and solar E that affect soils.

• Topography refers to aspect, slope and elevation. These properties influence soil development by controlling the distribution of water in the landscape, the amount of sun received

  • controlling the extent the climatic factors have on a soil

topogrpahy, soil forming factor

based on slope, aspect and elevation, influences soil development by controlling distrobution of water, sun recived and suscpetibility to erosion