Weathering and Soil

Weathering Weathering: breaking down of rocks, soil and minerals as well as artificial materials through contact with the Earth's atmosphere, organisms and water. Two basic types Physical/mechanical Chemical

Physical/Mechanical Frost/Ice wedging Water seeps into open spaces and freezes. Expansion of water wedges and cracks material Breaks at distinct angles

Physical/Mechanical Exfoliation also known as unloading, overlying materials (not necessarily rocks) are removed (by erosion, or other processes) which causes underlying rocks to expand and fracture parallel to the surface

Physical/Mechanical Plant roots seedlings sprouting in a crevice and plant roots exert physical pressure Provide a pathway for water and chemical infiltration. Paper beats rock 

Physical/Mechanical Abrasion mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. moving particles dislodge loose and weak debris from the side of the rock.

Chemical Weathering Oxidation: Materials react with Oxygen from atmosphere or water (H2O) Most common Iron (Fe) “rusting”

Chemical Weathering Hydrolysis(water): Materials react with water to form new material Water dissolves rock Chemicals in water react

Chemical Weathering Reactions Dissolution: Acid dissolved in water dissolves rock Reactions carbon dioxide + water → carbonic acid CO2 + H2O → H2CO3 carbonic acid + calcium carbonate → calcium bicarbonate H2CO3 + CaCO3 → Ca(HCO3)2

Chemical Weathering Plant Acids: Some plants produce weak acids that seep into rocks and dissolve certain minerals Examples : Lichens and Mosses

Question What type of chemical weathering process produces corrosion and iron oxide? Oxidation Times up! Timer

Factors that influence weathering Rock Composition Climate Very cold( no change) Slow weathering Polar regions Dry and Hot Desert regions Moderate (warm summer/cold winter) Fast weathering Temperate regions Rocks are made of minerals Tougher the mineral the slower the weathering Surface area More area exposed to weathering forces, faster the weathering

Surface area and speed of weathering

pH scale

Lower pH = more H+ ion (acidic) pH concentration “power of Hydrogen” Lower pH = more H+ ion (acidic) Higher pH= less H+ more OH- ion (basic or alkaline) 1 x 10 – pH =Concentration

Lab analysis 1 x 10 -2.5= .003 1 x 10 -6.5= .0000003 Or 6.5-2.5=4 .003/.0000003= 10000 times more concentrated Or 6.5-2.5=4 104 =10000

The dirt on dirt (soil) Bedrock: Regolith: Solid un-weathered rock below the surface Regolith: layer of loose, weathered material covering solid rock.(bedrock)

Components of Soil Minerals Water Gases 5% organic matter: 45% weathered rock Rocks are made of minerals Water 25% water Gases 25% Air 5% organic matter: Mostly humus

Weathering and soil formation Explain the relationship between weathering and soil formation. Weathering and erosion make soil

Soil profile Soil profile: Cross section, shows layers top to bottom O. Organic materials Topsoil (organic material) Subsoil minerals collect Regolith R. bedrock

Activity

Answers Tropical climate: Desert: Arctic: Rain and High temperatures cause thick infertile soils to develop. Desert: Low precipitation causes thin soil Arctic: Slow weathering creates thin soil

Explain why temperate climates are ideal soil producing regions. Explain why the study of soil is important for everyone (not just farmers).

Composition of soil Sally Shoppingcart has a sample of soil. After separating the sample she has 40 grams of silt, .04 kg of sand and 20,000mg of clay. Convert all samples to the same units and find percentage of each component in the total sample.

Soil triangle