Download Rocks & Weathering Notes: Chapter 8 o Cold

Rocks & Weathering Notes: Chapter 8
Weathering & Erosion






Weathering is the process that breaks down rock and other substances at Earth’s surface
Factors that contribute to weathering
o Heat
o Cold
o Water
o Ice
o O2 & CO2 in the atmosphere
Examples of weathering
o Rust
o Peeling paint
o Cracking sidewalks
o Potholes
Erosion is the removal of rock particles by water, wind & ice or gravity
Weathering breaks rocks into smaller pieces and erosion takes those pieces away
Two types of Weathering
o Mechanical Weathering
o Chemical Weathering
Mechanical Weathering


Mechanical Weathering is caused by physically breaking rocks into smaller pieces
Causes of mechanical weathering
o Freezing
 Ice Wedging: process where wedges of ice in rocks widen and deepen cracks
o Thawing
o Release of pressure
o Plant growth
o Animals
o Abrasion: grinding away of rock by rock particles carried by erosion
Chemical Weathering


Chemical Weathering is the process that breaks down rock through chemical changes
Causes and effects of chemical weathering
o Action of water
= dissolves rock
o O2 (Oxygen Gas)
= oxidation (rust)
o CO2
= dissolves in rain water and forms carbonic acid
o Living organisms = plants grow and produce a weak acid
o Acid Rain
= compounds from burning fossil fuel to mix chemically with rain to form
acid
Weathering


Mechanical weathering breaks rock and makes more surface area for chemical weathering to
take place
Rate of weathering affected 2 ways
o Rock type
 More permeable allow more water to seep inside
o Climate
 Mechanical weathering occurs faster in wet climates
 Chemical weathering occurs faster in hot temps
 Weathering occurs more rapidly in a warm rainy climate
Soil





Soil is the loose weathered material on the earth’s surface
Main ingredient: bedrock
o Bedrock: solid layer of rock beneath soil
Composition of soil
o Rock particles
o Minerals
o Humus: dark colored substance that is plant and animal matter decay
o Water
o Air
Fertility of Soil: measure of how well the soil supports plant growth
Texture of Soil
o Depends on size of individual soil particles
 Largest: Gravel
 Sand
 Silt
 Clay
o Texture is important for plant growth
 Clay holds too much water
 Plants drown
 Sandy soil drains quickly
 Plants die from too little water
 Loam: best type of soil for growing plants
 Soil that is made of equal parts of sand and clay
Soil formation


Soil forms as rock is broken down by weathering and is mixed with other materials on the
surface.
Soil Horizon: a layer of soil that differs in color and texture from the layers above and
below it.
o Horizon A: Topsoil which is a crumbly dark brown soil mixture of humus, clay, other
minerals
o Horizon B: clay and other particles washed down from horizon A
 Also called subsoil


o Horizon C
 Only weathered rock
Factors that affect soil formation
o Climate
 Soil formation quickly forms in a warm rainy climate
o Type of rock
 Limestone forms soil more quickly
Soil Classification
o Climate
 Thick soil: Moderate Temp
o Plants
 Grassland soil is different from forest soil
o Soil Composition
 rocky
 sandy
 clay
Living Organisms in Soil


Make humus (formed from decomposition)
o Litter: a loose layer of dead plant leaves and stems on the surface of the soil.
o Decomposer: organisms that break down the remains of organic material
 Bacteria
 Worms
 Fungus
 Small animals
Mix soil
o Makes space for air and water
Soil Conservation





Soil Conservation: The management of soil to prevent its destruction
Type of Soil Conservation
Contour plowing
Conservation plowing
Crop rotation