1. Weathering
Essential Vocabulary

2. Weathering & Natural Erosion
weathering – the processes that breaks down rocks, soils, or minerals at Earth's surface. Types of weathering are mechanical and chemical.
mechanical weathering – type of weathering where rocks are physical broken down into smaller pieces.
chemical weathering – process that breaks down rock through chemical changes
Good to Know
Weathering and erosion work together continuously to wear down and carry away rocks at the Earth’s surface.
Geologists make inferences based on the principle of uniformitarianism. That is a big word that means the same processes that operated today operated in the past.
This means that, over time, even the biggest, hardest rocks are broken down by weathering.

3. How to Know Mechanical Weathering When You See It?
Weathering & Natural Erosion
abrasion – the grinding away of rock by rock particles carried by water, ice, wind, or gravity.
How to Know Mechanical Weathering When You See It?
Good to Know
The causes of mechanical weathering include freezing and thawing, release of pressure, plant growth, actions of animals, and abrasion.

4. ice wedging – process that splits rock when water seeps into cracks, then freezes and expands.

5. Weathering & Natural Erosion
release of pressure– as erosion removes surface material, pressure is reduced on the rock, causing outer sheets to flake off (like onion layers)
animal actions – burrowing animals (moles, gophers, prairie dogs, and some insects) loosen and break apart rocks in the soil.
Good to Know
The causes of mechanical weathering include freezing and thawing, release of pressure, plant growth, actions of animals, and abrasion.

6. plant growth
trees (and other plant) roots enter cracks in rock and force it apart as the roots grow and expand

7. The rate of weathering increases as more and more of the rock’s surface area is exposed.

8. Weathering & Natural Erosion
water – most important cause of chemical weathering, because water dissolves rock.
oxygen – the process when iron combines with oxygen when water is present is called oxidation (rust)
Good to Know
The causes of chemical weathering include the actions of water, oxygen, carbon dioxide.

9. Weathering & Natural Erosion
Good to Know
The causes of chemical weathering include the actions of water, oxygen, carbon dioxide.
This creates holes or soft spots in rock, which helps with breaking down the rock.
carbon dioxide – in the atmosphere, CO2 combines with rainwater. In soil, it becomes carbonic acid that easily weathers marble and limestone.

10. Weathering & Natural Erosion
living organisms – lichens grow on rocks and seeds sprout in cracks to produce weak acids.
Good to Know
The causes of chemical weathering include the actions of water, oxygen, carbon dioxide.
This creates holes or soft spots in rock, which helps with breaking down the rock.

11. Weathering & Natural Erosion
Good to Know
The causes of chemical weathering include the actions of water, oxygen, carbon dioxide.
This creates holes or soft spots in rock, which helps with breaking down the rock.
acid rain – chemicals (sulfur, carbon, and nitrogen compounds) from air pollution mix with water vapor forming acids that fall with raindrops.

12. Rates of Weathering
climate - the average weather conditions, including temperature, precipitation, and wind, most often occur in a particular region.
Good to Know
Some kinds of rocks weather more rapidly than others
The most important factors that determine the rate at which weathering occurs are the type of rocks and the climate.

13. permeable – material is full of tiny, connected air spaces that allow water to seep through it.
Rates of Weathering
Good to Know
Some kinds of rocks weather more rapidly than others
The most important factors that determine the rate at which weathering occurs are the type of rocks and the climate.
Rocks that dissolve in water will weather faster than rocks that do not dissolve in water. Chemical weathering happens faster at high temperatures. Both chemical and mechanical weathering happen faster in wet climates.

14. The End Products Of Weathering
Weathering breaks down rocks into particles of many sizes (clay, silt, sand, pebbles, cobbles, boulders)
Soil is a mixture of rock and organic material.
Soils are the result of weathering and biological activity over long periods of time.
A mature soil profile shows three distinct horizons. The A-horizon (topsoil) is dark and rich in humus.
The B-horizon (subsoil) is lighter in color, has more clay, and less humus.
The C-horizon is made of slightly weathered bedrock (rock fragments). Beneath the three horizons is the unweathered bedrock.
Soils may be residual (form from underlying bedrock) or transported (form from sediments that have been carried from some other place).

15. Different Climates, Particle Sizes, Composition & Exposure Affects the Weathering Process
At high latitudes and high altitudes, where it is cold and humid, frost action is the major form of weathering.
In warm and humid climates chemical weathering is most important.
In arid (dry) climates, very little weathering takes place.
Local climatic conditions (winds, nearness to cities, etc.) can affect the of weathering.
Small rock particles will weather faster than a single large sample of the same mass because more surface area exposed by the small particles.
Rocks containing more resistant minerals will weather at a slower rate.
Rocks that are not exposed to the atmosphere and hydrosphere will weather at the slowest rate.

16. It's a Hard Rock Life