Chapter 7: Weathering, Erosion, and Soil

Wind, Water, Glaciers, Gravity
Four main AGENTS (causes) of Erosion
Rill Erosion
Erosion in which water running down the side of a slope carves a small stream channel.
Gully Erosion
Erosion that occurs when the rill channel widens and deepens.
Deposition
Occurs when eroded materials are dropped in another location.
Soil
Loose covering of weathered rock and decayed organic matter overlying Earth’s bedrock that is characterized by texture, fertility, and color and whose composition is determined by its parent rock and environmental conditions.
Humus
Decaying organic matter that enriches the soil, made up of the remains of dead plants and animal waste.
Climate, Topography, Parent Material, Biological Activity, Time
Factors that affect Soil Formation
Climate
A measure of the weather conditions that occur in an area over a long period of time, including the overall temperature and the average amount of precipitation.
Topography
Refers to elevation and includes the slope and orientation of the land, which affects the type of soil that forms.
Parent Material
The source rock that forms the weathered products that make up an area’s soil.
Biological Activity
The activity of organisms, including fungi and bacteria as well as plants and animals, that interact with the soil and affect its composition.
Residual Soil
Soil that develops from parent material which is similar to local bedrock.
Transported Soil
Soil that has been moved away from its parent material by water, wind, gravity, or a glacier.
Soil Profile
Vertical sequence of soil layers containing the A-Horizon, the B-Horizon, and the C-Horizon.
Soil Horizon
Distinct horizontal layer within a soil profile.
Soil Texture
The relative proportions of particle size that determine a soil’s capacity to accept and retain (hold) moisture.
Soil Fertility
A measure of how well a soil can support the growth of plants.
Legumes
Plants, such as beans and clover, that are useful in agriculture because they allow bacteria to grow on their roots and replace nitrates in the soil.
Crop Rotation
Method used by farmers to retain or restore soil fertility by growing different types of crops in their fields each year.
Munsell System of Color Notation
Used by scientists to describe soil color, and consists of three parts: hue (color), value (lightness or darkness), and chroma (intensity).
Mollisols
Prairie/Grassland soils [visual for “mol”: a “mole” in a grassy field]
Alfisols
Woodland soils [visual for “f”: a forest full of trees]
Entisols
New, young soils [visual for “n”: the word “new”]
Ultisols
Older, mature soils [visual for “ulti”: the “ultimate” age]
Weathering
Chemical or mechanical process that breaks down and changes rocks on or near Earth’s surface and whose rate is influenced by factors such as precipitation and temperature.
Surface Area, Climate (Temperature & Precipitation), Topography (Slope of the Land), Rock Type & Composition
Factors that affect the Rate of Weathering
Surface Area
A measure of how much of the outermost portion of a substance is exposed to its surroundings, making it available to react with other chemicals in the environment.
Mechanical Weathering
Process that breaks down rocks and minerals into smaller pieces but does not involve any change in their composition.
Chemical Weathering
Process by which rocks and minerals undergo changes in their composition due to chemical reactions with agents such as acids, water, oxygen, and carbon dioxide.
Erosion
The removal and transport of weathered materials from one location to another by agents such as water, wind, glaciers, and gravity.

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