1. 5.2 Soil

2. Characteristics of Soil
Soil is the part of the regolith that supports the growth of plants
Regolith covers nearly all of the Earth’s land surface
Composition
Texture
Structure

3. Characteristics of Soil continued…
Composition
Structure
4 main components
Mineral Matter
Broken down rock
Organic Matter
Humus (decay remains)
Water
Air
Soil particles usually form clumps that give soil a certain structure
Determines how easily it can be cultivated & susceptible it is to erosion
Affects how water penetrates the soil

4. Characteristics of Soil continued…
Texture
Refers to the proportions of different particle sizes
Based on the % of clay, silt, & sand in soil
Influences the ability to support plants.
Sandy soils = drain & dry out quick
Clay-rich soils = drain slow
Loam soils = best for plant growth & retain water best

5. What type of soil consists of 10% clay, 60% silt, 30% sand?

6. Soil Formation Most important factors of soil formation are
Parent Material
Time
Climate
Organisms
Slope

7. Soil Formation Parent Material Source of the mineral matter in soil
How does PM influence soil
Source of the mineral matter in soil
Soil that forms on bedrock is called residual soil
Soil that forms on unconsolidated deposits is called transported soil
Look at fig. 12 pg. 135
2 ways
Chemical Makeup
Affects soil’s fertility ( types of plants the soil can support)
Rate of Weathering / Rate of Soil Formation
Unconsolidated deposits = partly weathered (more SA)
TS develops more quickly than RS

8. Soil Formation continued…
Time / Climate
Organisms / Slope
Longer forming = thicker
Climate has greatest effect on soil formation
Temp.
Amt. of Precipitation
Types of organisms in the soil
Plants are main source of organic matter
Animals & microorganisms also contribute
Fungi, bacteria (help to decompose)
Variations in slope = different soil types

9. Soil Profile
Soil varies in composition, texture, structure, & color at different depths
Soil horizons (Surface > A > B > C > PM )
Soil Profile (all the soil horizons)
A Horizon
Topsoil, mainly organic matter (ex. Loose leaves). Lower part of A is a mixture of mineral matter & organic matter
B Horizon
Subsoil, Fine clay particles, Lower limit of plant roots & burrowing animals
C Horizon
Partially weathered parent material. Resembles PM

11. Soil Types 3 common types of soil are pedalfer, pedocal, & laterite
Pedalfer usually forms in temperate areas with > 63 cm of rain each year (Eastern USA – forested areas)
Pedocal are found in drier western USA (Grasses & brush vegetation)
Laterite form in hot, wet tropical areas (Deeper in the soil) (When dried = very hard & waterproof)
Soil in tropical rainforests lack nutrition
Garden in TRF or TN?

12. Soil Erosion Water, wind, & other agents move soil from place to place
Rain
Human activities that remove natural vegetation (farming, logging, construction) have greatly accelerated erosion
Depends on soil characteristics, climate, slope, & vegetation
Wind erodes soil more slowly than water
Ex) 1930s Dust Bowl

13. Soil Types are determined primarily by the climate of where they form.
Location
Contains
Color
Pedalfer
Temperate, wet
Eastern US
Iron oxide, aluminum clays
Red-brown
Pedocal
Dry
Western US
Calcite
Gray-brown
Laterite
Hot, humid
Tropics
Iron oxide, aluminum oxide
Orange red

14. 5.3 Mass Movement

15. Triggers of Mass Movements
The transfer of rock & soil downslope due to gravity
Saturation of surface materials w/ H2O, slopes, removal of vegetation, earthquakes
Earthquakes
Dramatic triggers – aftershocks - landslide
Removal of Vegetation
Plants = more stable slopes due to root systems binding soil & regolith (Ex. Landslide)
Oversteepened Slopes
MM become more likely when a slope > 40 degrees
Water = heavy rain / rapid melting of snow
Ex) Mudslides / Mudflows

16. Types of Mass Movements
Classified based on the kind of material that moves, how it moves, & the speed of movement
Rockfalls
Rocks/rock fragments fall freely through air (steep slope)
Slides
Rockslides
Slumps
Downward movement of a block of material along a curved surface – slower travel speed
Flows
Mudflows - Earthflows
Creep
SLOWEST type of MM (few mm/cm per year) Ex. Freeze-thaw cycles