 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
Composition
Structure
 4 main components
 Soil particles usually
 Mineral Matter
 Broken down rock
 Organic Matter
 Humus (decay remains)
 Water
 Air
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
 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
What type of
soil consists
of 10% clay,
60% silt, 30%
sand?
https://www.yout
ube.com/watch?v
=-KNcUNGaou0
 Most important factors of soil formation are
 Parent Material
 Time
 Climate
 Organisms
 Slope
Parent Material
 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
How does PM influence soil
 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
Time / Climate
Organisms / Slope
 Longer forming = thicker  Plants are main source of
 Climate has greatest
effect on soil formation
 Temp.
 Amt. of Precipitation
 Types of organisms in
the soil
organic matter
 Animals & microorganisms
also contribute
 Fungi, bacteria (help to
decompose)
 Variations in slope =
different soil types
 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
 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?
 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
Soil Types are determined primarily by the
climate of where they form.
Soil Type
Climate
Pedalfer
Location
Contains
Color
Temperate, Eastern
wet
US
Iron oxide,
aluminum
clays
Redbrown
Pedocal
Dry
Western
US
Calcite
Graybrown
Laterite
Hot, humid
Tropics
Iron oxide,
aluminum
oxide
Orange
red
 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
 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