Soils Geomorphology Pedology and Soil Geomorpholgy

Soils Geomorphology 

Bruce Herbert 

Geology & Geophysics 

EG: Pedology 

Pedology and Soil Geomorpholgy 

 

 

Pedology: the science devoted to understanding how soils 

developed, relationships to environment, and their geography 

Soils: why are they unique 

-Hans Jenny: soils unique because they represent the “meeting 

ground” between the atmosphere, lithosphere, biosphere, and 

hydrosphere 

 

Soils are dynamic,especially under conditions of changing 

climate and vegetation 

EG: Pedology

Soils: Definitions 

 

 

 

Unconsolidated material overlying 

bedrock (geologist) 

Can dig with hand tools (engineer) 

Transported 

Residual 

Ability to support plant growth 

(pedologist) 

Houston Black - Texas State Soil 

http://soils.usda.gov/ 


Soil Terms 

 

 

 

Pedon: a soil individual 

whose size is about 1 

m 2 , but whose 

boundaries are often 

hard to define 

Soil Profile: sequence 

of layers, or horizons, 

from the land surface 

which are distinct in 

physical and chemical 

characteristics 

Parent Material: the 

earth materials in which 

the soil develops. At 

beginning, soils tend to 

be little altered parent 

material 

Soil profile - in Jemez Canyon, NM 

http://www.glorietageo.com/images.html 


Soil Terms 

 

 

 

 

Horizons: unique layers: the eluvial 

horizon, the illuvial horizon 

Eluviation: removal of materials 

chemically, with changes chemical 

changes in movement. 

Illuviation: deposition of chemically 

altered materials in lower horizon 

Translocation: movement without 

chemical alteration 

http://www.cst.cmich.edu/users/Franc1M/esc334/images/origin%20of%20soil/profile.gif 


Soil Maps 

Brazos County Generalized Soil Map 

http://soils.usda.gov/survey/online_surveys/texas/ 


Soil Profile (Master Horizons) 

 

 

 

 

 

 

 

O—mostly partially decomposed organic 

matter 

A—mineral and organic horizon 

E—loss of clay, Fe, Al, organics (eluviation) 

B horizon of accumulation (illuviation) 

Clay—argillic 

Sodium—natric 

Fe + Al—spodic 

C—partially weathered parent material 

(unconsolidated or consolidated) 

R—rock 

K—calcium carbonate 


Soil Characteristics: Physical 

 

 

 

Structure: how peds are arranged. 

Particle Size/grain size = amount of sand, silt, clay in soil. 

Determines reactivity, permeability, bearing strength, etc. 

Types of horizons present, their thickness, total depth of soil profile 

Soil colloids tend to 

clump together into 

larger particles, 

producing the soil 

structure. 

http://www.unc.edu/co 

urses/2005ss2/geog/0 

10/001/Soil%20Format 

ion/Soil%20Formation. 

htm 


Soil 

Characteristics: 

Soil Texture 

The soil texture is a fundamental property of a soil, determining the limits of drainage, water availability 

and fertility. Sandy soils: readily drained, light and easy to work, warms rapidly in spring, chemically 

infertile. Clay soils: easily waterlogged, heavy, stays cool, fertile (many nutrients available). Loam soils:- 

mix of sand and clay soil, usually best for agricultural purposes. These have some ribbon-forming 

properties and tend to feel a bit gritty. They also tend to leave a whitish residue (the silt) on your 

fingers when you rub this type of soil. 

http://www.unc.edu/courses/2005ss2/geog/010/001/Soil%20Formation/Soil%20Formation.htm 


Soil Characteristics: 

Water Holding Capacity 

 

 

 

Available water capacity: 

difference between field 

capacity and permanent 

wilting point 

Field capacity: maximum 

amount of water that can 

be held against gravity 

drainage (adhesion and 

surface tension) 

Permanent wilting point: 

remaining water is so 

tightly held by tension that 

plants cannot extract it. 

http://www.ext.colostate.edu/pubs/garden/gardimg/07754f02.jpg 


Soil Characteristics: Water Holding Capacity 

http://www.cpc.ncep.noaa.gov/soilmst/img/curr.w.full.daily.gif 


Soil Characteristics: Water Holding Capacity 

http://www.cpc.ncep.noaa.gov/soilmst/img/curr.w.anom.daily.gif 


Soil Characteristics: Chemical 

 

 

 

 

 

Color 

red = iron oxide 

black = organic matter, 

maganese oxides 

green-gray = reducing 

pH: soil reaction: whether 

acidic, neutral, or alkaline 

CEC: cation exchange capacity 

Soil organic matter 

Mineralogy, especially in the 

clay fraction 

www.uwsp.edu/.../images/biosphere/soils/ph.jpg 


Soil 

Characteristics: 

Chemical 


Soil Forming Factors 

 

 

 

Five soil forming factors: 

Parent material: weathering, texture, mineralogy 

Time: degree of weathering, sediment movement 

Climate: degree of weathering, biotics 

Organisms: degree of weathering, organic matter accumulation 

Relief: microclimates, hydrology 

Affect soil characteristics 

Comparisons of soils may allow: 

Relative dating; important for reconstructing past sequences of 

geomorphic events 

Estimating past environmental conditions that may have 

influenced geomorphic processes 


Soil Forming Factors: Climate 


Soil Forming Factors: Parent Material 

 

 

 

Resistance of parent 

material to weathering 

Texture 

Mineral stability 

Bowen’s Reaction Series 

Secondary Mineral Formation 


Classification (Soil Taxonomy—USDA) 

Order (12) 

Suborder (63) 

Great Group (319) 

Subgroup (2484) 

Family (8000) 

-- Series (19,000) 

The second edition of Soil Taxonomy, A Basic System of Soil Classification for Making and 

Interpreting Soil Surveys is now available here in PDF format for printing or viewing. 

http://soils.usda.gov/technical/classification/taxonomy/ 

The 9th edition of Keys to Soil Taxonomy is available now in Adobe Acrobat or Microsoft 

Word format. 

http://soils.usda.gov/technical/classification/tax_keys/ 


Major Soil Orders: Spodosols 

The central concept of Spodosols is that of soils in which amorphous mixtures of organic matter 

and aluminum, with or without iron, have accumulated. In undisturbed soils there is normally an 

overlying eluvial horizon, generally gray to light gray in color, that has the color of more or less 

uncoated quartz. 


Major Soil Orders: Alfisols 

The central concept of Alfisols is that of soils that have an argillic, a kandic, or a natric 

horizon and a base saturation of 35% or greater. They typically have an ochric epipedon, 

but may have an umbric epipedon. They may also have a petrocalcic horizon, a fragipan or 

a duripan. 


Major Soil Orders: Mollisols 

The central concept of Mollisols is that of soils that have a dark colored surface 

horizon and are base rich. Nearly all have a mollic epipedon. Many also have an 

argillic or natric horizon or a calcic horizon. A few have an albic horizon. Some also 

have a duripan or a petrocalic horizon. 


Major Soil Orders: Ultisols 

The central concept of Ultisols is that of soils that have a horizon that contains an 

appreciable amount of translocated silicate clay (an argillic or kandic horizon) and few 

bases (base saturation less than 35 percent). Base saturation in most Ultisols decreases 

with depth. 


Major Soil Orders: Aridisols 

The central concept of Aridisols is that of soils that are too dry for mesophytic plants to 

grow. 


Major Soil Orders: Oxisols 

The central concept of Oxisols is that of soils of the tropical and subtropical regions. 

They have gentle slopes on surfaces of great age. They are mixtures of quartz, kaolin, 

free oxides, and organic matter. For the most part they are nearly featureless soils 

without clearly marked horizons. Differences in properties with depth are so gradual that 

horizon boundaries are generally arbitrary. 


Major Soil Orders: Vertisols 

The central concept of Vertisols is that of soils that have a high content of expending 

clay and that have at some time of the year deep wide cracks. They shrink when drying 

and swell when they become wetter. 


Major Soil Orders: Incetisols 

The central concept of Inceptisols is that of soils of humid and subhumid regions that 

have altered horizons that have lost bases or iron and aluminum but retain some 

weatherable minerals. They do not have an illuvial horizon enriched with either silicate 

clay or with an amorphous mixture of aluminum and organic carbon. 


Less Common Soil Orders 

 

 

 

 

Entisols: soils too young to have mature characteristics 

Histosols: organic soils 

Gelsols: soils with permafrost within 100 cm of the surface 

Andisols: immature volcanic soils

Soils Geomorphology Pedology and Soil Geomorpholgy

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