Soil Geomorphology

A Syllabus on
Soil geomorphology (geopedology)
In the framework of Landscape Ecology
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Contrary to what is sometimes thought geopedology is not only an imageinterpretation map, with a tabulated legend wherein map units are described
in geomorphologic terms, or a well organized application of geomorphology
to soil survey. Geopedology is a conceptual approach, which fortifies a
scientific framework for soil resource inventory and its interpretation/
evaluation for various uses. In other words, it is a science and, at the same
time, an art of modelling the occurrence of soils in landscape, a process
which is based on (mental) integration of knowledge on climate, geology,
geomorphology, sedimentalogy, hydrology, vegetation, and pedology. A
geopedologic map is a soil map, which includes much facts and
understanding about the landscape (Farshad et al., 2005a).
Dr. Abbas Farshad
Earth Systems Analysis Dept.
ITC, Enschede
The Netherlands
[email protected]
Aug. 2006
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List of content:
A Few Definitions
Introduction
Soils on the landscape:
Soil formation and development
A. forming factors
B. forming processes
Soil material
A. Organizational levels
B. Properties
C. describing soil profiles
D. soil classification
Soil resource inventory or soil survey
1. Introduction
2. Importance of geomorphology for soil survey
3. Implementing geomorphology in soil survey
4. Structure of the taxonomic system
5. The proposed system by Zinck (1988)
Geoforms systematics
Application of soils to physical and environmental studies
How far are we with digital soil mapping
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Definitions:
Soil: The naturally occurring 3-D unconsolidated material on the earth’s crust that has
been influenced by parent material, climate, macro and micro organisms, and relief, all
acting over a period of time to produce soil that may differ from the material from which
it was derived in many physical, chemical, mineralogical, biological, and morphological
properties.
Atmosphere: The air surrounding the earth, thickness of which is roughly put at
200km.
Biosphere: The part of the earth where living organisms are found, and with which
they interact to produce a steady-state system, effectively the whole planet ecosystem.
Hydrosphere: The total body of water which exists on or close to the surface of the
earth.
Lithosphere: The upper layer of the solid earth, comprizing all crustal rocks and the
brittle part of theuppermost mantle.
Pedosphere: The envelope of the earth where soils occur and where soil-forming
processes are active.
Landscape: All the natural features that distinguish one part of the earth’s surface
from another part. Usually, it is the portion of land or territory that the eye can see in a
single view, including all its natural characteristics.
Ecolology: Ecology refers to the study of living (microbes, plants, animals and
humans) and non-living components (the physical environment) as a whole. The word
ecology is stemmed from the Greek word meaning “house”.
Landscape Ecology: The study of environmental factors and interactions at a
scale that encompasses more than one ecosystem at a time.
Introduction
Soil is a complex 3-D object, the X and Y dimensions (its surface) of which can be
observed, if not covered by vegetation and/or other objects, whereas the Z dimension (its
depth) is not visible, hence quite difficult to describe and/or map it, in order to know its
distribution, which is often required for (land use) planning purposes, and, in some cases,
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for serving the needs of geomorphologists, environmental geologists, and archaeologists
working in Quaternary research (Birkland, 1999).
Considering the facts:
- that soil is the product of the actions of climate, flora and fauna, and topography
(relief) on rocks/ sediments in spans of time, the soil variability, both in lateral as
well as vertical directions, has always been (and remains) a complex issue, and
- that with the introduction of the physiographic (holistic) school, which was later
on also fortified by (the use of) aerial photo-interpretation, the role of
geomorphology was intensified,
soon it became clear that the problem of variability can be, to a great extent, solved by
applying geomorphology.
Through mapping landform, which are also 3-D, we have actually map soils, as soil is an
integral part of the landform. With this argument soil-landform relationships become
important to soil surveyors.
Whether we should use the term soil geomorphology in the same way as we use the terms
soil structure, soil texture, soil pH, etc, may be questionable to some people. Does the soil
have geomorphology, in its strict literal sense (see the definition)?
Geomorphology (geo=earth, morph=shape and logy=survey) is a branch of geology
dealing with the form of the earth, the general configuration of the earth surface, and the
changes which take place, that is, parallel with the evolution of landforms.
Let us for a while ask ourselves, once again, the question of “what are we actually
looking for?” Isn’t geomorphology a tool to help us detect the third dimension of the
soil? Would the terminology then be satisfactory? Or, “the application of geomorphology
to soil science” (Gerrard, 1992) is a better terminology? What about when soils data are
used by geomorphologists, environmental geologists, and all others who work in
Quaternary geology, and other disciplines? Aren’t we all working for landscape? What is
landscape, and what are the components of landscape ecology? (see also Huggett, 1995).
As it is noticed, these notes started with the title “soil (land)scape study”!! we would
come back to this, preferably at the end of the course, to listen to everyone’s suggestion
on an appropriate title, i.e., one of the followings:
- Soil geomorphology
- Geopedology
- Soils and geomorphology
- Applied geomorphology to soil science
- Physiography and soils
- Soil (land)scape study; within the landscape ecology framework (IALE=
http://www.crle.uoguelph.ca/iale/)
Landscape ecology is the study of spatial variation in landscapes at a variety of scales. It
includes the biophysical and societal causes and consequences of landscape
heterogeneity. Above all, it is broadly interdisciplinary.
The conceptual and theoretical core of landscape ecology links natural sciences with
related human disciplines. Landscape ecology can be portrayed by several of its core
themes:
. the spatial pattern or structure of landscapes, ranging from wilderness to cities,
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. the relationship between pattern and processes in landscapes,
. the relationship of human activity to landscape pattern, process and change,
. the effect of scale and disturbance on the landscape.
Soils on the landscape
Soils are dynamic, natural bodies in the landscape and evolve over time. The first stage of
development is weathering (physical, chemical and biological) of bedrock to form
unconsolidated rock fragments, the parent material. This is the bed where soil will form
in, that is, the formation of horizons (known as horizonation). Horizonation is taken care
of by pedogenic processes, whereas geogenic processes (e.g., sedimentation) are
responsible for lateral variation. If, instead of rock, a thick layer of sediments is the
parent material, soil formation is one step ahead, as there will be no need that the
consolidated rock is first fragmented/weathered, converting into unconsolidated material
(regolith/ saprolite). However, mineral stability (that is resistance to weathering) is the
issue here (e.g., zircon> garnet> quartz> muscovite> feldspar> augite> biotite> volcanic
glass>olivine).
The concept of soil as a natural body integrating the accumulated effects of climate and
vegetation acting on surficial materials was first introduced by Dokuchaev, in Russia,
around 1870. The further development of the concept was followed by other Russian
scietists and later on by Europeans such as Glinka (1914) and soon after used by
Americans, who were involved in the development of soil classification (e.g., the one
published in 1938).
Knowing that soils cover the uppermost of the earth’s surface (composed of various types
of rocks, sediments, etc), grading, with depth, into parent material (or rock) and into other
soils laterally, a large diversity of soils can be expected on earth, which to a great extent,
are controlled by landforms, considering the fact that the same forming factors (climate,
vegetation, parent rock, etc) responsible in the formation of landforms, control also the
formation of soils. Therefore, in order to solve a number of ecological, environmental,
agricultural and forestry problems, an approach of using the relationships between pedons
and landscapes (units) is highly desirable and effective.
It would be appropriate to briefly look into what the soil, being composed of solid, liquid,
air and water, does for us :
• Soil provides a physical matrix, chemical environment, and biological setting for
water, nutrient, air, and heat exchange for living organisms.
• Soil controls the distribution of rainfall or irrigation water to runoff, infiltration,
storage, or deep drainage. Its regulation of water flow affects the movement of
soluble materials, such as nitrate, nitrogen or pesticides.
• Soil regulates biological activity and molecular exchanges among solid, liquid,
and gaseous phases. This affects nutrient cycling, plant growth, and
decomposition of organic materials.
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•
•
•
Soil acts as a filter to protect the quality of water, air, and other resources.
Soil provides mechanical support for living organisms and their structures. People
and wildlife depend on this function.
Soil is the history book of the landscape (see the attached article on climate
change)
Soil formation and development
A. Soil forming factors:
In an undisturbed ecosystem, the following factors play a role in the formation of soils:
climate ( C ), vegetation (V), topography or relief (R), parent material (P), and organisms
(O), over a period of time (T)
This is what Jenny (1941) stated in the following equation, already in 1941:
S= f (C,V, O, R, P, T,…)
(This section will be explained in detail, consulting the text on http://www.
pedosphere.com)
B. Soil forming processes:
A soil forming process is a complex or sequence of reactions and recognization of matter
occurring under the control of a contination of soil forming factors and leading to a given
arrangement of soil material in a profile (Zinck, 1988).
In a simplified soil forming model, a soil is considered as an open system on which four
main types of processes act:
a. Additions to a soil body:
- heat from solar radiation
- water from rainfall and/or groundwater
- organic matter from vegetation of fertilization
- sediments from flooding
- soluble compounds from flooding or fertilization
b.
-
Losses from a soil body:
heat to the atmosphere
water by runoff, hypodermic flow and/or deep percolation to groundwater
organic and mineral materials by erosion
soluble compounds by erosion and deep leeching
c.
-
Transformation of material within a soil body:
decomposition of organic matter
weathering of primary minerals
neoformation of clay minerals
formation of clay compounds, concentrations and cementations
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-
formation of soil structure by biological construction or physico- chemical
partition
d. Translocation within a soil body:
- downwards migration (illuviation) of clay, salts, carbonates, organic matter,
sesquioxides
- upwards migration of salts
- lateral migration of soluble compounds.
Buol et al (1980) give a list of processes, a few of which are copied here:
- Eluviation: Movement of material out of a portion of a soil profle as in an albic
(e.g., in Spodosols) horizon
- Illuviation: Movement of material into a portion of soil profile as in an argillic
(e.g., in Alfisols) horizon
- Salinization: The accumulation of soluble salts such as sulfates and chlorides of
calcium, magnesium, sodium, and potassium in salty (salic) horizons
- Podzolization: The chemical migration of aluminium and iron and/or organic
matter, resulting in the concentration of silica in the layer eluviated
- Etc (please refer to Buol et al, 1980)
In short, once the soil material (regolith) is settled, soil forming processes (additions,
losses, translocation, and transformation) will start acting. Though, very difficult to say
about the type of the process, which would act, depending on the intensity and on the
dominant role of the soil forming factor (e.g., lithofunctional, topofunctional, etc) one or
several process(es) will act to further develop the soil.
Soil material
A- Organizational levels (Zinck, 1988):
1.Nanolevel.… (elements, molecules, particles)
2.Microlevel… (soil aggregates)
3.Mesolevel... .(soil horizon)
4.Macrolevel... (pedon)
5.Megalevel….(polypedon)
A.Farshad,ITC
1. Nanolevel:
-units of measurement: nm, µm (and mm)
-nature of material : elements, molecules, particles
-means of observation : electron microscope, X-ray diffraction
-nanolevel is the level of basic soil material reactions, which can be either :
-chemical, -Physico-chemical, or -micro-mechanical
•
Chemical reaction can be by solubility, where chemical compounds change:
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-Solution (salts) :
-Carbonation (carbonates):
-Hydrolysis (silicates):
NaCl + H 2 O --- H 2 O + Na + Cl
CO 2 + H 2 O --- H CO 3 + H
Ca CO 3 + (H CO 3 + H)--- Ca (HCO 3 ) 2
KAl Si 3 O 8 + HOH--- HAl Si 3 O 8 + KOH
Chemical reaction can also lead to changes of the structure of minerals (oxides), such as
in the following processes:
-Hydration
-Oxidation and reduction
• Physico-chemical reactions: when clay and organic matter take care of forming
good soil aggregation (resistance to erosion); or different cations exchanging at the clay
particle edge, that is, cation exchange capacity (fertility)
Farshad,ITC
• Micro-mechanics
- Packing types (for sand and coarse silt grains)
- Fabric types (for clay and fine silt)
* Defloculated (risk of mudflow)
* Dispersed (risk of solifluction)
* Aggregated (risk of landslide)
* Flocculated (soil stability)
2. Microlevel :
That is at the aggregate level, where micromorphologic (by means of petrographic
microscope) study are involved (Brewer, 1994; Bullock et al., 1985).
- S- matrix
. Solid material : structural stability resistance to erosion
. Pore space : porosity water + air
* microporosity WHC
* macroporosity -infiltration
* runoff
* percolation
- Pedologic features: soil genesis
3. Mesolevel:
At the level of horizon, formed by aggregates coming together. For horizon designation
and further explanation on the description of horizons we will use the FAO guidelines
(see describing soil profiles).
4. Macrolevel:
That is the level of pedon, the smallest soil unit that we study. The best references to refer
to are: Buol et al., 1980; USDA, 1975, and the pedosphere on line (Juma, 1999:
pedosphere on line).
5. Megalevel:
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That is the polypedon level, with the units of measurement of meter to kilometers. We
make use of Buol et al., 1980, and the pedoshere on line, for further explanation.
Normally, a soil is born with the formation of a A-horizon (that is an AC profile, one of
the members of the Entisols). Further development, leads to the formation of a B-horizon
(that is then an ABC profile, which may corrspond with the formation of a Cambic
diagnostic horizon, the simplest classification name may be one of the members of the
Inceptisols). Further development will lead to the formation of argillic (Bt), Spodic (Bsh),
Oxic horizons, etc, meaning Alfisols, Ultisols, Spodosols, Oxisols, respectively.
B. Soil properties (http://www.pedosphere.com; USDA Soil Survey
Manual; FAO Guidelines for Soil Profile Description; also under
http://nesoil.com/properties/index.htm and www.nrcs.usda.gov/programs
Physically, a mineral soil is a porous mixture of inorganic particles (fine and coarse
fractions), decaying organic matter, air, and water. The larger mineral fragments usually
are embedded in and coated over with colloidal and other materials. Organic matter acts
as a binding agent, taking care of aggregating. This complex is the source of many
physical characteristics, which may be explained in two sections, namely texture and
structure. Other related properties, such as consistency, porosity, bulk density,
permeability, infiltration, moisture content, and many others can be explained within the
frame of, and relating to, the above sections:
Texture: concerned with the size and the proportionality of mineral particles of various
sizes (sand, silt and clay) in a given soil. Many ( physical and/or physico- chemical) soil
properties and characteristics, such as water holding capacity, fertility, and workability
can be explained referring to the soil texture (also referred to as particle size distribution;
see the above mentioned sources ; among others “pedosphere” online).
Structure: concerned with a bonding together into aggregates of individual soil particles.
Individual soil aggregates (peds) are classified into several types (see pedosphere on
line). The role of structure is very vital in many soil-oriented issues, such as water
movement (infiltration, permeability, run- off) erosion, sedimentation, etc.
C. Describing soil profiles:
Soil survey is associated with a laborious fieldwork. Many soil observations (mini-pits,
pits and augerings) are made and studied. Soil profile description is explained in Soil
Survey Manual (USDA, 1990), but the pocket size guidelines we normally have with us
in the field is the one of FAO (1990).
The pit is first carefully studied for its different horizons and layers (H, A, E, B, C, R)
and then described horizon by horizon, for colour, texture, structure, etc.
The description card is filled out and kept in a file for later processing (the procedure will
be demonstrated in a field excursion)
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Texture: Soil texture is determined in the field, simply by making paste and testing it for
stickiness (presence of clay), grittiness (presence of sand), and being or not soapy
(presence of a certain amount of silt). Obviously, all soil samples contain sand, silt and
clay. The question to ask yourself in the field is whether the sample in your hand is loamy
sand; loam; clay loam; or clay. If the sample is sticky and that you can manipulate it to
form long ribbon (by rubbing between your fore-finger and thumb of, preferably, your
left hand, in order to have your right hand clean for writing, etc), it is clay. Ribbons are
also formed if the sample is clay loam, with the difference that here the ribbon is bending
down around your fore-finger. In addition the soil is not so sticky as in the case of clay.
With loam one cannot form ribbon. A very striking characteristic of loam is that the soil
paste feels very soft and smooth. Any of these textures (clay, clay loam, loam) can have
more than a given amount of sand (see the USDA Textural Triangle) in which case the
adjective “sandy” will be added to the name, that is, sandy clay, sandy clay loam, and
sandy loam, respectively. If there is too much sand in “loam” so far that no ball can be
formed, then we would have “loamy sand”. If one hesitates between the two (sandy loam
and loamy sand) make then a ball from the paste and throw it up for about 50cm and
catch it back in the hand. If soil sample stays as a ball it is sandy loam but if it collapses it
is “loamy sand”.
The texture classes loam, clay loam, and clay may be silty, that is, when silt percentage is
more that a certain amount (see the USDA Textural Triangle). Then we will have silt
loam, silty clay loam, and silty clay, respectively. In field, a few drops of water is added
to the soil sample and gently rubbed with the thumb in order to check whether the soil
feels soapy or not. If soapy, it is then silty.
The tests mentioned above are some general hints which help determining texture, but it
is very important to check these feelings with the laboratory, and/or with a senior soil
surveyor. This is specially important when you go to a new study area. Obviously, one
cannot expect that young soils, old soils, volcanic soils, soils with kaolinite clay type will
react similarly when manipulating for texture.
Structure:
When a soil (in the profile pit) does not show rock structure, we say there is soil
structure. One of the requirements of the Cambic horizon (a diagnostic horizon defined in
soil classification systems, USDA , FAO, or WRB) is to show more than 50% of soil
structure. A very weathered gneiss (saprolite) will still show bands of the weathered
felsic and mafic minerals, in which case decision should be taken whether rock structure
is more or less than 50%. Once we agree that we do not see rock structure we then have
to do with soil structure. Soils may be structured or without structure (structureless). The
term structureless is rather confusing. If there is no clear aggregate to recognize and the
soil material is coherent we speak of massive, but if non-coherent we speak of single
grained. These are considered soil structure, although we used the term “structureless”
(USAD Soil Survey Manual).
On the other hand, if aggregates have been formed they may be of plate-like, block-like,
and prism-like forms. Hereunder, we will have granular; crumb; fine through course,
weak to strongly developed subangular to angular blocky (subdivisions of the block-like);
fine through course, weak to strongly developed prismatic; or columnar, which occurs
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only in Natric horizons( both prismatic and columnar are different types of the prismlike); and thin through thick, fine through course platy structure type.
As you probably noticed, structure is described according to its form, size and the degree
of development. There is not any difficulty to learn about the form and the size, but to
determine the degree of development one needs to see how a senior soil surveyor is
doing. Use the hand-grip of you knife to gently hit a clod of soil that you hold in the hand
and watch how the clod breaks into smaller pieces (aggregates). The easier the clod
breaks into smaller peds the better the structure is. The clod breaks along the developed
planes of weakness (between structural elements). A strongly developed structure won’t
leave behind any wastes, that is, all broken pieces will be smaller structural elements. In
massive soils, no planes of weakness are developed. Breaking of the clod, in this case,
would only be possible by force.
D. Soil Classification:
As in many other disciplines, in soil science too, classifiaction is to help communication.
Similar soils are tried to put in given groups so that their correlation (of soils occurring in
the different parts of the world) become possible. Among the many classification
systems, the USDA Soil Taxonomy (USDA, 1975 and the later issues) is considered as
the most comprehensive, although many scientists look for an easier and more simple
system. The FAO-Unesco (in the 1970s) system and the more developed version of it, the
World Soil Reference Base (FAO-ISRIC reports 66 rev. 1, 1993 and 84 in 1998) are
some attempts to present a more simple soil classification. Personally, I am inclined to
work with a real organized and comprehensive system of soil classification, through
which well qualified useful interpretations can be done. I strongly believe that not all
users of soil maps are not supposed with the sophisticated classification anmes. There, we
have soil scientists for!!
In the USDA Soil Taxonomy, several categorical levels, such as ‘orders’, ‘suborders’,
‘great groups’, ‘subgroup’, ‘family’, and phases of family take care of the classification.
Example: All soils belonging to Alfisols (order name) will end with ‘alf’. Alfisols are
defined, using several criteria, for instance, having an argillic horizon, characterized by a
base saturation (BS%), at the depth of almost 2m from soil surface, of 35%, etc.
Xeralfs (suborder name) are those alfisols which, in first place, occur in the areas with
Xeric moisture regime (e.g., in a country like a great part of Spain, or Portugal, with
mediterranean type of climate).
Palexeralfs (a ‘great group’ name) are the Xeralfs with a thick argillic horizon, sign of
development and age.
Calcic Palexeralfs (a subgroup name) are those palexeralfs which also have a calcic
horizon.
After subgroup, appears the family name, which is formulated on the basis of family
differentiae, such as particle size class, mineralogy class, soil temperature classes, etc. An
example to be given here is: Clayey skeletal, illitic, hyperthermic.
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We recommend to continue the classification, at least in surveys at semi-detailed level, to
the phase of family, that is, to use terms such as very gravelly topsoil, strongly sloping,
etc (see Soil Survey Manual; USDA, 1990).
Soil resource inventory or simply soil survey
1. Introduction:
As already mentioned, soil is a complex 3-D object, the X and Y dimensions (its surface)
of which can be observed, if not covered by vegetation and/or other objects, whereas the
Z dimension (its depth) is not visible, hence quite difficult to describe and/or map it, in
order to know its distribution, which is often required for (land use) planning and other
purposes.
Soil survey is a complex operation, including a number of tasks in categorical levels
(Zinck, 1988). The strict domain of soil survey includes the phase of basic soil data
collection, synthesis of soil information, characterization of soils and environment, and
the multiple purpose soil interpretation. Zinck (1988) also considers two more levels,
where soil survey is employed in planning, at regional and local levels.
An obvious question in soil survey is how to map an object which owes its extent to the
variations of its forming factors in space and time, as the soil is the product of the actions
of climate, biota, and topography (relief) on rocks/ sediments in spans of time? What tool
should we use to extract information about the 3rd dimension, the depth? After rather a
long time of trying various ways such as grid survey, overlaying (synthetic approach),
etc. geomorphology proved to be the best tool.
2. Importance of geomorphology for soil survey
In order to discuss the importance of geomorphology for soil survey, it is sufficient to
check whether we agree with the following statements:
- Pedology and geomorphology are two of the fundamental disciplines within the
landscape ecology (IALE concept= http://www.Crle.uoguelph.ca.iale).
- Pedons and geoforms are the study objects of these disciplines, respectively.
- Both pedons (USDA, 1975) and geoforms (Zinck, 1988) are natural bodies,
occurring between lithosphere and atmosphere, including the biosphere, mainly
above the lithosphere.
-
Both geoforms and soils share the same forming factors, originated from
endogeneous or internal (material and energy) and exogeneous or external (
through climate, biosphere, erosion and sedimentation) sources:
Internal geodynamics (energy), through faulting, folding (in general, tectonics)
and volcanism govern the formation of material on which geoforms are formed.
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In its turn, the material, depending on its lithology (texture, structure,
mineralogy), tectonic layout, and age, controls the formation of the geoforms.
On the other hand, external sources, through climate, biosphere, erosion,
sedimentation, largely contribute to the formation, transformation and/or
destruction of the geoforms and soils.
-
Geomorphology contributes to two activities within the complex process of soil
survey, namely to 1. soil mapping, and 2. soil formation
In soil mapping, two questions are to be answered, namely:
1- who they are? meaning that their address (site selection) should be
known, their characteristics, and the category where they fall under (soil
classification), and
2- where they are? meaning that their distribution and extension should be
known.
On top of all what is said above, geomorphologic processes and environment are
used as factors and framework of soil formation and evolution:
1- geomorpic process associated with lateral movement is not useful only on
sloping areas where catena formation, truncated/buried sequence are resulted,
but also on flat areas, for instance, in the case of levee-basin sequence, in
fluvial landscapes,
2- geomorphic process also indicates the time factor (morpho-chronology),
through which the degree of soil development is estimated.
In summary, incorporating geomorphology in various steps of the soil survey operation
adds useful information.
3. Iimplementing geomorphology in soil survey
Different ways of using geomorphology for soil survey have been tried out, a few
examples of which can be given here (Zinck, 1988):
- Terrain analysis (ITC approach explained in van Zuidam, 1985)
- Physiographic approach of CIAF-ITC (in Colombia), and of CSIRO (Autralia)
- Landtype approach (ITC Soil Division approach, which started under Buringh,
further developed under Vink, Bennema and Goosen)
- SOTER legend (FAO, 1993): developed at ISRIC, Wageningen, The Netherlands
(in the time of W. Sombroek, as the director). This is an universal legend for a
world soils and terrain digital database, to be used at scale 1000.000.
These and many other approaches (explained in Zinck, 1988) aim mainly at the
establishment of mapping legends adapted to local or regional conditions.
In general, a solid structure is lacking. This holds true even in those of the approaches
which are called to be categorical. The lack of structure is sometimes so large that
‘mountain’ and ‘basin’ are put in one and the same categorical level. Obviously, all
authors have tried to follow a sort of structure, but it does not seem that they were
successful. The problem is that geomorphology is quite a controversial subject and that a
real taxonomic classification is lacking, whereas some other disciplines such as botany
and soils have succeeded to establish one.
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4. Structure of a taxonomic system
Geomorphologists have always been concerned by classification. In a few examples
given (Zinck, 1988), one can see that different authors have used different criteria, which
have been changing over time.
Examples of geomorphic classification:
a. Tricart-Cailleux , the authors of ‘morphometric classification’ used
size and structural geomorphology to classify geoforms,
b. In genetic classification, the authors used structural geomorphology
(types of relief such as cuesta, folded relief), climatic geomorphology
(types of molding such as glacial molding, aeolian molding), and
azonal geomorphology (alluvial forms, lacustrine forms, coastal
forms),
c. In genetic-choronologic classification, on the basis of a subdivision of
the earth’s surface into broad climatic zones, a set of morpho-climatic
domains and associated geoforms was resulted and used to do the
classification.
Considering that our knowledge on how to establish a taxonomic system has considerably
improved (USDA, 1975), the above classification systems look far from satisfactory. By
now, we have learnt that:
-dimension can not be considered as a diagnostic criterion,
-geographical distribution of geoforms should not be taken as a criterion,
-choronology of geoforms should be included in the legend, not as a criterion,
-the genesis of geoforms should be taken only at lower levels of the system, that is to say
that a taxonomic system starts with simple criteria and ending with more complicated
ones. The criteria, for which much data are needed might be used but only at lower
categories.
Obviously, lack of clear definitions and the conflicting views amongst the
geomorphologists, regarding terminology, genesis, and so on are a few of the limitations
to name here. The objective of a taxonomic system in geomorphology would be to
taxonomically classify the geomorphic unit, that is, the geoforms. Such a system should
aim at classifying geoforms by the characteristics and not by forming factors.
To establish a taxonomic system, 5 main steps will have to be followed:
1. selection of the most appropriate system structure. A selection can be made out of
a)hierarchical; b) relational; c) network; and d) lineal system structure. In the
system of Zinck (1988), following the USDA Soil Taxonomy (1975), hierarchical
structure is considered as the most appropriate one for the multi-categorical
system, as the geoform is.
2. Definition and number of categories (these are further subdivisions of the system).
A category is a level of abstration. Each category may have one or more class(es).
Further, come the taxa. Each taxon is a member of an established class.
3. Definition and number of classes
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4. selection and hierarchization of attributes (these are characteristics used for
defining limits of classes)
5. Nomenclature for naming categories and classes
Example -- Principles and mechanism of classification:
Figure 1: showing the population of objects, in two different colours and 2 sizes
Table 1: showing 3 critera and a few varieties of each one
Attributes
Attributes states
Colour
Red
Green
Size
Large
Small
Form
Square
Triangle
Circle
Square
Yel.
Small
Triangle
Circle
Large
Green
Small
Figure 2: showing one way of classifying the objects. You will realize that
there six possibilities
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Examples from the USDA Soil Taxonomy:
At order level:
Ultisols
|
0
Alfisols
35%
100% BS
At suborder level:
Dystropepts
0
|
Eutropepets
50
100% BS
Examples of categories in the USDA Soil Taxonomy:
•
•
•
•
•
Order (e.g., Inceptisols, Alfisols, Ultisols)
Suborder (e.g., Eutropepts, Dystropepts)
Great group
Subgroup
Family
A few questions/remarks: will you answer the first question (write your answers down):
Ouestion 1:
At what level (in a multi-categorical classification system, like the one of the above
exampl) would you think the following geomorphic forms should be placed?
- Mountain;
- Hill;
- Alluvial fan;
- Levee;
- Summit
Question 2:
What do we see from ?: (answers are given in between the brackets)
Satellite? (Large portion of a continent),
Airplane? (Mountain range)
Helicopter? (Structural/ erosional environment)
Car? (Terrace)
While walking ? (Levee/ basin)
Question 3:
What do you think about the following geomorphic terms to use to answer the above
questions (of question 2):
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Satellite? Geostructure
Airplane? Morphogenetic environment
Helicopter? Landscape
Car? Relief-type
While walking? Landform
5. The proposed system by Zinck (1988)
Six categorical levels are considered as follows:
6- geostructure (order)
5- morphogenetic environment (suborder)
4- landscape (group)
3- relief/molding (subgroup)
2- lithology/facies (family)
1- landform (subfamily)
Geostructure:
Definition:
Large continental portion characterized by a specific geological structure
Taxa:
- Cordillera: system of young mountain ranges
- Shield: relatively stable continental block
- Geosyncline: large sedimentary basin
Morphogenetic environment:
Definition:
Broad type of biophysical medium
Taxa (on the basis of various environments):
- Structural : controlled by internal geodynamics;
- Depositional (carried by water, ice, wind) ;
- Erosional (denudatioanl);
- Dissolutional (e.g., karst); - Residual(e.g., inselberg)
- Mixed (e.g., structural dissected by erosion)
Landscape:
Definition:
Large portion of land characterized either by a repetition of similar relief-types or an
association of dissimilar types.
Taxa:
Valley; Plain; Peneplain; Plateau; Piedmont; Hilland and Mountain.
Be aware that in some cases the concept of landscape is quite ambiguous, for instance,
when we talk about valley!!
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Relief-type/molding:
Definition:
Relief-type: geoform determined by a given combination of topography and geological
structure (e.g., cuesta relief-type),
Molding: geoform determined by specific morphoclimatic conditions or morphogenetic
processes (e.g., glacis, fan, terrace, delta)
Taxa:
Structural
Depression
Mesa
Cuesta
Creston
Hogback
Bar
Flatiron
Escarpment
Graben
Horst
Anticline
Etc.
Erosional
Depression
Vale
Canyon
Glacis
Mesa
Hill
Crest
Etc.
Depositional
Depression
Swale
Floodplain
Flat
Terrace
Mesa
Etc.
Dissolutional
Depression
Dome
Tower
Hill
Polje
Canyon
Dry vale
Etc.
Residual
Planation
surface
Dome
Inselberg
Tors
Etc.
Lithology (See also Farshad, 2005. A Syllabus on “Introduction to applied
geomorphology for soil scientistd (geopedologists):
Definition:
Lithology refers to the petrographic nature of the hard rock and the facies of the soft
cover formations.
Taxa:
-Rock classes
-Material facies, such as glacial, periglacial, alluvial, colluvial, litoral or coastal, mass
movement, volcanic, mixed, anthropic, etc.
Landform:
Definition:
Landform is considered here as the generic concept for the lowest level of the proposed
hierarchical system.
Landform=topographic form+geomorphic position+geoch-ronologic unit= soil formation
frame.
Taxa:
See next chapter (e.g., summit, shoulder, overflow basin)
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Attributes for determining geomorphic taxa:
Attributes are characteristics used for description, identification and classification of
geoforms. To establish a system we will have to decide on:
- what attributes to be used for describing and identifying geoforms? and
- what attributes for each categorical level?
Classes of attributes
1- Morphographic: for describing the geometry of geoforms
2- Morphometric : for measuring the geoforms (DEM is useful)
3- Morphogenetic: for determining the origin and evolution of geoforms
4- Morphochronologic: circumscribing time context
1. Morphographic attributes
a. Topography (transverse section of a portion of land):
*Shape (e.g., flat, undulating, rolling, hilly, steeply dissected,
mountainous)
*Form (e.g., level, concave, convex,irregular)
*Exposure (e.g., S., N.)
b. Planimetry (vertical projection of geoform boundaries on a
horizontal plane)
*Configuration (e.g., elongated, narrow, rounded)
*Contour design (e.g., arched, lobulate, irregular)
*Drainage pattern(dendritic, annular, radial)
*Surrounding conditions (e.g., overtopped by…..)
*Bordering unit (e.g., plain overtopped by a plateau)
2. Morphometric attributes
Morphometry refers to quantitative features of geoforms:
a. relative altitude (e.g., high, medium, low)
b. valley density (drainage density)
c. slope gradient (in %)
These are no-diagnostic attributes, which can be used at any categorical level with
variable weight. DEM is an useful instrument.
3. Morphogenetic attributes
a. Particle size distribution; very important attribute, because it:
*allows inference of other material properties (e.g., bulk density)
*reflects geo- and pedodynamic features
b. structure (geogenetic structure, pedogenetic structure)
c. consistence (mechanical behaviour)
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d. mineralogy (origin of depositional material, morphoclimatic conditions, catena model,
morphoscopy)
4. Morphochronologic attributes
Properties used to study the history of geoforms:
a. Degree of activity (sand dunes, solifluction, coastal bar)
b. Age of geoforms:
*absolute dating (e.g., radiometric techniques)
*relative dating
c. quaternary geology; use of reference systems (e.g., European and
American glaciation-dating: Riss, Illinois, etc)
d. pedostratigraphy: where soil properties (e.g., colour, pH, CEC, leaching
indices) are used to estimate the relative age.
Differential importance of the attributes; weight and level:
Concerning the importance of the attributes for classifying geoforms, 3 classes are
distinguished:
1. differentiating attributes: A slope facet must be concave to be classified as
footslope. The topographic profile (concavity) is a differentiating attribute,
2. Accessory attributes reinforce the differentiating ones, such as the occurrence of
depositional lens in footslope deposites,
3. Accidental attributes are used to create phases of taxonomic units, such as height
and slope.
At the same time, there are a few rules applied to the use of the attributes in the different
levels in such a hierarchical system:
- Less attributes are needed at higher levels,
- Attributes at higher levels are descriptive,
- Attributes at higher levels have an aggregating function
- Implementation of attributes at higher levels is by means of API or visual
interpretation of satellite image, whereas at the lower levels field and laboratory
data are needed
Geoforms systematics (see also Farshad, 2005b)
A. Geoforms mainly controlled by geological structure:
1. Structural geoforms
2. Volcanic geoforms
Relief types
Landform types
Depression
Crater
Caldera
Maar
Lake
Ash Cone
Slope facet complex
Cinder Cone
Crater
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Spatter Cone
Shield Volcano (Hawaian)
Strato Volcano
Cumulo Volcano
Flat
Mesa
Cuesta
Hogback
Bar
Dyke
Escarpment
Flanks
Lava flow
Block (aa) lava
Ropy (Pahoehoe) lava
Fluvio-volcanic flow (Lahar)
Cinder field
Ash mantle
Planeze
Hanging lava flow
Sill
Longitudinal dyke
Annular dyke (ring dyke)
Volcano scarp
Neck
Volcanic plug
3. Karstic geoforms
B. Geoforms mainly controlled by morphogenetic agants: The six main
families of landforms falling under this group are:
1. Nival, glacial and preglacial; 2. Eolian; 3. Alluvial and colluvial
Erosional:
Depositional:
Ablation surface
Load excess facies:
Rill
Point bar complex
Gully
River levee
Gully complex (badlands)
Distributary levee
Deltaic levee
Splay axis
Splay mantle
Crevasse splay
Splay fan
Splay glacis
Overflow facies:
Overflow mantle
Overflow basin
Decantation facies:
Decantation basin
Backswamp
Ox-bow lake
Infilled channel
Colluvial facies:
Colluvial fan
Colluvial glacis
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2. Lacustrine
3. Gravity and mass movement
4. Coastal
C. Banal geoforms (dissected hills and ridges)
D. Fluvial landforms and depositional systems
Application of soils to physical and environmental studies
Birkeland (1999) in his book titled “Soils nd Geomorphology” has a chapter on
application of soils to geomorphological, sedimentalogical, and environmental studies,
where he refers to many case studies where soils have been, as a basic science, applied to
other disciplines. Examples are; use of soils in Quternary stratigraphic studies, using soils
to date tectonic activity (e.g., dating faults and folds), using soils in archaeological
studies, using soils in environmental studies, etc.
This chapter of the above book supports the statement that soil is the history book of
landscape, on the basis of which I have published a few papers. The two enclosed papers
show examples of the use of soil in other disciplines:
How far are we with digital soil mapping
A digital terrain model is a mathematical (or digital) model of the terrain surface (Li et al,
2005). The mathematics takes care of the interpolation process, which has been advanced
with increasingly efficient and cheap computation power and storage, availability of
digital contour, stream, and orthophotographic data (http:\\
www.ffp.csiro.au/nfm/mdp/softdem.htm). Li et al. (2005) classify the surface modeling
approaches as: 1. point-based modeling, 2. triangle-based modeling, 3. grid-based
modeling and 4. a hybrid approach combining any of two of the three approaches. The
required data for the digital terrain modeling may come either from field survey (eg., use
of conventional surveying instrument or GPS), from stereo pairs of aerial (or space)
images using photogrammetric techniques, or from digitization of the existing
topographic maps. The latter source is the most commonly used technique, although more
and more people make use of the freely available DEM’s, downable from SRTM (Shuttle
Radar Topography Mission) at http://srtm.usgs.gov/. However, this product won’t satisfy
those who need high resolution data (Farshad et al., 2005).
Almost all well known commercial GIS packages are equipped with a submodule taking
care of generating DTM. ARCINFO, for instance, is equipped with ANUDEM, a
program developed in the Centre of Resource and Environmental Sciences of the
Australian National University in Canberra, which supports production of grid-based
DEMs using contourline map. Or in ENVI software, the submodule “topography”
supports generating DTM using ASTER images. GRASS GIS software is also equipped
with a number of terrain analysis procedures, especially for hydrological modeling and
erosion mapping. There are also a few freely available packages, such as TARDEM and
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22
TauDEM developed at the Utah Water Research Laboratory
http://www.itc.nl/personal/shrestha/DTA/DTA_in_ILWIS.pdf.
The process of inventory/ mapping includes collecting data (usually from points) and
storing them with their geographic (spatial) properties, which can be used to track down
distribution (map presentation). The advances in the world of remote sensing are
considerable. Combined use of both remote sensing and GPS enormously facilitate the
process of data collection/ fieldwork. However, remotely sensed data, whatsoever the
sensor, usually depict the land surface. This means that much information can be
extracted from the remotely sensed data if flora, and to a certain extent, fauna are the
study subject. In the same way, the advancement in the domain of data base management
system (DBMS), both spatial and non-spatial, in a GIS environment is striking. Data are
easily stored and are retrievable in point, vector and/or raster, when required. Comparing
these, which have been developed in the last couple of decades, with the ink-on-paper
approach shows the extent of advancement.
The once well formulated set of soil survey procedures, which, to many people, looked as
if soil survey was a routine activity, is agitated. The newly developed technology in the
field of data acquisition and management is taking over the once known conventional
approaches, though still in a shaky conditions. The tendency is to go digital,
quantification should overcome qualification.
While still soil surveys are being carried out, though not as often as it used to be, several
questions are asked by many people involved, simply because soil survey has become too
expensive. Some of the questions are: What about the soil surveyors who have been
trained to document their mental models in maps and reports. Didn’t this group do a good
job? And was the soil map a good communication tool (Hudson, 1992)? Should this
group continue what they did for decades?
On the other hand, we should confess that it is a fact that soil mapping has benefited from
the newly developed technology in the fields of exert system, decision support system,
etc (Hengl et al, 2002, Bui and Moran, 2001 and 2003; Moran and Bui, 2002; Bui, 2004).
However, the field has not sufficiently used the advances in remote sensing and
mathematical modeling. The latter tools have been used, often at research level.
References:
Birkland, P.W. 1990. Soils and geomorphology (3rd edition). Oxford University Press, Inc., New
York (http://www.oup-usa.org.).
Brewer, R. 1964. Fabric and mineral analysis of soils. John Willey& Sons, New York, 407p.
Bullock, P., Federoff, N, Jongerius, A., Stoops, G., and U. Babel. 1985. handbook for soil thin
section description. Waine Research Publ., Wolver Hampton, England, 152p.
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23
Bui, E.N. 2004. Soil survey as a knowledge system. Geoderma 120. p 17-26. Available
online at www.sciencedirect.com.
Bui, E.N. and C. J. Moran. 2001. Disaggregation of polygons of surficial geology and
soil maps using spatial modeling and legacy data. Geoderma 103, 79-94.
www.elsevier.com/locate/geoderma.
Bui, E.N. and C. J. Moran. 2003. A strategy to fill gaps in soil survey over large spatial
extents: an example from the Murray-Darling basin of Australia. Geoderma 111, 21-44.
Available on line at www. sciencedirect.com.
Buol, S.W., Hole, F.D. and R.J. Mc Cracken. 1980. Soil genesis and classification. Iowa State
University Press, Ames, 404p.
FAO, 1990. Guidelines for soil profile description. FAO, Rome, Italy
FAO-ISRIC, 1993. Global and National Soils and Terrain Digital Databases (SOTER). World
Soil Resources Report No. 74. FAO, Rome, Italy. 122p.
FAO. 1998. World Reference Base for Soil Resources, Reports, FAO, Rome, Italy.
Farshad, A., Udomsri, S., Yadav, R.D., Shrestha, D. P. and S. Sukchan. 2005a. Understanding
geopedologic setting is a clue for improving the management of salt-affected soils in Non Suang
district, Nakhon Ratchasima, Thailand. Presented in HinHua, Thailand, in wrap up seminar of the
LDD-ITC funded research project.
Farshad, A. 2005. An introduction to applied geomorphology for soil scientists (geopedologists).
Lecturenotes (unpublished), ESA, ITC, Enschede, The Netherlands.
Farshad, A., Shrestha, D.P., Munchun, R. and A. Suchinai. 2005b. An Attempt to Apply Digital
Terrain Modeling to Soil Mapping, with special attention to sloping areas; Advances and
Limitations. Presented in HinHua, Thailand, in wrap up seminar of the LDD-ITC funded research
project.
Farshad, A., Udomsri, S., Hansakdi, E. and D.P. Shrestha. 2006. GIS-based geopedology, a way
to predictive soil mapping. IUSS, Philadelphia, Pennsylvania, USA.
Gerrard, A.J., 1981. Soils and landforms, an integration of geomorphology and pedology. George
Allen and Unwin, London, 219p.
Goosen, D. 1967. Aerial photo-interpretation in soil survey. FAO Soils Bult. No. 6, FAO, Rome,
55p. ; and also ITC, Enschede, The Netherlands.
Hengl, T., Rossiter, D.G., and S. Husnjak. 2002. mapping soil properties from an existing
national soil data set using freely available ancillary data. 17th WCSS, BKK, Thailand.
Paper No. 1140.
Hudson, B.D. 1992. The soil survey as a paradigm-based science. Soil Science Society of
America Journal 56, 836- 841.
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24
Huggett, Richard John. 199. Geoecology, An evolutionary approach. Routledge. London and
New York.
Jenny, H. 1941. Factors of soil formation. McGraw-Hill, New York, 281p.
Jenny, H., 1980. The soil resource. Origin and behaviour. Ecological stidies, v. 37. SpringerVerlag, New York, 377p.
Juma, N. 1999. The pedosphere and its dynamics. A system approach to soil science. Salmon
Productions, Canada.(http://www. Pedosphere.com)
Li, Zhilin, Qing Zhu, and Christopher Gold. 2005. Digital terrain modeling: principles
and methodology. CRC Press. Boca Raton, London, New York, Washington DC.
Moran, C.J. and E.N. Bui. 2002. Spatial data mining for enhanced soil map modeling. Int.
J. Geographical Information Ecience. Vol. 16, No. 6, p. 533-549.
McBratney, A.B., Mendonca Santos, M.L. and B. Minasny. 2003. On digital soil mapping.
Geoderma 117, 3-52. Available on line. Available on www.sciencedirect.com
USDA, 1975. Soil Taxonomy. Handbook No. 436, 754p.
USDA, 1993. Soil Survey Manual. Handbook No. 18, 437p.
Zinck, J.A. 1988/89. Physiography and soils; soil survey courses; subject matter K6 (SOL41,
lecture-notes), ITC, Enschede, The Netherlands.
Zonneveld, I.S. 1979. Land evaluation and Land(scape) science. ITC, Enschede, The
Netherlands, 134p.
Zuidam, R.A. van. 1985. Aerial photo-interpretation in terrain analysis and geomorphological
mapping. ITC, Enschede, The Netherlands.
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