Conceptualizing Geomorphology
David Munasirei (2014)
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Definitions:
Derivation of the term: geo = earth; morph = form; -ology = study of
“the morphology [the science of form] of landforms including those under the sea “
The Chambers Concise Dictionary (1984:403)
- The scientific study of the origin of landforms based on cause-and-effect
relationship (Whittow, 1970). It comprises of two approaches: the earlier inductive
approach and the deductive approach which depends largely on measurements of
currently operating geomorphic processes.
- Geomorphology is a science that analyzes and describes the origin, evolution,
form, and spatial distribution of landforms.
Sources of Information and Methods of Analysis (Chorley, 1966 ; Chorley et al., 1984)
Availability of a battery of techniques & instruments to monitor geomorphic processes
e.g. movement of debris on slope, transport of sediments in rivers,.
Sources of Information and Methods
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Sources & analysis generate data on short-term landform change
Fieldwork observations: daily, monthly yearly e.g. slope evolution in clay
badlands by Schumm; use of remote sensing techniques in collecting & monitoring
processes; use of topographic maps
Space-time simulation in landform analysis: e.g. Darwin – corral reef formation
& Davis ‘cycle of erosion’ assumptions used not rigorous enough; use of ergodic
hypothesis (has a very specific meaning in probability theory). A system that
eventually returns to its original condition - even if that is a long time - so that,
roughly speaking, averages over time will suffice to explain the system.. E.g. As used
in geomorphology, suggests that under certain circumstances sampling in space can be
equivalent to sampling through time. Geomorphologists have sometimes sought an
understanding of landform evolution by placing such forms as regional valley-side slope
profiles and drainage networks in assumed time sequences. The concept of the cycle of
erosion was based to a large extent on ergodic assumptions, as was Darwin's model of coral
reef development
Sources of Information and Methods
- Laboratory observations in hardware models
- Simulation: use of simulation models
a) Hardware models – laboratory flumes used to study specific geomorphic
processes e.g. transport of sediment by water &wind; effects of lowering the base
level. Challenge of replicating scale.
b) Analogue models – e.g. replacement of materials in real world with other
materials which enable the effects of processes to be more readily observed like
use of cly to synthesize effects of glacier flow
c) Mathematical models (replaced some analogue models)
i)
Deterministic mathematical models: based on exact relationship between
independent (causal) variables and dependent (responsive) variables e.g.
prediction of slope profile transformation over time from some initial form.
ii. Stochastic Mathematical models: incorporate
- Analysis of deposits (sedimentology)
- Office observations
Geomorphic System
Exogenic: at or near earth’s surface
Endogenic: energy initiating the action is inside the earth
• See handout
Relationship Related Disciplines
Based on M.A. Summerfield (1991)
Discipline
Contribution to
Geomorphology
Contribution from
Geomorphology
Biology
Role of vegetation cover in
affecting rates of erosion
Topographic control over
micro-environments of plant
growth
Climatology
Effect of climatic elements on
rates and nature of
geomorphic processes
Effect of surface deposits and
morphology on climatic
variables
Engineering
Techniques for analysis for
slope instability
Identification of morphological
features indicative of slope
instability
Geology
The form and origin of
mountain systems
Perspectives in understanding
the spatial distribution and
origin of mountain systems
Sedimentology
Study depositional processes of
sediments
Reconstruction of past erosional events
from sedimentary sequence
Form of alluvial channels in
interpretation of fluvial sediments
Geomorphology and Disciplines (cont.)
Geophysics
Mechanisms and rates of uplift
Theory of plate tectonics
The clastic and plastic
deformation of rocks under
pressure and thermal
conductivity (their primary
intention is not of describing
and analyzing landforms)
Erosional response of land
surface uplift (e.g.
morphological evolutionary
models)
Describing and analyzing
global morphology
Describing and explaining the
clastic and plastic deformation
of rocks in origin and
development of landforms
Hydrology
Study the flowing of water
(surface and subsurface)
Frequency and intensity of
flooding
Influence of surface and
subsurface flow on landforms
Influence of flow on sediment
concentration
Space Sciences
Context for understanding special
characteristics of landformcreating environment on the Earth
Interpretation of planetary
landscapes by analogy with
terrestrial landforms
Geomorphology and Disciplines (cont.)
Pedology
Soil genesis
Soil classification
Soil morphology
Soil survey
Soil characterization and
analysis
Topographic control over soil
forming processes (external
and internal soil building
processes)
Spatial distribution of soils
Land capability classification
for land use
Seismology
Concerned with the causes
and prediction of earthquakes
Spatial distribution of
earthquakes and their
influence on landforms
Mineralogy (Geochemistry)
Concerned with rate and
nature of chemical reactions of
minerals and rocks thereby
providing data for weathering
processes
Spatial distribution of nature
and rates of chemical
weathering in morphogenetic
regions
Mobilization of elements in
earth surface environments
Approaches to Geomorphology (Chorley et al., 1984: 4)
1. Conceptual Approaches
- Historical Approach: “studies which attempt to deduce from
erosional and depositional features of the landscape evidence
relating to the sequence of historical events (e.g. tectonic, eustatic,
climatic etc.) through which it has passed.”
- Functional Approach: “studies of reasonably contemporary
processes and behaviour of Earth materials which can be directly
observed and which help the geomorphologist to understand the
maintenance and change of landforms.”
2. Systems Approach
3. Temporal and Spatial Scales
Systems Approach
Hierarchy of Spatial and Temporal Scales in
Geomorphology
Dimension
Examples of Landforms
spatial
scale
Linear
km
Endogenic
Micro
<0,5
Meso
0.5 – 10
Macro
10-103
102 - 106
Block faulted
terrain
Cyclic time
(107a)
Mega
10-103
102 - 106
Major Mt
ranges
Cyclic time
(107a)
Spatial
km2
<0.25
0.25-102
Temporal Scale
Exogenic
Fluvial
Aeolian
Minor fault scar
Steady time
(101a)
Small Volcanoes
Dynamic time
(103a)
Activity of Systems Approach
System
Morphological
Cascading
Processresponse
Control
SubDiscipline
Independent
Variable
Dependent
Variable
Example
Evolutionary vs. Functional
Evolutionary
Functional
Reasoning
Inductively designed
deductively used.
descriptive/qualitative
approach
Inductively designed,
deductively used. Quantitative
in approach
Temporal scale
Cyclic e.g. Davis, Penck,
Contemporary processesKing, Budel. Cyclic time (106 equilibrium e.g. Gilbert, Hack.
years)
Steady time (one day); Graded
time (100-100 years); Dynamic
time (one million years) i.e.
different states of equilibrium.
Spatial scale
Large-scale
Small scale
Explanation:
predominant
mechanisms
Denudation chronology
Positive feedback
Long relaxation time
Adjustments to
internal/external factors
Negative feedback
Short relaxation time
Functional Approach (advantages)
Advantages
• avoids the need to extrapolate from evidence to untestable inferences
about landscape history;
• provides opportunities for measurement and experiment leading to
quantifiable relationships between landscape processes and forms;
• permits greater specialisation
Disadvantage
• difficulty of generating an understanding of long-term landscape
evolution
Activity: With examples compare and contrast evolutionary and functional
approaches.
Landforms and Landscapes
• Subject matter: Surface materials: Surface processes and
Surface features
• Scientific study of landforms and landscapes (IMAGES)
• Types of landforms: boulders, hills, valleys, floodplains, sinkholes,
moraines, etc.
• Types of landscapes: Aeolian, , Fluvial, Glacial, Karst
Identify this landform
Identify this Landform
Activity
a) Identify the landforms above
b) Were the processes that created the relict landforms:
destructional or constructional?
c) Are the modern processes modifying this landform:
destructional or constructional?
d) With at least FOUR case studies discuss the contribution of
geomorphology to and from other disciplines
What are some of the unique erosional and depositional features you
find in a limestone cavern?
Landscapes: Type of Desert?
- Desert
De
se
rt
Type of Landscape?
Activity
• For the Two landscape images above:
a) Identify the landscape (Aeolian or Fluvial or Glacial or Karst?) [Be
specific in identification)
b) Were the processes that created the landscape: destructional or
constructional?
C) Are the modern processes modifying this landscape:
destructional or constructional?
Themes: Basis of Low & High Order Questions
• Study of landforms and landscapes (the “what”)
• Study of landforms and landscapes – spatial distribution (the
“where”) – hence the spatial perspective.
• Occurrence of events over time (the when hence temporal
perspective
• Study of surface processes responsible for landforms / landscapes
(the “why”).
• Relationship between landform scale and age (the “how”).
• Landforms can be explained in terms of structure, process and
time (the “why”)
• Applied geomorphology – (why and how)
Sub-disciplines of Geomorphology: Define
• Denudation Chronology
• Climatic Geomorphology: Climatic Morphogenesis (morphoclimatic
regions)
• Structural Geomorphology
• Quantitative Geomorphology; Dynamic Geomorphology and
Explanatory Geomorphology
• Morphometry/Statistical or Quantitativ Geomorphology
• Dynamic Geomorphology
• Anthropogeomorphology
The Systems Approach in Geomorphology
Determinism cont.
DE cont..
Comparison of Shallow and Deep Ecology