Earth Science Lecture Notes – Unit 1
SECTION 1.2 LANDSCAPES AND GEOMORPHOLOGY
Introduction to Geomorphology
What is geomorphology?
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Definition: The study of the landscape: Geomorphology entails the systematic
description of landforms, the analysis of the processes that form them, as well as
understanding the function landforms and their response to changes in energy (Geo, G.
the Earth; Morph, G. Form, ology G. the science of)
o Landscape: Mountainous Terrain--the combined effect of numerous landforms
o Landform: An individual feature--a slope, valley or mountain
Geomorphology draws upon all fields of geology, such as: structural geology,
geophysics, mineralogy, petrology, sedimentation and stratigraphy, hydrology, glacial
geology, paleoclimatology, etc.
What produces a landscape?
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A landscape is the product of the interaction between the follow factors through time:
o Energy: Driving forces behind geomorphic change; drives the hydrologic cycle,
chemical reactions on the earth's surface, uplift, subsidence, etc.
 Solar energy:
 -2 cal/cm2-min reaches the outer atmosphere.
 -30 to 14 % is absorbed into the system--depending on latitude
 Geothermal energy
 -derived from decay of radioactive elements and residual heat
 -gradient ± 20-30°C/km (crust)
 Gravity
 g= acceleration due to gravity=GM/r2 =980 cm/sec2 or 980 gals
 G=gravitational constant=6.67x10-11 N-m2/Kg2
o Resisting framework: lithology and structure
o Structure: Defines the grain of the topography (joints, fold patterns, layering,
arrangement of rocks of varying resistance)
o Process: The manner in which the ambient forces are applied to cause change.
Processes (endogenic and exogenic) are understood by applying the Law of
Uniformitarianism
 endogenic: Volcanism and Diastrophism: tectonics, orogenesis and
epierogenisis
 Examples:
 Tectonics processes: Plate tectonics (e.g. orogenic
processes and rifting)
 Volcanism: Intraplate hotspot activity (lava plateaus and
volcanoes) arc volcanism, sea-floor spreading
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Epierogenic processes: regional uplift and subsidence
caused by mantle anomalies, glacioisostacy, etc.
The role of isostacy
exogenic:
 Examples:
 weathering and erosion
 Hydrologic cycle and related fluvial processes
 glaciation
 eolian
 biological activity and man (?)
c. extragenic (my term)--meteor impact
 Importance:
 water (?) from comets?
 mass extinctions
 craters and large impact structures
Important considerations
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Scale of the system: Relationship between size and duration
Geologic history (relaxation time of past events)
Magnitude and frequency of events affecting the system
Geologic inhomogeneities (differences in structure, lithology, climate, etc.)
Other Fundamental concept of geomorphology
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Time and history: landforms evolve through time. The age of the structure, length of time
one or more processes have been in effect, and the sequences of geologic events all play a
role in the evolution of a landscape.
Response: Landforms are part of a system that reacts and changes to external forces.
o Related concepts:
 Lag time: The time it takes for a landform to change in respond to a new
set of conditions
 Relict landform: A landform formed under a previous condition. (e.g. New
England's drumlins and other glacial features.)
Equilibrium (self-regulation, homeostasis)
o Perception of equilibrium state is a function of time:
 Static Equilibrium: no perceived change
 Steady State Equilibrium: Fluctuation about a mean
 Dynamic Equilibrium: Fluctuation about a moving average
 Dynamic Metastable Equilibrium: Fluctuation about a moving average
marked by discontinuities
Feedback:
o negative feedback: reduces or alters
o positive feedback : enhances or exacerbates
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Some general classification landforms based on processes
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Constructional vs Destructional
o Constructional
 Depositional processes: alluvial fans, deltas, etc.
 Endogenic processes: responsible for orogenies and regional uplifts that
form most constructional landforms
 - Are there exceptions?
o Destructional
 Processes involving the removal of material such as weathering and
erosion--most exogenic processes
 Local events related to endogenic processes: certain types of explosive
events
Evolution of Geomorphic Theory and the introduction of important concepts
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Catastrophism: 18th and 19th centuries: Landscape had an innate permanence changed
only by catastrophic events.
Uniformitarianism (Hutton, 1785; Playfair, 1802, Illustrations of the Huttonian Theory
of the Earth, Lyell, 1830, Principles of Geology:(cf. Darwin, 1859, Origin of the
Species).
o The present landscape can be explained by processes now observable.
Geologic exploration by post Civil War geologist, western US--These geologists laid
the ground work for Davis' work on cycles of erosion. Gilbert and Powell detailed the
effects of streams and outlined the first geomorphic classifications of streams.
o C Gilbert (1843-1918) introduced the concept of self-regulating equilibrium
landforms, such as graded streams. [G. C. Gilbert, 1914, Report on the Geology
of the Henry Mountains]
o John Wessley Powell (1834-1902)--descriptive classification of streams; concept
of base level; elaborated on the progressive erosion of mountain ranges
Glaciation, Louis Agassiz, 1840, Etudes sur les Glaciers--made popular the theory of
continental glaciation
Landscape evolution (Historical approaches)
o William Morris Davis (1850-1934): cycles of erosion
o Walther Penck: The relative rates of processes (e.g. rate of uplift vs rate of
denudation) controls landscape morphology (1894)
Morphometrics: The application of statistics and mathematics to the analysis of
landforms
o e.g.Horton, 1954, Erosional development of streams and their drainage basins:
GSA Bulletin, v. 82, p. 275-370.
Systems approach:
o Modern geomorphologist view a landform assemblage as an intricate system that
can be studied by analyzing the variables or components that compose it.
o The forces producing change (e.g. energy), the materials upon which the forces
act (and their resistance to change), and the processes by which the change is
produced are all considered.
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Viewing landscapes as fractals:
o Fractals: Objects exhibiting increasing detail with increasing magnification.
Fractals are self similar in that the pattern viewed under magnification is similar
to that of the whole.
o All landscapes have fractal elements.--That's why a scale is important
 Examples: drainage networks, coastlines, sedimentary layers, etc.
References
Bloom, Arthur. 1998, Geomorphology, A systematic analysis of Late Cenozoic landforms, (3rd
edition): Prentice Hall, Upper Saddle River, N.J., 482 p.
Chorley, R.J., Schumm, S.A., Sugden, D.E., 1984, Geomorphology: Methuen and Co. Ltd.,
London, 605 p.
Easterbrook, Donald J., 1993, Surface Processes and Landforms: Macmillan Pub. Co., 520 p.
Hart, M.G., 1986, Geomorphology pure and applied: George Allen And Unwin, Boston MA, 227
p.
Leopold, L.B., Wolman, M.G. and Miller, J.P., 1964, Fluvial processes in geomorphology.
Freeman and Co., San Francisco, 522 p.
Mayer, Larry, 1990, Introduction to Quantitative Geomorphology: Prentice Hall, Englewood
Cliffs, NJ, 380 p.
Morisawa, Marie, 1988, The Geological Society of America Bulletin and the development of
quantitative geomorphology: GSA Bulletin, v. 100, p. 1016-1022.
Morisawa, Marie, 1985, Rivers: Longman Inc., New York, 222 p.
Ritter, D.F., Kochel, C.R., and Miller, J.R., Process Geomorphology (3rd Edition): Wm.C.
Brown Publishers, Dubuque, IA, 544 p.
Summerfield, M.A., 1991, Global Geomorphology. John Wiley and Sons, New York, NY, 536 p.
Thornbury, William D., 1969, Principles of Geomorphology (2nd edition): Wiley and Sons, New
York 594 p.
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