- Text: Bloom, Arthur, 2004, Geomorphology: Chapters
From Space: Introduction: Regional Landforms Analysis and
Geomorphological mapping (Optional)
landform, landscape, endogenic, exogenic, equilibrium, lag
time, relict landscape, lithology, structure, catastrophism,
uniformitarianism, dynamic equilibrium, steady state, isostatic,
positive and negative feedback. relict landform, lag time,
orogen, fluvial, aeolian, base level, graded stream
: (Geo, G. the Earth; Morph, G. Form, ology G.
the science of) Geomorphology is the study of landscapes--It entails
the systematic description of landforms and the analysis of the
processes that create them. Geomorphologists are also concerned
with understanding the function landforms and how landforms respond
to changes in energy. Because landforms and landscapes result
from the combined effects of lithology, structure, and process,
geomorphology draws upon nearly all fields of geology.
- A Landform is an individual feature,
such as a slope, valley or mountain
- Landscape is the he combined effect
of numerous landforms, such a mountainous or desert
The three independent variables that control landscape
are climate (precipitation
and temperature), plate tectonics, and history
In the long term these factors control structure, lithology,
and process, the three dependent
variable that landscapes reflect most closely. A common
way of viewing landscape variables is outlined below as the interplay
between energy, process, and resisting
framework. How you approach
a landscape will depend on the time frame you are considering. Energy,
process, and sediment supply are important to a geologist studying
a beach. However,
a geomorphologist studying the Rocky Mountains might focus on tectonic
setting, climate, and process over the course of
the last billion years.
1. Energy: Energy drives geomorphic
change and is the force behind process. These energy sources (listed
below) drive convection in both the atmosphere and the earth, and
drive chemical reactions. Without energy we would not have the hydrologic
cycle, weathering, or the tectonic activity that characterize earth
- Solar energy:
Drives climate and exogenic processes
- 2 cal/cm2-min reaches the outer atmosphere.
- 30 to 14 % is absorbed into the system--depending on latitude
- Solar energy and its interactions with the earth's surface,
the atmosphere, and the hydrosphere determines climate,
the mean weather condition experienced by a given region.
- Geothermal energy: Drive Plate Tectonics and endogenic
- derived from decay of radioactive elements and residual
- gradient ± 20-30°C/km (crust)
- Gravity: Drives convection, which is important to everything
- g= acceleration due to gravity = 980 cm/sec2 or
2. Process: How energy is applied:
The processes that shape the landscape fall into two broad categories. Endogenic
processes are largely driven by internal convection and adjustments
caused by the redistribution of heat and mass. Exogenic processes
operate on the earth's surface and are driven by solar energy with
the aid of water.
- Endogenic processes: Processes that operate
from within the earth.
- Tectonics processes: Plate tectonics (e.g.
orogenic processes and rifting)
- Volcanism: Intraplate hotspot activity (lava
plateaus and volcanoes) arc volcanism, sea-floor spreading
- Isostacy Animation
- Epeirogenic processes: regional uplift
and subsidence caused by mantle anomalies.
- Isostastic processes: local subsidence
and uplift caused by local loading and unloading
- Exogenic processes : These processes operate
on the earths surface.
- weathering and erosion
- hydrologic cycle and related fluvial processes
- aeolian activity
- biological activity and man (?)
- Extragenic (my term)--meteor impact
- Addition of water (?) from comets?
- Impact structure
3. Resisting framework: lithology
With the exception of delta plains, basin and similar deposition
settings, most landscapes are largely denudational, created through
the erosion of pre-existing features such as a plateaux, fold belts,
sedimentary deposits, or plutons that provides a resisting framework
that exogenic processes shape and reform to produce a landscape. The
two most important elements forming this framework are lithology
- lithology affects how much energy or time is required
to produce change.
- Structure determines the grain of the topography (joints,
fold patterns, layering, arrangement of rocks of varying resistance)
Water plays a key role in the earth's geomorphic processes in the
- it is the principle agent of weathering: a catalyst for reactions
and universal solvent
- through the hydrologic cycle enables energy from the sun to be
converted to potential and kinetic energy required to eroded mountains
- beneath the earth water affects faulting the production of magma
and metamorphic reactions.
- circulates heat through the oceans and atmosphere -strongly influences
Scale: Typically a large feature such
as a mountain massif is more persistent than a small rocky spire
because more energy and time is required to modify it. Baker's
classified of landforms by size (Table 1) is a useful display of
this relationship. However, permanence in fact is a
function both the size of the feature and its resistance to
the processes acting on it. For example a glacial striation may
be ground down within a day beneath a glacier, but once exposed
may persist for a hundred years or more. Likewise drumlins
may persist for thousands of years once removed from the activity
of flowing ice and glacial metwater streams.
|Table 1. Classification of terrestrial landforms
based on scale and their approximate persistence (After
||continents and ocean basins
| ~1,000,000 km2
||Shields and provinces
|| Major valley, large delta
||Individual mountain, large alluvial fan
||Hillslopes, stream channel, estuary, barrier island
||small tributary channels, drumlin
||point bar , gully, glacial groove
Geologic history: (relaxation time of
past events): Not all features are the product of current processes.
Landscapes evolve over millions of years under ever changing conditions.
Age, structure, resistance, climate and past geologic
events all play a role. Although glaciers retreated
12,000 years ago many glacial features persist. They have not yet
been removed by today's processes. Glacial drumlins on the North
Shore and cirques in the White Mountains are relict landforms,
formed under a previous condition. Lag time is
the time required for a landform to change in response to changing
conditions. Moraines forming Cape Cod change rapidly in response
to wave activity and rising sea level, whereas a glacially scoured
rocky coast may take thousands of years. As discussed above,
such variation in lag time reflect the resistance of the landform
and the nature and intensity of the processes acting upon it.
Equilibrium: (self-regulation of energy)
Landforms adjust in response to available energy and mass input. A
storm introduces energy and mass to a drainage basin. In response
streams will deep their channels and widen their banks to expend
energy and accommodate increased flow. In the summer, deposition
changes the channel to accommodate lower flows and decreased energy
inputs. The stream therefore is self regulating, adjusting
it's channel to handle the available input. A barrier island is
another example of a self-regulating landform. By inlet migration
and overwash an inlet can migrate to keep up with rising
sea level, unless inhibited by jetties and seawalls. Eventually
a critical threshold is reached and a system experiences a rapid
change to a new set of conditions.
Perception of equilibrium
state is a function of time:
- Static Equilibrium: no perceived
- Steady State Equilibrium: Fluctuation
about a mean
- Dynamic Equilibrium: Fluctuation
about a moving average
Figure 1. Two common view of equilibrium.
- negative feedback: reduces or alters
- positive feedback : enhances or exacerbates
Feedback mechanisms are extremely important in considering climatic
changes and the processes that drive
Catastrophism: A prominent concept in the
18th and 19th centuries, catastrophism considered landscapes to have
an innate permanence changed only by catastrophic events. The theory
was set aside with the acceptance of uniformitarianism but has resurfaced
as we begin to understand the relationship between meteor impacts
and mass extinctions.
Uniformitarianism and landscape evolution
Uniformitarianism is the principle that features on the earth form
not by catastrophic events but evolve through the action of gradual
processes observable today and occurring over a seemingly limitless
period of time. The concept was the foundation that allowed others
to investigate landscape evolution. "The past is the key
to the present" and "geologic time" all evolved from
Hutton's doctrine of uniformitarianism.
- The principal players in the evolution of uniformitarianism were:
Hutton (1726-1797) Scottish naturalist: 1785 first
formulated the law and published it in The
Theory of the Earth. For more on Hutton and to read
his abstract first presented April 4, 1785, during a meeting
the Royal Society of Edinburgh click
here (Department of Geograpy-Geology,UW Marathon).
(1748–1819) Scottish scientist and mathematician: 1802,published Illustrations
of the Huttonian Theory of the Earth, a book elucidating
Charles Lyell (1797-1875) British Lawyer and Geologist:
Known of as the father of geology. Published Principles
of Geology in 1830 (cf. Darwin, 1859, Origin
of the Species) in which he promulgated the theory to a
- Geologic exploration by post Civil War geologist in the western
US: The post-civil war era was a time of geologic enlightenment. Westward
migration lead to the discovery and exploration of unique and
expansive territories that needed to be inventoried and studied. Investigations
led to a blossoming of new ideas that outpaced the ensconced
beliefs of European thinkers. Even Swiss naturalist, Louis
Agassiz, who developed the glacial theory, moved to the US to
take position at Harvard and explore his new idea. Grove
Karl Gilbert and John Wesley Powell detailed the effects of streams
and outlined the first geomorphic classifications of streams.
These geologists laid the ground work for Davis' work on cycles
of erosion and for future geomorphological investigations.
- Grove Carl
Gilbert (1843-1918) is the father of modern geomorphology.
His greatest contribution was in fluvial geomorphology. He
introduced the concept of self-regulating equilibrium landforms,
such as graded streams, described the structure of deltas and
preformed the first quantitative studies of streamflow in
flumes. He first described the laccoliths of the Henry Mountains,
the block-faulted nature of the Basin and Range, and pluvial
Lake Bonneville, located in the Great Salt Lake basin, Utah
during the Pleistocene. [G. C. Gilbert, 1914, Report
on the Geology of the Henry Mountains]
Wesley Powell (1834-1902) is most famous for his
excursion down the Colorado River. He developed a descriptive
classification of streams, defined the concept of base
level, and elaborated on the progressive erosion of mountain
- Clarence E,
Dutton (1841-1912) studied in detail the features
of the Colorado Plateau, pioneered seismology and evolved
the modern concept of isostacy and its importance to geology.
- Continental Glaciation
Agassiz (1807–1873) was a Swiss born zoologist
who developed the modern theory of continental glaciation
in his Etudes sur les Glaciers (1840). In
1947 he accepted a position at Harvard where he could more
openly pursue his interests in glacial studies.
- Landscape evolution: Historical approaches
Morris Davis (1850-1934): Cycles
- Walther Penck (1888-1923): German Geomorphologist.
The relative rates of processes (e.g. rate of uplift vs rate
of denudation) controls landscape morphology (1894)
- Lester King worked largely in South Africa. Published Canons
of Landscape Evolution (1953) in which he discussed
the roles of process, time, and structure in the formation
of landscapes and evlolution of slopes.
Complex history of Landscapes
Rarely does a landscape represent a a single process,
event, or progressive uninterrupted evolution of events, as inferred
by Davis. Like rocks landscapes are recycled, experiencing
multiple events of uplift, erosion, denudation, subsidence, deposition,
and deformation. However, unlike a rock, a landscape retains
aspects of the texture, structure and compost ion of the landscape
before it. The Southern Rocky Mountains are a good example. They
have been uplifted and eroded (peneplained) no less than three times. Old
faults are reactivated by new tectonic forces and older rocks are
progressively unroofed adding their framework to the new landscape.
The present Rockies are less than 5 million years old, but are cored
by rocks nearly 2 billion years old. The flat upland surface of the
southern Rockies is attributed to a previous peneplained surface
that once lay close to sea level but now lies nearly 10,000 feet
|Figure 2. The landscape cycle (c.f. the rock cycle). Landscapes
are a palimpsest of numerous events, each adding an aspect to
to the present day terrain.
Modern geomorphologist view a landform assemblage as an intricate
system that can be studied by analyzing the variables or components
that compose it. 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. Many geomorphic system are inter-connected and often
the mistake is make by treating them separately.
With the advent of air photography, satellite imagery and GIS geologists
are able to view and analyze large scale (first and second order)
features from an entirely new perspective. This approach has been
particularly important in the exploration the Earth, Mars and other
Charles Lyell, Understanding Evolution, University of California
Museum of Paleontology URL:http://evolution.berkeley.edu/evosite/history/uniformitar.shtml
of Landscape Evolution, Geography 423 Advanced Geomorphology,
D.J. Sauchyn, University of Regina, CA, URL: http://uregina.ca/~sauchyn/geog423/models.html
Beyond the Plateau,
a biography of Powell by the Smithsonian, URL: http://www.150.si.edu/chap3/plateau.htm
of John Wesley Powell: NPR Radio audio URL:http://www.npr.org/programs/atc/features/2003/aug/water/part1.html
Puzzles and Discussions
Addtional questions related to
- Why does Bloom not title his book a Systematic Analysis
of Landforms? Why does he stress "Late Cenozoic" landforms?
- How does Plate Tectonics affect climate?
- What is the relationship between CO2 and weathering
- Can you find and describe any examples of positive and
- Baker, V.R., 1986, Introduction: Regional landforms analysis,
in Short, N.M., and Blair, R.W., Jr., eds., Geomorphology
from Space A global overview of regional Landforms. URL: http://disc.sci.gsfc.nasa.gov/geomorphology/GEO_1/GEO_CHAPTER_1.shtml
- Bloom, Arthur. 1998, Geomorphology, A systematic analysis of
Late Cenozoic landforms, (3rd edition): Prentice Hall, Upper Saddle
River, N.B., 482 p.
- Bourgeois, Joanne, 1998, Model Survey Geologist: G. K. Gilbert,
GSA Today, p. 16-17. http://socrates.berkeley.edu/~geomorph/Bourgeois_GKG.pdf)
- 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.
- Gohn, Kathleen K., 2004, Celebrating 125 Years of the U.S. Geological
Survey, U.S. Geological Survey, Reston, Virginia: 2004 (pdf)
- 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.
- Pidwirny, Michael J., 1996-2001, Fundamentals
of Physcial Geography, http://www.geog.ouc.bc.ca/physgeog/contents/4f.html
- Ritter, D.F., Kochel, C.R., and Miller, J.R., 2002, Process Geomorphology
(4rd Edition): McGraw Hill, 576 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.
- Twidale, C.R., 2003, "Canons” revisited and reviewed:
Lester King's views of landscape evolution considered 50 years
Geological Society of America Bulletin 2003 115: 1155-1172
Historic Documents available on the Internet
Dutton, Capt. Clarence E, 1881, The
physical geology of the Grand Canyon District, , Ordnance Corps.
U.S.A. From Annual report of the United States Geological Survey
to the Secretary of the Interior, 1880-81, pp. 47-166 (Available
through Library of Congress) http://memory.loc.gov/cgi-bin/query/r?ammem/consrv:@field(DOCID+@lit(amrvgvg40)):
Powell, Capt. John Wesley,1895, Canyons
of the Colorado it is (Available through Project Gutenberg)
___ 1875, Exploration
of the Colorado River of the West and Its Tributaries Explored
in 1869, 1870, 1871, and 1872 (Available through the Marriot
Library Digital Collection) @http://content.lib.utah.edu/cdm4/document.php?CISOROOT=/Powell&CISOPTR=365&REC=1
of Geological Sciences/Salem