Geomorphic Paradigms and Models in Physical Geography Cycling of Earth Materials Catastrophism Neptunism Vulcanism/Plutonism Uniformitarianism Fluvialism

GEO 513 Geomorphology 1

Geomorphic Paradigms and Models in Physical Geography

• Cycling of Earth Materials• Catastrophism

• Neptunism• Vulcanism/Plutonism

• Uniformitarianism• Fluvialism• Modern Approaches

• Historical• Dynamic• Postmodern

Ryerson University Department of GeographyGEO 513: PHYSICAL GEOGRAPHY IN DECISION SUPPORT

D. BantingRYERSON UNIVERSITY

DEPARTMENT OF GEOGRAPHY


Introduction: Geomorphology

• concerned with• earth materials• form of the land• processes that transform it

• terrestrial landscapes have generally been regarded as static• processes are changes over time

• complex and indiscernible• possibly progressive or cyclical, or even random in variation• understanding depends on the nature and duration of observations and

evidence• we see changes differently, depending on:

• how observant we are• what we expect to see• what changes coincide with our lifetimes

Global Geomorphic Processes: Cycling of Earth Materials • development and destruction of earth materials and forms• from primary minerals and rocks • through transformations and transfers, • returning eventually to magma

Erosion

Subduction to magma

Earth’s surface Deposition

Transportation

Weathering

Subterranean Convection

Solidification of magma

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• the concept of “terra firma” is not ubiquitous; earthquake zones and eroding cliffs are considered anomalies, though they are not really rare

• attitudes of societies may also need to be adjusted to reconcile social institutions, programs and policies with geomorphic propensities for change

• if society is not sensitive to earth processes, there may be a huge social and environmental cost to pay – recent evidence from earthquakes and tsunamis, even volcanic eruptions, slope failures, erosion and flooding

• there are many other geomorphic processes that are more insidious and therefore not as widely recognized

Questions arise about coping with them: • Do sudden catastrophic slope failures impart more social and

environmental damage than gradual downslope displacements? • If so, under what conditions (what locations and materials) are they

occurring? • How can society predict these (when and where) and minimize the risks?


Understanding geomorphology• more than reflecting on huge natural disasters, past, present and future• part of our fundamental need to know where we are, • therefore to systematically describe, explain, predict, and manage our

circumstances

Geomorphology’s geographic dimensions are very significant:• Scale: from global-scale geomorphic materials, forms and processes being

regarded as parts of a grand cycle, to local needs for land management in meeting route and site selections for various land uses: avoid sites too risky to build on

• Themes: linked to other geographic sub-disciplines: backdrop for “the land”, comprising the mountains, hills, plains, rivers, coasts, resource industries (fishing, forestry, agriculture, energy) and therefore the traditions that shape a society…

• Spaces: theoretical and practical understanding of how landscapes express the cumulative impact of current and bygone events (tectonic, fluvial glacial etc) and how these influence developing sustainability

• Embraced in its paradigms (plural)


Paradigms• ways of looking at things• the framework of thinking• provides a context that is important in determining the nature of responses to

problems

• E.g. waste management issues for:• a lawyer, biochemist, dentist…, engineer, waste hauler, economist,

taxpayer, landowner next door to a proposed landfill site • but it is politicians who are empowered to balance these perspectives;

and geographers who provide the synthesis of the data!

In geomorphology: a progression of paradigms from doctrine-driven chauvinism to empirically-based and logical pragmatism, aimed at: understanding the earth

That individuals have changed their adherence to paradigms demonstrates an open-mindedness that is consistent with an applied geographic perspective; may be thematic (like the course outline) or regional (by zones) or historic (changes in perspective)


Catastrophism• maintains a Biblical perspective: the landscape was created by a series of calamitous events• cataclysms destroyed all life and were followed by renewal

The two groups: Neptunists and the Plutonists (named for outdated gods): • Neptunism

• great floods (as in Bible and other cultures' traditions) inundated all land surfaces; left the features now found on the ground

• In European Age of Enlightenment (scientific observation): rock strata were presented as evidence supporting this paradigm

• rocks explained as Great Flood sediments or crystallized deposits precipitated from sea water at the bottom of the expanded sea;

• fossils above sea level were marine at some time

• mountaintop locations were interpreted as confirmation of how much higher the ocean had been

• valleys created by seawater rushing back to the oceans (modern rivers seemed to be too small to have been responsible)


• Plutonism (Latin) (or from the Greeks: Vulcanism)• regarded the earth as essentially having been molded by volcanic activity

• citing biblical evidence and later direct observation from all around the Mediterranean Sea (Pompeii), as well as in other areas

• accounts of lava flows as commonplace, but none so catastrophic as the Biblical interpretation of the earth’s creation

Catastrophism: • biblical belief that creation took place in 4004 BC (Bishop Usher, 1650)

• no scientific reasoning nor a priori independent observation

• alternative perspectives unwelcome

• “Enlightenment” in Europe increasingly challenged this doctrinaire approach


Uniformitarianism• earth scientists were foremost among the scientific community to advocate

the power of reason, objective rationality, observation-based evidence

• began with James Hutton (1795): Theory of the Earth with Proofs and Illustrations

• observation of an exposure of rock strata in Scotland that indicated a sequence of episodes: fluvial deposition, uplift and tilting, erosion, subsidence, re-uplift, and most recently, renewed erosion

• the Earth changes slowly and uniformly by processes occurring today: 6004 years could not be old enough, contradicting existing dogma

• John Playfair (1802) “the present is the key to the past", credited Hutton and

noted that rivers were actually capable of gradually carving out the valleys in which they flow: low magnitude events over long periods of time are creating the landscape

• Charles Lyell (1833) The Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth's Surface, by Reference to Causes now in Operation led to the popularization of uniformitarianism (11 editions by 1872)

• Lyell also inspired and eventually supported Darwin's views on evolution over

time by suggesting that organisms became adapted to their environment

• when Darwin formulated his concept of the evolution of species to include the notion that gradual changes become significant over long periods of time, a controversy was rekindled between religious and scientific explanations of the earth that in some areas persists today


Catastrophism: meteorite impact is responsible for the mass extinctions of species at the end of the Cretaceous Period (65m.y. BP)

Uniformitarian interpretation of these extinctions: a gradual process occurred following an episode of increased volcanic activity and subsequent climatic change

Is a process which lasts a million or more years considered cataclysmic? What about 1000 yr…?


Fluvialism

• largely coinciding with the uniformitarian concept of gradual progressive landscape evolution, but specifically identifying the activity of running water as the primary determinant of landscapes

• J.W. Powell: rivers carve a landscape• being superimposed on the a priori landscape• downcutting to create valleys, to a “base level” (ultimately sea-level)

plain• eroding across mountains

• G.K. Gilbert: river effects are a “dynamic adjustment” between the rate of sediment removal and the transport capacity determined by the gradient of the river; until a “balanced condition” (~equilibrium) is achieved

• ubiquitous water flow raised fluvialism to a widely accepted paradigm for continental down-wearing


Fluvialism

• From the 1880's, the paradigm was largely associated with the Geographic Cycle of Erosion advocated by W.M. Davis:

• a sequence of landscape evolution - youth, maturity and old age - wear down landscapes which had previously been uplifted above base level

• a time-dependent model (“structure, process and stage”) later extended to the progression of landforms attributed to other agents (wind, glaciers, and waves) and materials

• persisted in the literature until the 1960's,

• subsumed by a quantitative approach from the 1950's

• broadened geomorphological concern for natural balances among landscape materials, (land)forms, and processes involving uplift and downwearing (erosion, transport and deposition) and human interference/accommodation

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Modern Approaches• landscapes seen to involve expression of a variety of origins

a) Historical (beyond Davis’s chronological approach to fluvialism)

• physical landscape as a mosaic of terrain units of differing ages, including degrees of current and past geomorphic activity

• analogous with the geological mapping convention, (time scale as the primary classification for legend classes) therefore to understand the landscape is to recognize these distinct units

• e.g. physiographic units in southern Ontario result from differently-aged materials including:• very old (>700 million years, Precambrian) Canadian Shield rocks• much younger (160-600 million years, Palæozoic) rocks associated with

the Niagara Escarpment• unconsolidated sediments deposited by glaciers much later (Pleistocene

Epoch, 10 000 to 2 million years B.P.)• present materials (valley alluvium, shoreline sediment) deposited in the

post-glacial episode (Holocene Epoch, <10 000 yr B.P.)


• evidence of palæo-environmental conditions (temperature, moisture, and sedimentary circumstances) must have been preserved to be recognized

• now rejuvenated interest in establishing patterns of climate changes and expected future conditions

• but recent and resistant landforms are favoured as the most evident on the landscape (older and more erodible features have become more obscured by the action of later processes)

• processes of erosion are also under-represented in past-landscape reconstructions:• gaps in the stratigraphic record (e.g. the hiatus between the Palæzoic and

the Pleistocene) deny inferences about what the episode was like• a true discontinuity in deposition or sedimentation followed by erosion

would have left the same pattern of earth materials

• historical perspective focuses on where materials of different ages are found, and how landscapes have developed over time

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b) Dynamic Approaches• concerned with systems in which matter and energy exchanges and balances

are described, explained and predicted

• the general public’s subjective perception may be to regard the natural landscape as static since little of it changes over the course of people’s lives

• however systematic observations over about 200 years have indicated that it is not truly a condition of static equilibrium

• there are relentless forces impelling earth materials to move

• neither is it truly a dynamic equilibrium, since this implies opposing reversible forces equally exchanging matter or energy

• the nature of change warrants consideration of patterns: • reversible versus irreversible, • progressive versus cyclical versus homeostatic• regular versus inconsistent• rapid versus gradual• exogenous versus endogenous

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• the activity of landscape processes are now referred to as exhibiting a steady state condition:• the rate of additions of mass are in balance with the rate of removals if a system

retains its form• if the form changes, it is because of an imbalance• e.g. on a stream bed, where sediments are being deposited and eroded at the same

rate, the same shape will be retained, despite the passage through of individual particles of sediment;

• as the flow of the stream changes, morphological dimensions may adjust until a new balance is eventually struck

• geomorphic processes are generally not reversible

• most seem to be in a dynamic equilibrium, but this may be a local and temporary component of a much grander evolution of the landscape over time and space (Figure 1)

• dependencies (among materials, forms and processes) are emphasized by this perspective, whether they are:• responses to external influences (climatic change, tectonic activity), or

• due to feedbacks within their own processes (sediments clogging a stream, slowing flow so more sediment subsequently becomes trapped, until a threshold is reached)


• therefore, observation of the landscape indicates that there are relics of past geomorphic events

• the landscape is not in fully adjusted to the current processes acting upon it

• geomorphological processes involve a mix of • high magnitude, low frequency events (e.g. storms, snowmelt, volcanic

explosions) and • low magnitude, high frequency events (e.g. stream “base flow”,

continental down-wearing)

• changes in these magnitudes and frequencies occur not only over time, but also over space, so one approach to understanding geomorphology is to associate its systems to climatic conditions. (The concept of distinctive morphogenetic regions (e.g. the periglacial) is addressed later.)


• paradigms dictate the ways in which issues are addressed• so no one of these is as comprehensive as all of them together• this is one of the issues which have given rise to postmodern philosophy• it includes a rejection of specific paradigms since knowledge is considered unique to

each individual circumstance

It is increasingly being recognized that few of society’s problems are so focussed as to warrant consideration by a single discipline.

c) Postmodernism• Current practice reflects a variety of perspectives, largely associated with

academic specialties such as:

• geography • glacial geomorphology

• geology • historical/structural geology, sedimentology

• geophysics • crustal deformations

• environmental chemistry • ground water quality

• ecology • palæontology


e.g. pre-glacial bedrock gorge lies buried between Toronto and Bradford (Figure 2):• historical approach to understanding landscape (downwearing, marine

sediments, lithogenesis, tectonics, glaciation, modern erosion)• But superimposed streams are gradually wearing down, so a dynamic

approach accounts for balance of runoff variations and the delivery of eroded sediments

Rather than contradicting one another, both these paradigms are useful in developing understanding and appreciation of landscape elements and processes.

Sharpe, D.R., 1980, Quaternary Geology of Toronto and Surrounding Area, Ontario Geological Survey, Preliminary Map P2204, Geological Series. http://www.geologyontario.mndm.gov.on.ca/mndmfiles/pub/data/imaging/P2204/P2204.pdf

Figure 2 Quaternary Geology of Toronto and Surrounding Area


Decision Support

• sensitive management practices incorporate less-invasive structural solutions as well as non-structural solutions, however there are exceptions, and what is left is the legacy of past mistakes

• Decisions would therefore seem to benefit from first establishing what information was needed to understand the specific conditions at a particular location

• then proceeding to develop predictions from across the relevant disciplines

• what has often happened however is that “engineering” and “ecological” perspectives on geomorphological and other environmental problems develop• either in opposition to or in concert with one another

• to “engineer” a solution has traditionally meant building something to stop the problem (e.g. a structure is designed and constructed, to stop natural processes).


Decision Support

• Engineered solutions have often conflicted with an ecological perspective, which indicated that the “structure” (dam, retaining wall, etc.) would be widely disruptive since all (not just geomorphic) systems are related

• Rather than trying to stop a natural process, non-structural (behavioural) solutions should be sought, such as avoiding the area of the problem.

Applied Physical Geography is inherently broad, encompassing the spatial dimension of many other fields

• geomorphological materials, forms and processes provide opportunities and constraints for human activities

• considers critical knowledge to include• not only general principles regarding geomorphology,• but also specific circumstances of the land under consideration• both based on as much direct scientific observation as is available

• is therefore akin to theoretical and practical geographic wisdom


Decision Support

Thomas Kuhn (1962) suggested:

• that paradigms remain static for long periods of time ("normal science")

• once found to be out of touch with current thinking are suddenly replaced ("revolutionary science")

• the cycle is then repeated

It may be that ”normal” Geomorphology is coming to an end; it may be that Geographic Information Systems (GIS) are either demonstrating this or providing a new, broader paradigm.

Many people before have faced the prospect of such a radical paradigm shift. Some have resisted; some have abandoned old perspectives for new ones. Sometimes the revolution fails.

Documents

Geomorphic Paradigms and Models in Physical Geography Cycling of Earth Materials Catastrophism Neptunism Vulcanism/Plutonism Uniformitarianism Fluvialism