Géomorphologie quantitative - Université de Montpellier · Géomorphologie quantitative. 2 True /False 1. Geomorphology is the study of process working on landforms 2. Surface features

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GGééomorphologie omorphologie quantitativequantitative

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True /False

1. Geomorphology is the study of process working on

landforms

2. Surface features of the earth were commonly attributed

to catastrophic events

3. Climate dominates landscape evolution

4. Most landscapes are Quaternary

5. There are simple explanations for most landforms

6. Enhanced erosion can drive uplift mountain summits

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Overview

What is Geomorphology ?

Relevance of Geomorphology

Development of Geomorphology

Terminology and definitions

Process Geomorphology

Some modern controversies

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What is geomorphology ?

GeomorphologyGê : Earth

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Morphê : Form

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Morphê : Form

Logos : Study

The study of landforms on or near the Earth’s surface and the processes working on them.

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Relevance of geomorphology

People live on landforms and their lives are affected (sometimes catastrophically) by geomorphic processes

Slope determines whether soil accumulates and makes arable land

Slope stability controls landslidesMountains drastically affect the

weather: rainshadows, monsoonsErosion-sedimentation have a

large impact on the carbon cycle

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Relevance of geomorphology

Human action is one of the major processes of geomorphic evolution

People have been building terraced hillsides for thousands of years

People dam rivers, drain groundwater, engineer coast-lines

People plant or burn vegetation on a huge scale

People are paving the worldPeople are changing the

climate

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Geomorphology relates to all the other disciplines of geology in two directions:

–Tectonics, petrology, geochemistry, stratigraphy, and climate determine the geomorphology of the earth and its regions by controlling the principal influences on landscape.

–Therefore evidence from observations of the landscape in turn constrain the tectonic, petrologic, geochemical, stratigraphic, and climatic history of the earth and its regions.

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Tectonic motions create geomorphic features like fault scarps and grabens; from observation of scarps and grabens we infer the sense of tectonic motions and something about their ages.

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Volcanic activity creates calderas; from the form of the caldera we learn about the mechanism of eruption.

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Granite weathers to rounded jointstones; from observation of the shape of boulders and outcrops we can quickly map granite plutons; from the shape of these rocks we infer how they joint and how they chemically weather

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Resistant and weak strata determine the shapes of cliffs; from distant observations of cliff shapes and local knowledge of stratigraphy, we can map outcrops as far as the eye can see

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Glacial processes create geomorphic expressions such as moraines; from the position, form, and age of the moraines we learn about paleoclimate and the nature of glaciers

Mapping the 1890 thrust moraine of Brúarjökull. Photo: Ólafur Ingólfsson 2004.

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Arid land geomorphology

Coastal geomorphology

Tectonic landforms

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What is geomorphology ?Fluvial processes and landforms

Karst processes and landforms

Eolian processes

Glacial erosion and landforms

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What is geomorphology ?Chemical

weathering and soils

Physical weathering

Mass movement and slopes

Drainage basins

Glaciers and glacial mechanisms ✔

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What is geomorphology ?Dating of geomorphic features

Field trip – Regional geomorphology

Landscape evolution modeling

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Géomorphologie

http://www.gm.univ-montp2.fr/spip/spip.php?article1004

Alfredo Taboada

Rodolphe Cattin

Jean-François Ritz

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Date Lieu Enseignement Horaire Enseignant

12/03 M2A Introduction 10h00-12h00 cours Cattin

13/03 M2A Processus de versant 9h00-12h00 cours Cattin

14/03 M2A Instabilité de pente 9h00-12h00 cours Taboada

15/03 Bat 22 1er salle info Modélisation 9h00-12h00 Cattin

19/03 M2A Dynamique des rivières 9h00-12h00 cours Cattin

20/03 M2A Incision fluviale 9h00-12h00 cours Cattin

22/03 Case Courrier Cattin Remise du devoir 18h00

26/03 M2A Diffusion 9h00-12h00 TD Taboada

28/03 M2A Morphotectonique 9h00-12h00 cours Ritz

3-4-5/04

St Bauzille-de-Putois

Sorties terrain - Photo Aérienne et Carte

Cattin Ritz Taboada

16/04 Bureau Cattin Remise du rapport 18h00

18/04 M2A Examen 2h

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In the 17th & early 18th century, surface features of the earth were commonly attributed to catastrophic, often biblical-like events; A school of thought referred to as "catastrophism"

Georges Cuvier, 1768-1832

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During the late 18th & 19th century, the works of Hutton, Playfair, & Lyell introduced the concept of“uniformitarianism”: "the present is the key to the past."

James Hutton, 1726-1797. Sir Charles Lyell, 1797-1875 John Playfair, 1748-1819

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By the late 19th century, Gilbert postulated that landforms reflect a state of balance between the processes that actupon them and the structure and composition of the rocks that compose them

Grove Karl Gilbert, 1843 - 1918 Terraces marking former strand lines of Lake Bonneville on hillside atBonneville Salt Flats, western Utah. Image date Oct. 2006

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But geomorphologists were “lured away”by the Davisian model of landform development

William Morris Davis, 1850-1934

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In Davis’s models tectonic forcing is an impulsive event that occurs at the beginning of the “geomorphic cycle”.

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Walther Penck , 1888-1923

Penck suggested a more wave-likepattern of tectonic forcing through time

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John Hack proposed that, when rate of deformationare sustained for a long intervals, landscapes willcome into a sort of balance or dynamic equilibrium.

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By the mid 20th century, there was a return to theimportance of the relationship between form and process, fuelled in large part by the “quantitative revolution”.

A. Faraud Mountain, Dévoluy, SE France. B. Associatedexperimental modeling (Bonnet & Crave, Geology, 2003)

A

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Terminology and definition

Agents“that which acts or has the power to act”Water, wind, ice…

Processes“progressive steps by which an end is attained”Weathering, erosion, transport, deposition

EnergySolar, geothermal, gravitational, chemical

Systems“an assemblage of parts forming a whole”Fluvial, glacial, coastal

ClimateDetermines dominant agents

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TimeEvolution of landforms/landscapes

ThresholdA condition that must be exceeded in order for state to change within the system

FeedbackPositive – self-reinforcing; acceleratingNegative – self-regulating; damping

EquifinalitySimilar final states achieved through different mechanisms

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Steady-stateA time-invariant condition

Dynamic equilibriumState changes around a central point

Change

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The concept of “dynamic equilibrium” was re-born, as landforms were seen as adjusting to the processes operating on the geology and consequently, processand form share a “cause and effect relationship”. The emphasis on “form and process” led to the development of “Process Geomorphology”.

ExogenicprocessesWeathering,

transport, erosion, sedimentation

Endogenic processesTectonic, isostasy

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A delicate balance or equilibrium exists between landforms and process.

The perceived balance between process and form is created by the interaction of energy, force, and resistance.

Changes in the balance between driving and resisting forces may destabilize the system. The system may cross a threshold, and may initiate a new pattern of equilibrium.

Various processes are linked in such a way that the effect of one process may initiate the action of another

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Main drainage basins in France

Main drainage basins in Hérault

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Geomorphic elements of a drainage basin, Burbank & Anderson, 2001

• River channels• Hillslopes• Crests of interfluves• Drainage divide

Some of theseelements will respondmore rapidly to changes imposed on them than will others

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The perceived balance between process and form is created by the interaction of energy, force, and resistance.

Force F = m aweight = mass * gravityA measurement of force is Newton

Energy (or work) = force*distance = mass *gravity *htF * d m * a *ht

A measurement of energy is Joules

Driving Forces: Climate, Gravity, Forces generated inside the earthResistance: Provided by the geologic framework

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Thresholds Changes in the geomorphic system when the limits of equilibrium are exceededa. Extrinsic Thresholds: caused by external controlling factorsb. Intrinsic Thresholds: usually caused by internal factors.

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Before After

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Process GeomorphologyVarious processes are linked in such a way that the

effect of one process may initiate the action of another

Gabet et al., Geomorphology, 2004Burtin et al., JGR, 2009

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Processes are multivariate and interrelated

Different time frames for the study of geomorphic

systems

Complexities: Thresholds, stores, non-linear

relationships, multiple relationships

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Philip England

Peter Molnar

P. Molnar and P. C. England. Late Cenozoic uplift of mountain ranges and global climate change: chicken or egg. Nature, 346:29-34, 1990

How do we tell whether the climate caused uplift of the summits or whether surface uplift of the ranges causedchanges in climate ?

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How do you determine mean elevation in the past ?During Ice Age time, was there more precipitation or less ?Can enhanced erosion drive uplift of montain summits ?

Burbank & Anderson, 2001

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What controls the ultimate height of mountains ?Are surface processes capable of eroding at several

mm/yr ?Or rapid rates of rock uplift are commonly compensated by

events of tectonics erosion (extensional faulting) ?

Comparison between the heights of Mt. Everest on Earth, Maxwell Montes on Venus and Olympus Mons on Mars

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References

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True /False

1. Geomorphology is the study of process working on

landforms

2. Surface features of the earth were commonly attributed

to catastrophic events

3. Climate dominates landscape evolution

4. Most landscapes are Quaternary

5. There are simple explanations for most landforms

6. Enhanced erosion can drive uplift mountain summits

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Géomorphologie quantitative - Université de Montpellier · Géomorphologie quantitative. 2 True /False 1. Geomorphology is the study of process working on landforms 2. Surface features