Géomorphologie
quantitative
1
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
2
Overview
What is Geomorphology ?
Relevance of Geomorphology
Development of Geomorphology
Terminology and definitions
Process Geomorphology
Some modern controversies
3
What is geomorphology ?
Geomorphology
Gê : Earth
4
What is geomorphology ?
Morphê : Form
Geomorphology
Gê : Earth
5
What is geomorphology ?
Morphê : Form
Geomorphology
Gê : Earth
Logos : Study
The study of landforms on or near the Earth’s surface
and the processes working on them.
6
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 landslides
Mountains drastically affect the
weather: rainshadows, monsoons
Erosion-sedimentation have a
large impact on the carbon cycle
7
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 coastlines
People
plant
or
burn
vegetation on a huge scale
People are paving the world
People are changing the
climate
8
What is geomorphology ?
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.
9
What is geomorphology ?
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.
10
What is geomorphology ?
Volcanic activity creates calderas; from the form of the
caldera we learn about the mechanism of eruption.
11
What is geomorphology ?
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
12
What is geomorphology ?
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
13
What is geomorphology ?
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
14
Mapping the 1890 thrust moraine of Brúarjökull. Photo: Ólafur Ingólfsson 2004.
What is geomorphology ?
Coastal geomorphology
Arid land geomorphology
Tectonic landforms
✔
15
What is geomorphology ?
Fluvial processes and landforms
Glacial erosion and landforms
✔
Eolian processes
Karst processes and landforms
16
What is geomorphology ?
Chemical
weathering and
soils
Physical weathering
Drainage basins
✔
Mass movement and slopes
Glaciers and glacial mechanisms
✔
17
What is geomorphology ?
Dating of geomorphic features
✔
Field trip – Regional geomorphology
✔
Landscape evolution modeling
✔
18
Géomorphologie
Alfredo Taboada
Jean-François Ritz
Rodolphe Cattin
http://www.gm.univ-montp2.fr/spip/spip.php?article1004
19
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
3-45/04
St Bauzille-dePutois
Sorties terrain - Photo Aérienne
et Carte
16/04
Bureau Cattin
Remise du rapport
18h00
18/04
M2A
Examen
2h
Cattin Ritz
Taboada
20
Development of Geomorphology
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
21
Development of Geomorphology
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.
John Playfair, 1748-1819
22
Sir Charles Lyell, 1797-1875
Development of Geomorphology
By the late 19th century, Gilbert postulated that landforms
reflect a state of balance between the processes that act
upon 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
23 at
Bonneville Salt Flats, western Utah. Image date Oct. 2006
Development of Geomorphology
But geomorphologists were “lured away”
by the Davisian model of landform
development
William Morris Davis, 1850-1934
24
Development of Geomorphology
In Davis’s models tectonic forcing is an impulsive
event that occurs at the beginning of the
“geomorphic cycle”.
25
Development of Geomorphology
Penck suggested a more wave-like
pattern of tectonic forcing through time
Walther Penck , 1888-1923
26
Development of Geomorphology
John Hack proposed that, when rate of deformation
are sustained for a long intervals, landscapes will
27
come into a sort of balance or dynamic equilibrium.
Development of Geomorphology
A
By the mid 20th century,
there was a return to the
importance
of
the
relationship between form
and process, fuelled in
large
part
by
the
“quantitative revolution”.
A. Faraud Mountain, Dévoluy, SE France. B. Associated
experimental modeling (Bonnet & Crave, Geology,
282003)
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
Energy
Solar, geothermal, gravitational, chemical
Systems
“an assemblage of parts forming a whole”
Fluvial, glacial, coastal
Climate
Determines dominant agents
29
Terminology and definition
Time
Evolution of landforms/landscapes
Threshold
A condition that must be exceeded in order for state
to change within the system
Feedback
Positive – self-reinforcing; accelerating
Negative – self-regulating; damping
Equifinality
Similar final states achieved through different
mechanisms
30
Terminology and definition
Steady-state
A time-invariant condition
Dynamic equilibrium
State changes around a
central point
Change
31
Process Geomorphology
The concept of “dynamic equilibrium” was re-born, as
landforms were seen as adjusting to the processes
operating on the geology and consequently, process
and form share a “cause and effect relationship”. The
emphasis on “form and process” led to the
development of “Process Geomorphology”.
Exogenic
processes
Weathering,
transport, erosion,
sedimentation
Endogenic processes
Tectonic, isostasy
32
Process Geomorphology
33
Process Geomorphology
34
Process Geomorphology
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
35
Process Geomorphology
A delicate balance or equilibrium exists between
landforms and process.
Main drainage basins in France
Main drainage basins in Hérault
36
Process Geomorphology
A delicate balance or equilibrium exists between
landforms and process.
• River channels
• Hillslopes
• Crests of interfluves
• Drainage divide
Some
of
these
elements will respond
more
rapidly
to
changes imposed on
them than will others
Geomorphic elements of a drainage basin, Burbank & Anderson, 2001
37
Process Geomorphology
The perceived balance between process and form is
created by the interaction of energy, force, and resistance.
Force F
=ma
weight
= mass * gravity
A measurement of force is Newton
Energy (or work) = force*distance = mass *gravity *ht
F*d
m* a
*ht
A measurement of energy is Joules
Driving Forces: Climate, Gravity, Forces generated
inside the earth
Resistance: Provided by the geologic framework
38
Process Geomorphology
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.
Thresholds Changes in the geomorphic system when
the limits of equilibrium are exceeded
a. Extrinsic Thresholds: caused by external controlling
factors
b. Intrinsic Thresholds: usually caused by internal
factors.
39
Process Geomorphology
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.
Before
After
40
Process Geomorphology
Various processes are linked in such a way that the
effect of one process may initiate the action of another
Gabet et al., Geomorphology, 2004
Burtin et al., JGR, 2009
41
Process Geomorphology
Processes are multivariate and interrelated
Different time frames for the study of geomorphic
systems
Complexities: Thresholds, stores, non-linear
relationships, multiple relationships
42
Some modern controversies
Peter Molnar
Philip England
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 caused
changes in climate ?
43
Some modern controversies
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
44
Some modern controversies
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
45
References
46
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
47