Introduction to Geomorphology

Introduction to Geomorphology
Prof. P. K. Mani
ACSS-751
BCKV, WB, India

What is the Geologic Time Scale?What is the Geologic Time Scale?

What does the time scale represent?
 The geologic time scale divides up the history of the earth based on
life-forms that have existed during specific times since the creation of
the planet. These divisions are called geochronologic units (geo: rock,
chronology: time).
 Most of these life-forms are found as fossils, which are the remains or
traces of an organism from the geologic past that has been preserved in
sediment or rock. Without fossils, scientists may not have concluded
that the earth has a history that long precedes mankind.
 The Geologic Time Scale is divided by the following divisions:
 Eons: Longest subdivision; based on the abundance of certain fossils
 Eras: Next to longest subdivision; marked by major changes in the fossil
record
 Periods: Based on types of life existing at the time
 Epochs: Shortest subdivision; marked by differences in life forms
and can vary from continent to continent.
4

What is the Geologic Time Scale,What is the Geologic Time Scale, continuedcontinued??
 Due to the fact that early geologists had no way of knowing how the discoveries of
the Earth were going to develop, geologist over time have put the time scale together
piece by piece. Units were named as they were discovered. Sometimes unit names
were borrowed from local geography, from a person, or from the type of rock that
dominated the unit.
 The earliest time of the Earth is called the Hadean and refers to a period of time for which we have no
rock record, and the Archean followed, which corresponds to the ages of the oldest known rocks on
earth. These, with the Proterozoic Eon are called the Precambrian Eon. The remainder of geologic time,
including present day, belongs to the Phanerozoic Eon.
 While the units making up the time scale are called geochronologic units, the actual rocks formed during
those specific time intervals are called chronostratigraphic units. The actual rock record of a period is
called a system, so rocks from the Cambrian Period are of the Cambrian system.
Examples
 Cambrian: From the Latin name for Wales. Named for exposures of strata found in a
type-section in Wales by British geologist Adam Sedgwick.
 Devonian: Named after significant outcrops first discovered near
Devonshire, England
 Jurassic: Named for representative strata first seen in the Jura Mountains by German
geologist Humboldt in 1795)
 Cretaceous: From the Latin “creta” meaning chalk by a Belgian geologist
4

Geologic Time Scale
Earth age: 4.6 billion years
condensed and congealed from
a nebula
of dust, gas and icy comets.
Scales of Geologic Time
Eons:
Eras:
Periods:
Epochs:
Zoic: life
Protero-: former, anterior
Phanero-: visible to the naked eye
flowering plants
Paleo-: old
Meso-: middle
Ceno-: recent

Eons:
Precambrian: Earliest span of time
Phanerozoic: Everything since
Eras:
Paleozoic
Mesozoic
Cenozoic
Periods:
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
(Missipp. & Pennsylvanian)
Permian
Triassic
Jurassic
Cretaceous
Paleogene
Neogene
Quaternary
Epochs:
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Holocene
We are living in the Phanerozoic Eon, Cenozoic Era, Quaternary
Period, Holocene Epoch……..BUT
Paleozoic
“Age of
Invertebrates”
Mesozoic
“Age of Reptiles”
Cenozoic
“Age of
Mammals”
17

Why Study Geomorphology?
• Understand the presentUnderstand the present
• Interpret the past
• Uniformitarianism
• James Hutton, Charles Lyell
• Example: Charles Darwin and Atolls
• http://en.wikipedia.org/wiki/Atoll
http://en.wikipedia.org/wiki/Uniformitarianism_(science)

Meaning and Scope of Geomorphology
• What is Geomorphology?
• Derived from a Greek word “geo” which is earth and “Morpho” which is
form. Therefore geomorphology is a discourse on Earths Form.
• It is science that treats the general configuration of the earth's surface
in terms of the classification and description of the nature, origin, and
development of landforms and their relationships to underlying structures,
and the history of geologic changes .
• By examining the above definition we can classify geomorphology in to
• Processes or functional Geomorphology
• Historical Geomorphology
• Therefore geomorphology studies form, processes and history about
earth.

Classification of Geomorphology
Geomorphology has got different classification which made the study
about the physical configuration of the earth well-heeled.
Basically geomorphology is classified as functional or process
geomorphology and historical geomorphology.
A. Historical geomorphology: Traditionally, historical geomorphologists
strove to workout landscape history by mapping morphological and
sedimentary features. Their golden rule was the dictum that ‘the
present is the key to the past’.
Some of the most notable scholars in this category are:
William Davis Morris: he developed a theory of “Geographical cycle”
which states that the Geomorphic processes, without further
complications from tectonic movements, then gradually wear down the
raw topography. Uplifting and denudation takes place alternately. In old
ages uplands turn in to plain lands through planation processes.
Walter Penck: he opposes the Daviasian Model by stating uplifting and
denudation happens at the same time.

 According to him (Penck) the continuous and gradual interaction of
tectonic processes and denudation leads to a different model of landscape
evolution, in which the evolution of individual slopes is thought to
determine the evolution of the entire landscape.
 3 slope forms evolve with uplift and denudation rates.
A. Convex slope profile: when uplifting exceeds rate of denudation.
B. Concave slope profile: when denudation exceeds rate of uplifting.
C. Striate slope profile: when denudation and uplifting happens at the
same rate at a time.
B. Modern historical Geomorphology: It relies on various chronological
analyses, particularly those based on stratigraphic studies of
Quaternary sediments, and upon a much fuller appreciation of
geomorphic and tectonic processes. (fig.1)
C. Processes Geomorphology: is the study of the processes responsible
for formation of landforms. Grove Karl Gilbert was the first modern
processes geomorphologist by studying fluvial and its processes on Henry
mountain in Utah, USA and investigated the transport of debris down from
up.

Catastrophism vs.
Uniformitarianism
Paroxysms Same old,
same old
vs.
In geology and geomorphology a planation surface is a large-scale surface that is almost flat with the
possible exception of some residuals hills. The processes that form planation surfaces are labelled
collectively planation and are exogenic (chiefly erosion). Planation surfaces are planated regardless
of bedrock structures.On Earth they constitute some of the most common landscapes.
Peneplains and pediplains are types of planation surfaces planated respectively by "peneplanation" and
"pediplanation surfaces.

Uniformitarianism vs Catastrophism
Uniformitarianism -- actualism -- "the present is the key to the past“ (Geike)

Refers partly to a method
-- study of present-day processes as a means of interpreting past events
-- assumes constancy of physical laws
Refers also to a geologic theory
-- geologic processes are natural (not supernatural), slow, operate unchanged over
long time periods at about the same rate, and deal with the same materials
-- no directionality in geologic time (e.g., earth is not cooling – Kelvin took
exception)
-- Lyell early on rejected the notion of organic change (evolution); later accepted
notion of evolution, but not the process of natural selection
Uniformitarianism: An assumption that the same physical processes active in the
environment today have been operating throughout geologic time
Catastrophism -- recent geological history strongly decoupled from the past
--- geologic history is marked by long periods of quiescence ( period of inactivity or dormancy)
interrupted by catastrophic upheavals of the land and /or inundations by the sea
--- the last catastrophe was often linked with the Biblical flood. Diluvialism. (that the
earth's surface was shaped by the biblical flood)

Scientists make observations of an event or an object and then try to explain those
observations by organizing them into a logical system. As rock bodies can cover extensive
areas and represent vast periods of time, much of geological research cannot be done as
controlled experiments in a formal laboratory setting. In these situations, we rely on the
assumption that physical, chemical and biological laws are constant. That is, the
processes operating today are the same as those that operated in the past. For instance,
since water flows down hill today, it must have done so in the past. Therefore, if we
identify a body of rocks that exhibits characteristics similar to those found in a modern
geological environment, we assume that it must have formed in a similar manner
Uniformitarianism

Catastrophic TheoriesCatastrophic Theories
• Georges Cuvier: Great catastrophic
floods produced unconformities, and carved
Earth’s landscape.

Georges Cuvier (1769-1832), French Paleontologist
-- Cuvier was actually an anatomist by training.
-- History of life on earth was recorded in fossils within rock strata.
-- Described the succession of fossils in Paris Basin.
-- Realized each rock unit had a unique assemblage of fossils.
-- The older the rocks, the fewer the species like those found today.
How did Cuvier arrive at a catastrophist view of earth history?
-- He realized that extinction had been common in past eras.
-- One species would disappear and another arise in the strata.
-- If species do NOT transmute, then catastrophes occur: boundaries.
-- He perceived floods, droughts, etc. between strata.
-- “New” species required successive creations; biologic; higher levels.
-- This dynamism is called catastrophism.
Stratigraphy of the Paris Basin
Megatherium, a giant ground
sloth. Described by Cuvier.

-- Large-scale mechanical violence: volcanism, building of huge mountain chains.
Inferred that sizes of forces must have been uncommonly large; different from
today’s.
Erosion and denudation: apparently huge torrential rains and accompanying
floods. (In geology, denudation involves the processes that cause the wearing away of the Earth's surface by moving water,
by ice, by wind and by waves, leading to a reduction in elevation and in relief of landforms and of landscapes
-- Complete changes in the observable fauna (of great interest to Buckland).
Noted there was an order of succession to fauna found stratigraphically.
Claimed this order followed that of their creation: fish, amphibians, reptiles,
mammals.
“If there is any circumstance thoroughly established in geology, it is, that the
crust of our globe has been subjected to a great and sudden revolution, the epoch
of which cannot be dated much further back than five or six thousand years
ago...” Cuvier’s Essay on the Theory of the Earth.
Two Main Lines of Evidence for Catastrophism

A) Villarrica Volcano, Chile, a volcano without effects of erosion and
denudation
B) Chachahén Volcano, Mendoza Province, Argentina, a volcano with strong
effect of erosion but no denudation
C) Cardiel Lake, Santa Cruz Province, Argentina, a volcanic area under
strong effect of denudation, exposing subvolcanic rock body.[
(In geology, denudation involves the processes that cause the wearing away
of the Earth's surface by moving water, by ice, by wind and by waves,
leading to a reduction in elevation and in relief of landforms and of
landscapes.
Endogenous processes such as volcanoes, earthquakes, and plate tectonics
uplift and expose continental crust to the
exogenous processes of weathering, of erosion, and of mass wasting).

James Hutton
in the field.
James Hutton (1726-1797), Scottish “Gentleman Geologist”
“Hutton’s unconformity at Siccar Point, where
almost- vertical Silurian layers are overlain by
almost horizontal layers deposited about 100
million years later.”
“The present is the key to the past.”
Geike (1905). The Founders of Geology
James Hutton
 Granites form through heat & fusion deep underground, and are later uplifted and
exhumed.
 Landforms are produced by slow, continuous processes.
Uniformatarianism
 Sediments are eroded from landforms, only to be deposited and later lithified into new
rocks.
 There is neither an apparent beginning nor end to landform development.

Hutton’s ProponentsHutton’s Proponents
• John Playfair (1748-1819)
– Illustrations of the Huttonian Theory of the
Earth (1802).
– Streams carve their own drainage systems.
– Stream reaches and maintains equilibrium,
adjusted to local gradient. CONCEPT OF
“GRADED STREAM”
– The Earth is very ancient; ongoing processes
continue to change it.
• Charles Lyell (1797 - 1875)
The Principles of Geology (1833 - 1875)
A strong promoter of Uniformitarian theory
A vehement opponent of Catastrophism

Sir Charles Lyell, born in
Scotland to a wealthy
family.
Pillars of the temple at Pozzuoli
(Italy), from the frontispiece in Lyell’s
Principles of Geology (1832).
Evidence that former sea levels
differ from today’s. Corrosion bands
on each pillar indicate submersion.
After the temple was built, there was
downwarp and later uplift associated
with volcanic activity.
Sir Charles Lyell (1797-
1875), Scottish Geologist
In the 1840s, Lyell traveled to the US and Canada.
Lyell’s
Principles of
Geology came
42 years after
Hutton’s
Theory of the
Earth.

Other Nineteenth CenturyOther Nineteenth Century
European ContributionsEuropean Contributions
• Venetz, and Bernardhi: Moraines and erratics
prove glaciations extended from polar
regions (1832)
• Louis Agassiz : Recognized glacial landforms
in Europe & N. Am.-
introduced the concept of
Ice Ages (1837)
http://books.google.com/books?http://books.google.com/books?
id=d4erqwFkgu4C&pg=PA8&lpg=PA8&dq=id=d4erqwFkgu4C&pg=PA8&lpg=PA8&dq=
Bernhardi+glacier&source=bl&ots=uDleT4Bernhardi+glacier&source=bl&ots=uDleT4
NQiv&sig=OracgXNC5nHLD5FtVwA5JqkvNQiv&sig=OracgXNC5nHLD5FtVwA5Jqkv
WbY&hl=en&sa=X&oi=book_result&resnuWbY&hl=en&sa=X&oi=book_result&resnu
m=1&ct=result#PPA8,M1m=1&ct=result#PPA8,M1

Charles DarwinCharles Darwin
• Recorded his observations
during the voyage of
• “the Beagle.”
• Suggested an origin for atolls
Darwin (voyage of the Beagle, 1835) -- took a copy of freshly published vol. 1
of Principles of Geology with him on the Beagle. He observed an earthquake
in Chile; calculated that the Andes could be raised in ~ 1 Ma.
An atoll is an island formed by a ring-shaped coral reef encircling a lagoon. The word comes from the
language of the Maldives, an island chain in the Indian Ocean famous for gorgeous beaches and coral
reefs.

Mount St. Helen’s
Before
After
Catastrophism vs. Uniformitarianism
Lyell

Davis' Landscape evolution model
An example from
an arid climate.
Davis' idea of a
Peneplain
‘‘Davis' Cycle of erosion

William Morris Davis’s idealized ‘geographical cycle’ in which a landscape evolves through‘life-
stages’ to produce a peneplain.
(a)Youth: a few ‘consequent’ streams , V-shaped valley cross-sections, limited floodplain
formation, large areas of poorly drained terrain between streams with lakes and marshes,
waterfalls and rapids common where streams cross more resistant beds, stream divides broad
and ill-defined, some meanders on the original surface.
(b)Maturity: well-integrated drainage system, some streams exploiting lines of weak rocks,
master streams have attained grade , waterfalls, rapids, lakes, and marshes largely
eliminated, floodplains common on valley floors and bearing meandering rivers, valley no
wider than the width of meander belts, relief (difference in elevation between highest and
lowest points) is at a maximum, hill slopes and valley sides dominate the landscape.
(c) Old age: trunk streams more important again, very broad and gently sloping valleys,
floodplains extensive and carrying rivers with broadly meandering courses, valleys much wider
than the width of meander belts, areas between streams reduced in height and stream divides
not so sharp as in the maturity stage, lakes, swamps, and marshes lie on the floodplains,
mass-wasting dominates fluvial processes, stream adjustments to rock types now vague,
extensive areas lie at or near the base level of erosion.
Holmes (1965, 473

Paradigms (2 of 2)
Process Geomorphology
 (1890) Recognized some Utah landscapes were formed by Pleistocene Lake
Bonneville. Great Salt Lake and Bonneville salt flats are remnants.
 Contributed to the understanding of river incision.
 Identified lunar craters as caused by impacts, and carried out early impact cratering
experiments

Driving forces
> External (climate, gravity)
> Internal (thermal energy from radio
active decay, friction)
and
Resistant forces
> Lithology
 Structure
• 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)
 lithology of a rock unit is a description of its physical characteristics visible at
Driving and Resistant Forces

• Landsurfaces adjust to local geology and dominant processes
• Continuous erosion does not change slope angles, as long as process types
and rates don’t change
• Developed ‘laws’ of landsurface development (incl. driving / resisting
forces)
• Articulated in ‘Report on the Geology of the Henry Mountains’ (1877)
2. G.K. Gilbert’s Delicate Balance
Gilbert, G. K. 1877, Report on the geology of the Henry Mountains [Utah]: U.S. Geog. and Geol. Survey
Rocky Mtn. Region, 100 p.

Feedback model of reciprocal interactions and adjustments between organisms and Earth surface
processes and landforms. The model integrates in an eco-evolutionary framework geomorphic,
ecological and evolutionary processes. Black colour represents physico- chemical elements and
controls. Grey colour represents living organisms and biological controls. Earth surface
processes, landforms and living organisms co-adjust according to feedback mechanisms.

Types of equilibrium in geomorphology. (a) Static equilibrium (b) Stable equilibrium.
(c) Unstable equilibrium. (d) Metastable equilibrium (e) Steady state equilibrium
(f ) Thermodynamic equilibrium (g) Dynamic equilibrium (h) Dynamic metastable

Types of equilibrium in geomorphology.
(a)Static equilibrium occurs when a system is in balance over a time period and no
change in state occurs.
(b)Stable equilibrium records a tendency to revert to a previous state after a small
disturbance.
(c)Unstable equilibrium occurs when a small disturbance forces a system towards
a new equilibrium state where stabilization occurs.
(d)Metastable equilibrium arises when a system crosses an internal or external
system threshold , so driving it to a new state.
(e) Steady state equilibrium obtains when a system constantly fluctuates about a
mean equilibrium state.
(f ) Thermodynamic equilibrium is the tendency of some systems towards a state
of maximum entropy, as in the gradual dissipation of heat by the Universe and its
possible eventual ‘heat death’ and in the reduction of a mountain mass to a
peneplain during a prolonged period of no uplift.
(g) Dynamic equilibrium may be thought of as balanced fluctuations about a mean
state that changes in a definite direction (a trending mean).
(h) Dynamic metastable equilibrium combines dynamic and metastable
tendencies, with balanced fluctuations about a trending mean flipping to new
trending mean values when thresholds are crossed.

Geomorphic Process
•The process responsible for the formation and alteration of the earth's
surface.
•The physical and chemical interactions between the earth's surface and
the natural forces acting upon it to produce landforms.
•The processes are determined by such natural environmental variables as
geology, climate, vegetation and base level, to say nothing of human
interference.
Definition:
•The geomorphic processes are all those physical and chemical changes
which effect a modification of the earth’s surgical form
[ Thornbury (1968): Principles of Geomorphology].
•A process by which the earth’s land forms are changed or maintained
[Jim Gardner (1979): Physical Geology].

Fundamentals of Geomorpholgy –Huggett
Figure 1.1 Landforms at different scales and their interactions with exogenic and endogenic

Geomorphic Processes:
 Physical processes which create and modify landforms on the surface
of the earth
 Endogenous (Endogenic) vs.Exogenous (Exogenic) Processes
 Rock Cycle →

Endogenous Processes are large-scale landform building and
transforming processes
– they create relief.
1. Igneous Processes
a. Volcanism: Volcanic eruptions → Volcanoes
b. Plutonism: Igneous intrusions
2. Tectonic Processes (Also called Diastrophism)
a. Folding: anticlines, synclines, mountains
b. Faulting: rift valleys, graben, escarpments
c. Lateral Faulting: strike-slip faults
Earthquakes → evidence of present-day tectonic activity

Also called Gradational Processes, they comprise
degradation and aggradation – they modify relief
→ a continuum of processes – Weathering → Mass Wasting
→ Erosion → Transportation → Deposition
→ these processes are carried through by Geomorphic
Agents: gravity, flowing water (rivers), moving ice
(glaciers), waves and tides (oceans and lakes), wind, plants,
organisms, animals and humans
1. Degradation Processes → Also called Denudation
Processes
a. Weathering , b. Mass Wasting and c. Erosion
and Transportation
2. Aggradation Processes
a. Deposition – fluvial, eolian, glacial, coastal

In geology, the term exhumation refers to the process by which a parcel of
rock approaches Earth's surface. It differs from the related ideas of rock
uplift and surface uplift in that it is explicitly measured relative to the surface
of the Earth, rather than with reference to some absolute reference frame,
such as the Earth's geoid.
Exhumation is almost a synonym for denudation, except some authors have
considered the former to be in the frame of reference of the uplifted rock,
and the latter to be in the frame of reference of the surface towards which
rocks are advected.
Exhumation of rocks occurs either by erosion or by extensional tectonics.
Because the movement of rocks from depth towards the surface cools them,
thermochronometric methods like fission track or radiometric dating strictly
measure exhumation, not rock uplift or erosion rates.[
Outside tectonics, geological exhumation can also describe the return to
Earth's surface of something previously buried in sediments, for example a
landform.

Introduction to Geomorphology

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