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Introduction to Geomorphology

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Geologic time scale, Uniformitarianism, Catastrophic concept, Geomorphic process-agent cause and product, Hutton's concept, Davis Concept, Darwin's concept, Gilbert's concept

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Introduction to Geomorphology

  1. 1. Introduction to Geomorphology Prof. P. K. Mani ACSS-751 BCKV, WB, India
  2. 2. What is the Geologic Time Scale?What is the Geologic Time Scale?
  3. 3. 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
  4. 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
  5. 5. 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
  6. 6. 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
  7. 7. 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)
  8. 8. 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.
  9. 9. 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.
  10. 10.  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.
  11. 11. 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.
  12. 12. 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)
  13. 13. 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
  14. 14. Catastrophic TheoriesCatastrophic Theories • Georges Cuvier: Great catastrophic floods produced unconformities, and carved Earth’s landscape.
  15. 15. 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.
  16. 16. -- 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
  17. 17. 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).
  18. 18. 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.
  19. 19. 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
  20. 20. 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.
  21. 21. 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
  22. 22. 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.
  23. 23. Mount St. Helen’s Before After Catastrophism vs. Uniformitarianism Lyell
  24. 24. Paradigms (1 of 2)
  25. 25. Davis' Landscape evolution model An example from an arid climate. Davis' idea of a Peneplain ‘‘Davis' Cycle of erosion
  26. 26. 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
  27. 27. 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
  28. 28. 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
  29. 29. • 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.
  30. 30. Time = 1 Time = 0 Time = 2
  31. 31. 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.
  32. 32. 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
  33. 33. 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.
  34. 34. 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].
  35. 35. Fundamentals of Geomorpholgy –Huggett Figure 1.1 Landforms at different scales and their interactions with exogenic and endogenic
  36. 36. Geomorphic Processes:  Physical processes which create and modify landforms on the surface of the earth  Endogenous (Endogenic) vs.Exogenous (Exogenic) Processes  Rock Cycle →
  37. 37. Exogenic / Endogenic Systems
  38. 38. 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
  39. 39. 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
  40. 40. 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.

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