Lecturer 2- Geomorphology and Weathering_14

Geomorphology

Goals of the Topic Define geomorphology and identify the fundamental processes shaping the earth’s surface Provide a brief overview of the history of geomorphology Discuss some of the fundamental principles and concepts in geomorphology Definition of Geomorphology Geomorphology is the study of the nature of earth’s landforms and the processes that shape the earth’s surface (Pazzaglia, 2004)

The Focus of Geomorphology Geomorphologists seek to understand why is the earth surface the way it is? (landforms- origin, morphology & evolution/dynamics)

Where do landscape materials come from?

How do landscape materials get down from mountain tops to valley floors or sinks (i.e. lakes/oceans)?

And to predict future changes through a combination of field observations, physical experiments, and numerical modelling.

Why is the earth surface the way it is?

Forces Shaping the Earth’s Surface: Internal (orogenic forces) – tectonic movements & volcanic activities External (exogenic forces) – denudational processes (weathering, mass wasting, glacial, fluvial, wind actions)

Landform & Landscape

•Landform - is an element of the landscape or topography/geomorphological unit characterized by physical attributes such as elevation, slope, orientation, etc. •Examples – hill, valley, sand dunes, mountains etc •A number of factors, ranging from plate tectonics to erosion and deposition, can create and affect landforms •Biological factors can also influence landforms—the role of vegetation in the development of dunes and salt marshes, and the work of corals and algae in the formation of coral reefs.

•It comprises the visible features of an area of land, including the physical elements of landforms such as mountains, hills, and living elements of landcover including indigenous vegetation, human elements including different forms of land use, buildings and structures •An overlay of the physical and cultural elements

Landscape

•Landscapes are a group or aggregate of geomorphic landforms in a given locality •Examples: coastal landscape (caves, geos, arches, stacks, beaches etc)

Historical development of geomorphology

Early contributions to geomorphology

•Leonardo da Vinci (1452- 1519) studied the topography of the Arno River basin, •Drew the first contour map of a whole river basin, and •Believed that rivers carved their valleys and shaped topography.

First Book on Rivers was published by Domenico Gugleilmini in 1697. "The Nature of Rivers“ The book discusses the nature of rivers and their parts, the motion of water, confluents and estuaries, banks, and materials and application.

Italian and French hydraulic engineers developed the study of rivers in the late 17th century to address flooding problems along rivers draining the Alps.

Historical development of geomorphology Cont.

James Hutton Wrote Theory of the Earth in 1795 where he laid the foundation of many of the fundamental principles of Geology. He included chapters on uplift, erosion, and consolidation of rock. Among a group Plutonists who indicated that granite was of igneous origin as oppose to the Neptunists who considered it to be of chemical precipitate (Metamorphism of rocks).


Unfortunately, he did not communicate his ideas very effectively, so they didn’t catch on!

Catastrophism Catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter (Noah’s Flood; and earthquake and volcanic activities) •Nathanael Carpenter (1589–1628) wrote that ‘‘mountains, valleys, and planes were created in the Earth from the beginning, •Such views were echoed by Varenius (1650) and James Ussher that the Creation of Heaven and Earth had occurred ‘‘upon the entrance of the night preceding’’ Sunday, October 23, in the year 4004 BC, with ‘man’ and other creatures appearing on the following Friday.



Uniformitarianism

•Uniformitarianism is the assumption that the same natural laws and processes that operate in the universe now, have always operated in the universe in the past (“the present is the key to the past”) •Uniformitarianism was formulated in the late 18th century, by James Hutton, refined by John Playfair and popularized by Charles Lyell (Principles of Geology in 1830) •Uniformitarianism contrasted catastrophism and consequently did not receive much attention.

John Wesley Powell Early director of USGS who first explored the Grand Canyon and who introduced the idea of base level. Base level: the lowest elevation to which a stream can erode. Usually coincident with sea level.


Grove Karl Gilbert

Powell’s assistant in the Grand Canyon expeditions. He is acknowledged as being the father of modern geomorphology. Gilbert’s was the first to systematically discuss weathering and bedrock erosion (debris production mechanisms) as well as erosion and transport of sediments in the landscape. He also stated the fundamental relations between slope, energy available for erosion, and stream discharge.


Gilbert’s Flume at UC Berkeley

The Transportation of Debris by Running Water (1914)


William Morris Davis : Geographical Cycle (Cycle of Erosion) (1884 -1899)

•rapid/episodic uplift followed by prolonged structural stability during which geomorphic processes, assumed rather than measured, denuded the landscape equated to life forms (youth, maturity, and old age ) •Stage 1 (youthful): Upliftment (high mean elevation, high relief, carving of deep, narrow valleys) •Stage 2 (mature): mean elevation and mean relief steadily decrease, and valleys continue to widen •Stage 3 (old age): valleys can no longer deepen or widen and all landscape lowering is accomplished by the progressive rounding and lowering of interfluves by hillslope creep – (peneplain/peneplanation) •Tectonic uplift or climate change could start the cycle over creating new forms co-existing old ones (polycyclic forms).


http://en.wikipedia.org/wiki/Tectonic_uplift


Geographical Cycle (Cycle of Erosion)

Arid Climate Humid Climate

up

lift ero

sion

Geographical Cycle (Cycle of Erosion)

Critique of Davis’ work: 1) Qualitative nature of the description prevents it from being scientifically tested 2) The idea was misapplied to many landscapes in a predictive sense 3) Variations in lithology will result in differentials in denudational processes etc

Climatic geomorphology

•This is the period when climate was observed to be a major contributing factor in landforms development •Landforms in different parts of the world are directly/indirectly under the control of climate (weathering in humid and arid regions and resultant landforms) •Climatic geomorphology deals with morphosculptures, that is, relief forms that are created primarily by exogenous processes interacting with all other relief-forming factors



Quantitative Geomorphology •Describes landscape evolution by representing geomorphic processes or landscape characteristic as mathematical expressions. •Quantitative geomorphology can involve fluid dynamics and solid mechanics, geomorphometry, laboratory studies, field measurements, theoretical work, and full landscape evolution modelling. These approaches are used to understand weathering and soil formation, sediment transport etc •Most of these models are packaged as computer softwares (e.g. CHILD, GOLEM, CASCADE, CAESAR etc)

Wave propogation model Weathering of limestone

Quantitative Geomorphology


Applied geomorphology •Applied geomorphology - the application of geomorphic theories and principles in addressing environmental issues that are of beneficial to man and the environment. •Applied geomorphology - examines the interactions between human activity and the environment and the resultant effects of these interactions on the biophysical environment.

1. Pazzaglia F. J. (2004). Landscape evolution models. Developments in Quaternary Science, Volume 1 ISSN 1571-0866, DOI:10.1016/S1571-0866(03)01012-1, pp247 – 256.

2. Kusimi, J.M., and Awere-Gyekye, K. (2013). Explanations to the Evolution of Landscapes in Geomorphology; in Selected Readings in Geography: Essays in Commemoration of the 65th Anniversary of the University of Ghana. Edited by George Owusu, Paul W. K. Yankson, Samuel Agyei-Mensah and Emmanuel M. Attua, Woeli Publishing Services.

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Lecturer 2- Geomorphology and Weathering_14

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