lecturer 2- geomorphology and weathering

Geomorphology

Goals of the Topic Define geomorphology and identify the fundamental processes shaping the earths 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 earths landforms and the processes that shape the earths 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 Earths Surface: Internal (orogenic forces) tectonic movements & volcanic activites External (exogenic forces) denudational process (weathering, mass wasting, glacial, fluvial, wind)

Landform & Landscape

Landform - is 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 generate and affect landforms Biological factors can also influence landformsthe 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

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 didnt catch on!


Catatrophism Catastrophism is the theory theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter (Noahs Flood; and earthquake and volcanic activities) Nathanael Carpenter (15891628) 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

Powells assistant in the Grand Canyon expeditions. He is acknowledged as being the father of modern geomorphology. Gilberts was the first work 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.


Gilberts 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).



Geographical Cycle (Cycle of Erosion)

Arid Climate Humid Climate

up

lift

erosio

n

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 weatherin 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.

Why is the earth surface the way it is?

Where do landscape materials come from?

Weathering The physical disintegration and chemical decomposition of minerals rocks insitu

Factors Influecing weathering Geologic Factors Rock Type: different minerals have rates of weathering

1st to crystallise

last to crystallise

Bowens Reaction Series

Goldrich Stability Series

Slow Weathering

Fast Weathering

Why is sand so prevalent at Earths surface?

It is composed of quartz, a relatively stable mineral!

Mean Lifetime of a 1mm crystal at surface (in years) Quartz 34,000,000 Kaolinite 6,000,000 Muscovite 2,600,000 Microcline (Alk. Feldspar) 921,000 Albite (Sodium Plagioclase) 575,000 Sandine (Alk. Feldspar) 291,000 Enstatite (Pyroxene) 10,100 Diopside (Pyroxene) 6,800 Forsterite (Olivine) 2,300 Nepheline (Amphibole) 211 Anorthite (Calcium Plagioclase) 112

Rock Type

Weathering

Factors Influecing weathering Cont. Geologic Factors

Rock fissility: cracks, joints, fractures facilitate the penetration of weathering agents. Hardness/softness is also critical in weathering

Rock texture: degree of fine or coarse nature of grains size of rocks (affects permeability of weathering agents)

Weathering

Factors Influecing weathering Cont.

Climatic Conditions temperature and precipitation. Temperature increases the rate of chemical process, precipitation increases the availability of weathering reagents, acids) Biotic Factors vegetative cover (humid acids ect), rodents and man Geomorphic Factors slope ( deep chemical weathering is favoured on gentle slopes & vice versa)

lecturer 2- geomorphology and weathering

Documents

geomorphology leonardo

history of geomorphology

geomorphology goals

nature of rivers

physical elements of

study of rivers

nature of earths landforms

earths surface pazzaglia