Sharon Johnson GeoImages.Berkeley.EDU

Sharon Johnson http://GeoImages.Berkeley.EDU.

Folding, Faulting and Denudation


Forces in Balance

Some forces build up the earth – e.g. plate tectonics, volcanoes and folding and faulting.

Other forces tear down that which is built – e.g. rivers, glaciers and weathering



This unit will examine the “balance” between some localized forces – folding, faulting and denudation (levelling of the surface)



Tectonic activity is an “earth-building” activity

http://www.geog.ouc.bc.ca/physgeog/contents/10l.html


Folding is the process that bends and twists rocks, usually due to compression

Faulting is the process where rocks move past each other along a fracture

http://volcano.und.nodak.edu/vwdocs/volc_images/

img_arenal1.html


Volcanism is the term used to describe the movement of molten

rock beneath or above the earth’s surface (covered in another

unit)


Folds

Occur when compressional forces cause rock layers to bend


Anticline – upfolds or ridges


Syncline – downfolds or valleys

http://astro.sau.edu/~earth/html/md11.html

Folding


Faults

This is a transform plate boundaries, the most

famous example of which is the San Andreas Fault


Folding, Faulting and DenudationOn a smaller scale there are a number of other types of faults, categorized by the relative motion of the blocks of

earth:

http://salem.k12.va.us/shs/lester/ch16faulting.html


Normal fault – side or profile view



Reverse fault – side or profile view



Strike-slip fault – side and top view


Folding, Faulting and DenudationWhere a block of earth rides up or down between two

parallel fractures we see grabens and horsts


Denudation – processes which tend to level the earth’s surface.

Consists of two broad categories :

•degradation (weathering, erosion and transportation)

•aggradation (deposition)

Lisa Wells http://geogweb.berkeley.edu/GeoIma

ges/Wells/geomorph/adobe.html

Folding, Faulting and DenudationOnce new landforms are created by tectonic forces,

weathering and erosion begin to wear away at those forms. The overall effect is a “softening” of landscapes.

Lisa Wells http://geogweb.berkeley.edu/GeoIma

ges/Wells/geomorph/tufoni1.html


Occasionally, differential erosion creates some interesting features


Chemical weathering involves a chemical change in at least some of the minerals within a rock.

Mechanical weathering involves physically breaking rocks into fragments without changing the chemical make-up of the minerals within it.

http://www.geo.duke.edu/geo41/wea017.gif


Mechanical weathering

http://www.dc.peachnet.edu/~pgore/geology/geo101/weather.htm


Chemical weathering

Karst topography


As soon as a rock particle (loosened by one of the two weathering processes) moves, we call it erosion or mass wasting. Mass wasting is simply movement down slope due to gravity. Rock falls, slumps, and debris flows are all examples of mass wasting. We call it erosion if the rock particle is moved by some flowing agent such as air, water or ice.

http://maps.unomaha.edu/maher/geo117/part2/masswastingpics/

Svalbardtalus.jpeg


Talus slope at base of mountain

www.ahs.cqu.edu.au/humanities/geography/52120/trial2/

folding&.htm


Consider this famous landform feature resulting from a resistant layer of rock appearing at the surface, surrounded

by softer rocks. (Ayers Rock)

http://www.northernterritory.com/3-2.html


http://www4.vc-net.ne.jp/~klivo/gen/geology.htm

Folding, Faulting and DenudationIn Ontario, the Niagara Escarpment has been formed by

differential erosion.



http://www4.vc-net.ne.jp/~klivo/gen/nmapeng.gif


The escarpment is the exposed edge of a large scale syncline (geosyncline).



The escarpment is the exposed edge of a large scale syncline (geosyncline).


Where rivers cross the escarpment, waterfalls may be formed by undercutting.


Some of these waterfalls are quite spectacular.

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Sharon Johnson GeoImages.Berkeley.EDU