Folding and FaultingFolding and FaultingBy Gulbahar JamaliBy Gulbahar JamaliContact: 03023076659Contact: 03023076659Email: Gulbaharjamali@gmail.comEmail: Gulbaharjamali@gmail.comUniveristy of SindhUniveristy of Sindh
FoldsFolds• A fold is when the earth’s crust is pushed up from its sides. Thereare six types of folds that may occur:• Anticline• Syncline• Tight Fold• Overfold• Recumbent Fold• Nappe Fold
AnticlineAnticline• An anticline occurs when atectonic plate is compressed bymovement of other plates. Thiscauses the center of thecompressed plate to bend in anupwards motion.• Fold mountains are formed whenthe crust is pushed up as tectonicplates collide. When formed,these mountains are usuallyenormous like the newly formedRocky Mountains in WesternCanada and the United States• To the top right is a picture of ananticline. Beneath is a picture ofthe Rocky Mountains.
SynclineSyncline• A syncline is similar to ananticline, in that it is formed bythe compression of a tectonicplate. However, a synclineoccurs when the plate bends ina downward motion.• The lowest part of the synclineis known as the trough.• To the top right is a diagram ofa syncline fold (The bottom ofthe fold center is the trough).Beneath, is an example of asyncline in California. Can youdistinguish the trough in thispicture?
Tight FoldTight Fold• A tight fold is a sharp peakedanticline or syncline.• It is just a regular anticline orsyncline, but was compressedwith a greater force causingthe angle to be much smaller.• Folds such as these occur toform steep mountain slopeslike those in Whistler, BritishColumbia.• To the left is a photo of a tightfold formed by extremepressure on these rocks.
OverfoldOverfold• An overfold takes place when folding rock becomes bentor warped.• Sometimes the folds can become so disfigured that theymay even overlap each other.• An example of overfolding is shown in the diagrambelow.
Recumbent FoldRecumbent Fold• This type of fold iscompressed so much thatit is no longer vertical.• There is a large extent ofoverlapping and it cantake the form of an “s”.• To the right is a diagramthat shows the process ofrecumbent folding.
Nappe FoldingNappe Folding• This fold is similar to arecumbent fold becauseof the extent of foldingand overlapping.However, nappe foldingbecomes so overturnedthat rock layers becomefractured.• To the right is a picture ofsomeone standing undera fractured fold.
FaultsFaults• A fault is when tension and compression associated with plate movementis so great that blocks of rock fracture or break apart. This process canoccur very rapidly, in the form of earthquakes. The damage caused bythis event can be very destructive and cause severe changes to theearths surface. There are five types of faults that can occur:• Normal Fault• Reverse Fault• Tear Fault• Rift Valley• Horst Fault
Normal FaultNormal Fault• This occurs when rocks moveaway from each other due tothe land moving apart.• When the rocks move apart,the side with the less stabletectonic plate drops below theside with the more stable plate.• On the top right is themovement of a normal fault. Apicture is also shown below.Notice the displacement of thedifferent types of rock on eachside of the fault.
Reverse FaultReverse Fault• Reverse faults are the opposite ofnormal faults. Rocks arecompressed such that one platemoves up while the otherdescends below it.• When plates compress and crack,usually the more dense one isforced under the less dense one.This is similar to the action of thecontinental crust colliding with theoceanic crust. Here the moredense crust, being the oceaniccrust is forced under thecontinental crust.• To the right is an animation of areverse fault. Below that is a realpicture of what a reverse faultlooks like.
Tear FaultTear Fault• A tear fault, also known as a transform fault, occurs when twotectonic plates slide in a lateral motion past each other.• This type of fault causes the most severe earthquakes because theygrind against each other. These earthquakes can either be shallowor deep and cause tremors over a short or long period of time.• Tear faults can occur frequently, especially along the coast ofCalifornia.
Rift ValleyRift Valley• A rift valley is when two normalfaults occur parallel to eachother and the land sinksbetween the faults.• There are two major examplesof this. One being the GreatRift Valley in North Africa andthe other, the San AndreasFault in California.• The top right picture is SanAndreas Fault and on thebottom right is a diagram ofwhat a rift valley looks like.
Horst FaultHorst Fault• A Horst is the opposite ofa rift valley. The landbetween the parallelfaults is forced upwardbecause the two faultsare being pushedtogether.• This process can take along time to occurbecause the averageplate movement is oneinch per year.• There are examples ofhorst faults on the left.
SummarySummary• Folding and faulting has a major influenceon the way the earth looks. Mountainsform and disappear over time, as well aslarge rift valleys and other features. Thishas an impact on where and how we live.