3Horizontal movements of the Earth’s Crust Takes place from compression and tensional forcesTension – stress tending to pull rock masses apartCompression – Stress tending to squeeze rock masses togetherResponsible for formation of fold mountains.As a result of compressional forces acting in 2 opposite directions, the crustal rocks bend and form a series of arches & troughs.This is known as folding of crustal rocks that usually occur in a zone where the crust is weak.The lines of fracture are known as faultsBoth Processes are result in mountain building
4What is a Fold?A fold is a bend in rock strata resulting from compression of an area of the Earth’s crust .The severity of compression is indicated by the tightness of the folds.Since the compressional force is acting towards the centre, the intervening land rises up in a series of folds
5Types of Folds: Anticline An anticline is a convex up fold in rock that resembles an arch like structure with the rock beds (or limbs) dipping way from the center of the structureNote how the rock layers dip away from the center of the fold are roughly symmetrical.
6Types of Folds: Syncline A syncline is a fold where the rock layers are warped downwardBoth anticlines and synclines are the result of compressional stressNote how the rock layers dip toward the center of the fold and are roughly symmetrical
7Synclinal folds in bedrock, near Saint-Godard-de-Lejeune, Canada
8More Complex types of Folds More complex fold types can develop in situations where lateral pressures become greater. The greater pressure results in anticlines and synclines that are inclined and asymmetrical
9Recumbent FoldA recumbent fold develops if the center of the fold moves from being once vertical to a horizontal positioncommonly found in the core of mountain ranges and indicate that compression and/or shear forces were stronger in one direction
10Overthrust FaultExtreme stress and pressure can sometimes cause the rocks to shear along a plane of weakness creating a fault. We call the combination of a fault and a fold in a rock an overthrust fault
11Fold MountainsThe compressional force exerted on the crust is a result of movement of earth’s plates.When the plates converge, the weak rocks and sediments lying between the 2 plates get squeezed and get folded.Parallel folds give rise to long chains of parallel mountain ranges with high peaks.The up-folds form fold mountains while the down folds form longitudinal valleys.
17FaultingFaults are large scale internal movements causing large scale physical features especially mountains and valleysIf the force is moderate only cracks may appear in the rocks.The displacement that occurs results in formation of faults.Such fractures are divided into Joints & Faults.A joint is a fracture where a rock seems to be joined together without any movementit may become a fault when displacement takes place
18Location of some of the major faults on the Earth. Where do you notice that a majority of the faults in the world occur?
19Normal FaultNormal faults occur when tensional forces act in opposite directions and cause one slab of the rock to be displaced up and the other slab down
20Reverse Fault Reverse faults develop when compressional forces exist Compression causes one block to be pushed up and over the other block.
21Graben FaultA graben fault is produced when tensional stresses result in the subsidence of a block of rock. On a large scale these features are known as Rift Valleys
22Rift Valleys (AKA Graben) Major relief feature of Faulting Activity is Rift Valley.A Rift Valley may be formed in two ways :(1) When the middle portion between two normal faults is dropped downward the sides remain stable.(2) When the middle portion remains stable and the two sides are raised upwardThese valleys have flat bottoms and steep sides
23Example: Great Rift Valley, Africa Why is this important?Because the rapidly eroding highlands have filled the valley with sediments, a favorable environment for the preservation of remains has been created. The bones of several hominids ancestors of modern humans have been found there, including those of "Lucy“
24Ottawa-Bonnechere Graben The Ottawa-Bonnechere Graben (also known as the Ottawa Graben), with its branch the Timiskaming Graben, is an ancient rift valley in the Canadian Shield of Northeastern Ontario and Quebec, CanadaThis rift valley was formed when the Earth's crust moved downward about a kilometre between two major fault zones known as the Mattawa and Petawawa faultsThese ancient faults are still active and occasionally release stress in the form of earthquakes, such as the 1935 Timiskaming earthquake and the 2000 Kipawa earthquake.The length of the graben is about 700 km (435 mi)Runs from the Montreal area on the east to near Sudbury and Lake Nipissing on the west
29Fault-Block Mountains Block mountains are another important feature of Faulting caused by the Tensional features in the Earth’s crustThe mechanism of formation of Block mountains is same as the Rift valleyThe Block mountains are often found on the sides of the Rift valleyIt is because the land between two parallel faults is either subsides to form a Rift valley or rises to form Block mountains
30Strike-Slip (transform) Fault The final major type of fault is the strike-slip or transform fault. These faults are vertical in nature and are produced where the stresses are exerted parallel to each otherA well-known example of this type of fault is the San Andreas fault in California.
31Challenge With the Fault Models can you demonstrate: A normal fault? A reverse fault?A graben fault?A horst fault?