Stress in the earth’s crust

Stress in the Earths Crust

Stress in the Earths CrustBy: Egee F. Firmalo

ObjectivesList different types of tresses that cause different type of deformationCompare the different types of folds and the conditions under which they form.Compare fractures and faults and define how are they related to earthquakes.Compare how mountains form and at what types of plate boundaries.

What causes rocks deformation?Rocks are solid, but will respond when force are applied to them. When rock deformation is being discussed the term stress is used rather than pressure.

The response may involve tiny changes in the volume and shape of the rock, including slow flow. Such changes are called deformation.

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What is a stress?Stressis the force applied to a rock.In Geology stress is the force per unit area that is placed on a rock.

Types of StressConfining stressCompressionstressTensionstressShearstress

Confining stressConfining stresshappens as weight of all the overlying rock pushes down on a deeply buried rock. The rock is being pushed in from all sides, which compresses it.

The rock will not deform because there is no place for it to move.

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CompressionstressCompressionstress squeezes rocks together.Compression causes rocks to fold or fracture. Compression is the most common stress at convergent plate boundaries.

Tensionstress

Tensionstress pulls rocks apart.Tension causes rocks to lengthen or break apart.Tension is the major type of stress found at divergent plate boundaries.

ShearstressShearstress happens when forces slide past each other in opposite directions. This is the mostcommon stress found at transform plate boundaries.

Compression Stress

Tension Stress

Shear Stress

FoldsWhen rocks are experiencing stress deform plastically, the rock crumple into folds.When a rock bends without breaking, it folds..Folds are made up when two plates the earths crust collide.

A fold is a rock formation that has been made by flat rocks that has been deformed through the stress. 16

three types of foldsMonoclinesAnticlines Synclines

monoclineA monoclineis a simple one step bend in the rock layers.In a monocline, the oldest rocks are still at the bottom and the youngest are at the top.

anticlineAnanticlineis a fold that arches upward.The rocks dip away from the center of the fold.The oldest rocks are found at the center of an anticline. The youngest rocks are draped over them at the top of the structure.

When upward folding rocks form a circular structure, that structure is called adome. If the top of the dome is eroded off, the oldest rocks are exposed at the center.

synclineAsynclineis a fold that bends downward.In a syncline, the youngest rocks are at the center. The oldest rocks are at the outside edges. When rocks bend downward in a circular structure, it is called abasin.

FractureFractures are among the most common of all geologic features.A crack or a fault in a rock.

Faults

The place where movement occurs along plate boundary.Faults are fractures in Earth's crust where rocks on either side of the crack have slid past each other.Fault are cracks in earths crust where movement occurs on at least one side .

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Parts of a faultHanging WallFoot wall

Types of FaultNormal faultReverse FaultStrike Slip Faults

Normal faultNormal fault create space.Two blocks of crust pull apart, stretching the crust into a valley.

Places like west of Rocky mountains are affected by normal faults like south Oregon, and southwestern Idaho, eastern California. Western euthah, and the entire of state of neveda. The Basin and Range Province in North America and the East African Rift Zone are two well-known regions where normal faults are spreading apart Earth's crust.31

Reverse faultsReverse faults, also called thrust faults, slide one block of crust on top of another.These faults are commonly found in collisions zones, where tectonic plates push up mountain ranges such as the Himalayas and the Rocky Mountains.

Canadian Rockies, rocky mountain, Appalachian mountains, are types of mountain created by reverse faults.32

Strike-slip faultsStrike-slip faults indicate rocks are sliding past each other horizontally, with little to no vertical movement. Both the San Andreas and Anatolian Faults are strike-slip.

MountainsMountains are magnificent and inspiring features. Just thinking of mountains conjures up beautiful images of places like the Rockies, the Andes, Hawaii and the Alps. But not all mountains are the same. Though they all take a very long time to form, mountains are created in different ways depending on where they are on Earth. Some mountains are created by land pushing together, while others are formed over hotspots on Earth.

Let's take a closer look at the mountain building process to better understand how these incredible structures come to be.

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Tectonic Plates

The earth is like a puzzle, and all the pieces that make up this puzzle is called tectonic plates,36

Plate BoundariesAs plates interact, a boundary between these plates exist or locations where two tectonic plates meet.

As tectonic plates of the earth or giant piece of the earth crust move and crash into each other. Plate boundaries are formed.37

Three types of plate boundariesDivergent boundaryConvergent boundaryTransform plate boundary

Divergent BoundaryAdivergent boundaryoccurs when two tectonic plates move away from each other. This most often takes place at ocean ridges.Volcanic activity is the most common seen in a divergent boundaryAs the plates separate from each other new crust is being made.

This type of plate boundary is caused by a tension stress and then will causes a fault. As the plates separates from each other volcanic activity is one of the most common result but this happens when a divergent boundary is in the ocean floor.39

African rift valley

If divergent boundary occurs in the land or in the continent a rift valley is a result. And African rift valley is one of the example.40

Convergent BoundaryWhen two plates come together, it is known as aconvergent boundary.Convergent plate boundaries are locations where lithospheric plates are moving towards one another. The impact of the two colliding plates buckles the edge of one or both plates up into a rugged mountain range, and sometimes bends the other down into a deep seafloor trench.

Convergent boundary is caused by compression stress. Remember in divergent boundary new crust is being made by the splitting of a tectonic plate. But in convergent boundary is two tectonic plates are being joined together forming a new crust. Through the compression stress two plates are being pushed to each other to become one and in this type of boundary is were mountains builds up.The plate collisions that occur in these areas can produce earthquakes, volcanic activity and crustal deformation. 41

As plates collide to each other they will form high mountain ranges like the Himalayas mountain.42

Transform plate boundariesTwo plates sliding past each other forms atransform plate boundary.A boundary were plates are slide past each other.At this type of boundary the only effect is the earth quake.

Another way of plates can interact is by sliding past each other and this result in a transform plate boundary. Tectonic plates are grinding past each other as they move in opposite direction.43

The most famous example of transform boundary is the San Andreas fault in California. The fault is the edges of pacific plate and the North American plate. The pacific plate is moving northwest at the rate of several centimeters per year. At this type of boundary the only effect is the earth quake.44

Plate BoundariesType of StressKind of DeformationTypes of that deformationExampleDivergent BoundaryTensional StressFractureFault (normal fault)West Africa rift ValleyConvergent BoundaryCompressional StressFoldFracture(It can be any type of fold)Fault (Reverse Fault)Himalayan MountainAndes MountainTransform plate boundariesShear stressFractureFault (Strike Slip Fault)San Andreas Fault

By Henry David ThoreauYou must love the crust of the earth on which you dwell more than the sweet crust of any bread or cake. You must be able to extract nutriment out of a sand-heap. You must have so good an appetite as this, else you will live in vain.

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The following videos are one of my references it is not included in the presentation.48

Thank you for looking. Hope this presentation is helpful52