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EESA06H3 (560)
Nick Eyles (492)

CHAPTER 11 (2012)

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Environmental Science
Nick Eyles

CHAPTER 11GEOLOGICAL STRUCTURES what causes rocks to bendbreak how they behave when stressed change in bedrock can be caused my powerful forces originating deep within the earth the geologic structures or architecture that results from these tectonic forces can be studied by geoscientistsRecognition of unconformities as well as principle of original horizontality superposition and crosscutting relationshipsimportant structural geology as they are determining relative time structural geology branch of geology concerned with the shape arrangement and interrelationships of bedrock units and the forces that cause them What Causes Rocks to bend and Break Stress and Strain in the Earths Lithosphere tectonic forces move and deform parts of the lithosphere especially along plate margins can cause orientation location shape of rock changes originally horizontal layers can be deformed by tectonic forces that push or compress the layers together until they are shortened by buckling and breaking stress force per unit areawhere stess can be measured it is expressed at a particular point but cant burry stress in rocks that are currently buried when rock bodies are exposed after uplifting and erosion we are able to see their stress strain change in size volume or shape or both in response to stress eg If pizze dough is pushed together or squeezed from both ends then the stress is compressive common along convergent plate boundaries and results in rocks deformed by shortening strain eg An elongated piece of dough will shorten by bending foldingeg A ball of pizza dough may flatten by shortening in the direction parallel to the stress andn elongating in up down direction these 2 types of rock are found along convergent plate boundaries where rocks have been pushed or shoved tensional stress forces pulling away from one another in opposite directions Resuls in a stetching or extension of material If it is rapid it can cause breaking at divergent plate boundaries the lithosphere is undergoing extensionfractures and faults are commonly formed here sheer stress when stresses act parallel to a plane eg Like putting deck of cards in hand and sheering the deck by moving hands in opposite direction shear strain parae to the direction of the stressesthese occur at actively moving faultsHow Do Rocks Behave when stressed elastic rock deformed body recovers its original shape after stress is reducedremovedEg Tensional stress on a rubber bandwhen removed it returns backrocks can only behave in elastic way with VERY LOW STRESSES Once stress applied exceeds the elastic limitrock will break if stetched too far
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