Rocks Under Stress_1

Rocks Under Stress_1

1. stress and strain

   • stress is the amount of force applied to the rock
     • types of stress
       • tensional stress is where to sides of a rock are being pulled apart
       • compressional stress is where opposite sides of the rock are squashed together.
       • confining stress is where stress is equal from all angles
       • shear stress is where the top is forced one way, the bottom is forced the other.
   • strain is the change in the rock
     • types of strain
       • plastic
         • heat is usually involved, so the rocks shape is easily changed. this is like plasticine.
       • elastic
         • the rock bends like in plastic, but returns back to its original shape when the stress is stopped, like an elastic band
       • brittle
         • no heat involved so the rock snaps like a biscuit

2. faults and folds

   • faults
     • normal faults
       • the walls are pulled away from each other and one sinks below the other, leaving a slope.
     • reverse faults
       • the two sides are pushed together, one rides up over the other creating a hanging wall
     • strike slip faults
       • the two sides are pushed in opposite horizontal directions, so they slide past each other
   • folds
     • anticline- the rock folds up like an 'A'
     • syncline- the rock folds down like a 'sink'
     • overfold- the fold has lots of force at one side so it is folde over to one side

3. by Oliver Russell 10E