Changes in the Earth’s Crust

What is stress? You get stressed when you have too much work or have a test to study for You can get stress in certain parts of your body You get stressed when you’re anxious or nervous What kind of stress am I talking about?

Stress Stress is the amount of force per unit area that is applied to something Spaghetti demo

Stress Deformation is when rock changes shape due to stress. Rock layers can bend and eventually break when stress is placed on them. There are 2 types of stress on rocks: 1)Compression 2)Tension

Compression and Tension Compression is the type of stress that occurs when an object is squeezed such as when two tectonic plates collide (converge) Tension is the type of stress that occurs when forces act to stretch an object such as when two tectonic plates separate (diverge)

Folding Occurs when rock layers bend due to stress in the Earth’s crust We assume that rock layers are horizontal so when you see a fold, you know that deformation (change in rock shape) has taken place Folds can be large or small There are 3 different types of folds: 1)Anticline 2)Syncline 3)Monocline

Monocline Rock layers are folded so both ends of the fold are still horizontal

Faulting A fault is the surface along which rocks break and slide past each other The blocks of crust on each side of a fault are called fault blocks There are 3 types of faults: 1)Normal fault 2)Reverse fault 3)Strike-slip fault

Normal fault A normal fault causes the hanging wall to move down relative to the footwall Usually occur when tectonic forces cause tension that pulls rocks apart (diverge)

Reverse fault A reverse fault causes the hanging wall to move up relative to the footwall This is the “reverse” of a normal fault Usually occur when tectonic forces cause compression that pushes rocks together (converge)

Strike-slip fault Occur when opposing forces cause rock to break and move horizontally

Quick check What is the difference between folding and faulting? What is the difference between compression and tension?

Mountain building The 3 most common types of mountains are: 1)Folded mountains 2)Fault-block mountains 3)Volcanic mountains

Folded Mountains Form when rock layers are squeezed together and pushed upward

Fault-block Mountains Form when faulting causes large blocks of the crust to drop down relative to other blocks When the crust is subjected to tension, the rock can break along a series of normal faults

Volcanic Mountains Form when molten rock erupts onto the Earth’s surface Form from new material being added to the Earth’s surface

NO HW! Have a great weekend!