Mountain Building Lesson 4.7 How are mountains formed? Lesson 4.7

Stressed Out The movement of tectonic plates places stress on rocks Deformation- processes by which rock changes shape under stress – Rocks can bend under stress, but if the stress is too large or happens quickly, it can break – When rock bends, folds forms – When rocks break, faults form

Types of Folds Folding occurs when rock layers bend under stress – Will appear bent or buckled Scientists assume rocks start out as horizontal layers deposited in top of each other – When they see a fold, they know deformation has occurred – Two common types of folds Synclines Anticlines

Types of Folds Syncline- look like rocks layers that are arched upwards, like a bowl Anticlines-Layers are high in the middle and are arched downward. – Often, both types will be visible in the same rock layers.

Types of Faults The crack that forms when large blocks of rocks break and move past each other is called a fault. – Fault blocks: blocks on either side of fault – The sudden movement of fault blocks can cause earthquakes There are 3 main kinds of faults – Classified bases on the way the faults blocks move Strike-slip faults Normal faults Reverse faults

Strike-Slip Fault Fault blocks move past each other horizontally. – Shear stress causes rocks to be pushed in parallel but opposite directions Release of energy can cause earthquakes – Are common along transform boundaries San Andreas fault system in California is an example of a strike-slip fault

San Andreas Fault

Normal Fault Hanging wall moves down relative to the footwall – Called normal because they move in a way you would normally expect as a result of gravity – From when rock is under tension A stress that stretches or pulls rock apart Common along divergent boundaries – Basin and Range area in the US is an example of a location with normal faults.

Basin and Range Area

Reverse Fault Hanging wall moves up relative to the footwall – Reverse of what you would expect as a result of gravity – Form from the result of compression Stress that squeezes or pushes rock together Common along convergent boundaries – San Gabriel Mountains are an example is the US

San Gabriel Mountains

Types of Mountains Mountain can form from folding, volcanism, and faulting – Uplift, a process that can cause land to rise can also contribute to mountain building – Tectonic plates are always in motion, some mountain are constantly being uplifted 3 types – Folded Mountains – Volcanic Mountains – Fault-Block Mountains

Folded Mountains Layers are squeezed together and pushed upwards Form at convergent boundaries Examples: – Appalachian Mountains – Pyrenees

Volcanic Mountains Form when melted rocks erupts onto Earth’s Surface – Many located at convergent boundaries – Volcanoes on the ocean floor can grow so tall that they rise above the surface of the ocean, forming islands – Ex: Mt. Griggs

Fault-Block Mountains Form when tensions makes the lithosphere break into many normal faults – Pieces of the lithosphere drop down – Example: Teton Mountains and Sierra Nevada