Plate Tectonics

Chapter 1 Section 5

Plates

• What is a plate?• A plate is a piece of the lithosphere• Plates fit closely together along cracks

Plate Tectonics

• The theory of plate tectonics states that pieces of the lithosphere are constantly moving, in very slow motion, due to convection currents.

• The theory includes explanations for how the plates are moved, move, and undergo subduction.

Plate Movement

• When one plate moves, it affects the plates around it– Collide– Pull apart– grind

Convergent

Oceanic – oceanic = subduction (the more dense plate will be the one that is furthest from a ridge because it is cooler and denser)

Continental – continental = mountain range formation or growth

Oceanic – continental = oceanic plate subduction, trench formation, small mountain formation

Divergent

Oceanic – oceanic = sea floor spreading/ocean ridge

Continental - continental = rift valley formation or growth

Transform

Two plates slide past each other

What is the effect of plate movement?

• Volcanos• Mountain ranges• Deep-sea trenches

Types of Plate Boundaries

• Transform Boundaries• Divergent Boundaries• Convergent Boundaries

Transform Boundaries

• Slipping, moving in opposite directions• Earthquakes are common along these

boundaries

Divergent Boundaries

• Two plates move apart, diverge• Common at the mid-ocean ridge (where the

oceanic crust is forms and sea floor spreading occurs)

• Can also occur on land forming a deep valley or rift valley

• Great Rift Valley in east Africa

Convergent Boundary

• Two plates come together, converge• Causes collisions– Can be oceanic - oceanic– Can be oceanic - continental– Can be continental – continental

• The less dense plate will end up on top after the collision– Subduction can occur (two oceanic plates)

Convergent Boundaries

• When two continental crust plates converge, they form mountains because each plate has the same density

Plate Boundaries

• Faults form along plate boundaries– To clarify…• plate boundaries are where pieces of the lithosphere

meet• Faults are breaks in Earth’s crust as a result of the

boundaries and plate movement at the boundaries

Earth’s Crust in Motion

Chapter 2 Section 1

Types of Stress

• Shearing• Tension• Compression

Together, these types of stress change the shape and volume of rock.

This change in volume or shape is called deformation.

Types of Stress

TensionThe stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle. The effect of tension on rock is somewhat like pulling apart a piece of warm bubble gum. Tension occurs where two plates are moving apart.

Types of Stress

CompressionThe stress force called compression squeezes rock until it folds or breaks. One plate pushing against another can compress rock like a giant trash compactor.

Types of Stress

ShearingStress that pushes a mass of rock in two opposite directions is called shearing. Shearing can cause rock to break and slip apart or to change its shape.

Faults

1. When enough stress builds up in rock, the rock breaks, creating a fault.

2. A fault is a break in the rock of the crust where rock surfaces slip past each other.

3. The rocks on both sides of a fault can move up or down or sideways.

4. Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks.

Specific Types of Faults

• Strike-slip faults• Normal Faults• Reverse Faults

Strike-slip Fault

• The plates slip past each other sideways

• Little up-or-down movement

• Transform boundary• San Andreas Fault in

California

Normal Faults

• Fault is at an angle• Have a footwall and a

hanging wall• The hanging wall slips

downward• Rio Grande Rift valley

in New Mexico

Reverse Faults

• The hanging wall slips up, over the footwall

• Appalachian Mountains

• Peaks at Glacier National Park in Montana

Changing Earth’s Surface

1. The forces produced by the movement of Earth’s plates can fold, stretch, and uplift the crust.

2. Over millions of years, the forces of plate movement can change a flat plain into landforms such as:

1. anticlines and synclines2. folded mountains3. fault-block mountains4. plateaus

Fault-Block Mountains As tension forces pull the crust apart, two parallel normal faults can form a range of fault-block mountains, like the Beaverhead Range in Idaho.