Post on 26-Dec-2015
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.
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 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
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.
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.