Earthquakes, Volcanoes, and Mountain Building

Tectonic Plate Boundaries

• Convergent: Tectonic plates collide

• Divergent: Tectonic plates move away from one another

• Transform: Tectonic plates slide past each other horizontally

Mountain Building• Mountains are

landmasses that rise well above Earth’s surface.

• Mountains form at convergent boundaries. – Two continental

plates of equal densities collide and push up the land• Earth’s crust folds

and breaks as a result

Earthquakes• Earthquakes are

the shaking movement of Earth’s surface.

• Earthquakes occur at transform boundaries. – The boundaries of

two plates move against each other

– Pressure is built up, causing a violent shift• This movement

causes an earthquake.

Volcanoes• Volcanoes are mountains that form

when magma is forced to Earth’s surface

• Volcanoes form at convergent boundaries, divergent boundaries, and hot spots.

Volcanoes at Convergent Boundaries

• When two plates collide, the denser one subducts beneath the less dense one.– The denser plate

that goes under melts and forms magma• This magma can be

forced through vents to form volcanic mountains.

Volcanoes at Convergent Boundaries

Example: Mount Etna, Ring of Fire volcanoes

Volcanoes at Divergent Boundaries• Two plates beneath the ocean can

move apart– A vent is exposed and magma slowly

rises to the surface• New oceanic lithosphere is formed

• This process is called sea-floor spreading

Volcanoes at Divergent Boundaries

Example: Iceland’s volcanic islands

Volcanoes at Hot Spots • A hot spot is a

place beneath the earth where very hot magma exists.–When a plate

moves over a hot spot in the mantle, a vent can be exposed• Fountains of

magma punch through the crust

Volcanoes at Hot Spots

Example: The Hawaiian Islands