Plate Boundaries

Types of Crust• Continental Crust• Less dense granite

• Oceanic Crust• More dense basalt

Divergent Boundaries• Two plates move apart (diverge from each other). • New crust is formed from magma.

• Underwater• Mid ocean ridges.• Seafloor Spreading.• EX: Mid Atlantic Ridge

• On Land• Rift Valleys.• EX: African Rift Valley, New Madrid Fault System

Mid Ocean Ridge

Mid Atlantic Ridge

Rift Valley

Convergent Plate Boundaries• Plates come together (converge)• The denser plate (Oceanic Crust) sinks while the less dense

plate (Continental Crust) rises.• 3 types of collisions….

• Continental colliding with oceanic. • A Zone of Subduction occurs, the denser plate is forced

underneath the less dense plate and melts. • Volcanoes and Trenches.• Possible earthquakes and tsunamis.• EX: Mt. St. Hellens

Oceanic/Continental Convergence

• Oceanic colliding with oceanic.• Subduction • Volcanoes, trenches, and island arcs.• EX: Mariana Trench and Alaskan islands• Possible earthquakes and tsunamis

Oceanic/Oceanic Convergence

• Continental plates colliding with continental plates.• Mountain range• EX: Himalayan Mountains

Continental/Continental Convergence

Transform Boundaries• Two plates move past each other in opposite directions.• Faults lines and earthquakes. • EX: San Andreas Fault

Transform Boundary

Hot Spots• Volcanic activity that does not occur on plate boundaries

occurs at hot spots. • Magma shoots up through the lithosphere. • Hot Spots are in fixed locations, as the lithospheric plates

move over them. • EX Yellow Stone National Park and Hawaii

Tsunami• A series of long waves that travel across the oceans at very

fast speeds.• Caused by Earthquakes which vertically move the sea floor

(zones of subduction).

Geysers and Ocean Vents• A geyser is a vent on Earth’s surface that periodically shoots

out hot water. • An ocean vent is a vent underwater which releases heat,

warming the water around it.• Both are caused by volcanoes!