Plate Boundaries

Why Plates move: •Convection!!!

Types of Plate Boundaries• Convergent Boundaries: • Oceanic Crust subducts under Continental Crust• Oceanic Crust subducts under Oceanic Crust• Continental Crust collides with Continental Crust

• Divergent Boundaries

• Transform Boundaries

Oceanic Crust Subducts under Continental Crust• What’s happening: • Plates are coming together.• The denser, heavier oceanic plate is subducting underneath the less dense continental crust.

• Characteristics: • Volcanoes form inland from continental coastline.• Composite Cone Volcano and Cinder Cone eruptions. Very

explosive and dangerous. • Deep Earthquake activity• Trench at the Subduction area.

• Example: Cascade Mountain range on West Coast of US

Oceanic Crust Subducts under Oceanic Crust• What’s Happening:• Plates are coming together• One oceanic plate subducts under the other

• Characteristics• Trenches at the subduction area• Earthquake activity• Shield Volcano eruptions

• Example: Japan

Continental Crust Collides with Continental Crust• What’s happening:• Plates are coming together• No subduction! The two plates collide, the crust buckles,

raising the elevation of the surrounding areas. • Characteristics• Mountains, not volcanic• Some earthquake activity

• Example: • Himalayan Mountains

Example of Continental Convergence

Divergent Boundaries• What is happening: • Plates are spreading apart• Typically found in oceanic

crust• Characteristics:• Long crack in the crust,

offset by a series of transform faults on both sides of the rift• Basaltic eruptions• Submarine mountain

chain on the ocean floor• Shallow Earthquakes

Transform Faults• What’s happening: • Plates are sliding horizontally past each other as the two plates move in opposite directions

• Characteristics: • Earthquakes! Plates may lock then suddenly move resulting in major earthquake activity• No volcanic activity

Hotspots- No interaction between two plates• What’s happening: • Hot spot activity occurs within one single plate due to unusually high temperatures in the mantle at that location. • The plate moves over a stationary mantle hot spot•Most common under oceanic crust except for Yellowstone National Park

Hot spots• Characteristic Features: • Chain of volcanoes forms as the plate continues to move over the hot spot• Shield Volcanoes• Quiet eruptions

• Submarine seamounts, volcanoes in the chain that never reached sea level are common on the ocean floor

Pop Quiz: 1. Name the three major types of plate boundaries2. Describe the main characteristics of each: 3. What type of boundary would I need to be at to find volcanoes?4. What type of boundary would I find in the middle of the Atlantic Ocean? 5. What is formed from a hot spot?