Plate Boundaries

3 Main Types: –1. Divergent Boundaries Plates moving AWAY from each other –2. Convergent Boundaries Plates moving TOWARD each other Three Main Types: –Oceanic to Continental –Oceanic to Oceanic –Continental to Continental –3. Transform Boundaries Plates slide past each other

Divergent Boundary

Divergent Boundaries Where plates are moving away from one another. Characteristics: –Lengthening –Thinning of Lithosphere –Shallow Earthquakes –Fissure Volcanoes –Rift Valleys Locations: –Oceanic Ridges –Mid-Atlantic Ridge –East-African Rift –Formation of Basalt Results in: –Sea floor spreading

Divergent Boundary Oceanic – Occurs above rising convection currents that lift up the plate – The plate travels in direction of flow. – The plate is stretched thin, breaks and pulls apart. – The magma flows into the fissure, solidifies and the process repeats itself. Continental: – Two plates pull apart, faults develop on both sides of the rift; the central blocks slide downwards. – Earthquakes occur. – Streams and rivers flow into the rift and form a lake.

Convergent Boundary Continental/Oceanic

Convergent: Continental to Oceanic As they collide, the less dense continental plate overrides the oceanic plate. – Oceanic plate is forced down; temperature increases; plate becomes magma in convection current Subduction Zone: –Where less dense crust slides under the more dense crust –Location of Volcanoes and Seafloor Trenches Characteristics: –Coastal Mountain Ranges –Continental Volcanic Arcs Andes, Cascades –Formation of Volcanic Island Arcs Japan, Philippines

Andes Mountains, South America

Convergent Boundary Oceanic/Oceanic

Convergent: Oceanic to Oceanic Two oceanic plates collide. – The older (most dense) plate will subduct beneath the younger plate. Subduction Zone Results in: – Trenches – Island Arcs – Chain of Volcanic Isands – Deeper Earthquakes Examples: –Japan –The Caribbean Island s

Convergent Boundary Continental/Continental

Convergent: Continental to Continental Two thick continental plates collide – Both have a density that is much lower than the mantle, which prevents subduction. Example: – Himalaya Mountain Range – Alps

Transform Fault Boundaries Boundary between two plates that are sliding past each other Earthquakes appear along fault lines Example: – San Andreas Fault

San Andreas Fault, CA

Questions... What are the three types of boundaries? What direction do plates go for each? Which boundary has a subduction zone…what occurs at a subduction zone?

C. Why do the plates move? 1.Due to tremendous heat, rock in the asthenosphere is like hot taffy 2.This allows plates to ride on top of hot, flowing rock. 3. Plates move because heat is being released from deep inside the earth. 4. Convection currents causes hot material to rise and expand (plates diverge) and cooler material to sink and contract (plates converge).

Questions... What causes plates to move? How is a convection current formed?