Types of plate boundaries Divergent boundary Where two plates move apart from each other Convergent boundary Where plates push into each other Transform boundary Where plates scrape past each other

Sea Floor Spreading Spreading Center Another name for a divergent boundary in the sea floor What can form here Rift Valley Gap between mid-ocean ridges Mid-ocean ridges Longest chains of mountains in the world Mid-Atlantic Ridge – Runs from Iceland to Antarctica 11,000 Km ( 6,214 mi) long Rift Valley – 24 Km (15 mi) wide, 9 Km (6 mi) deep

Divergent boundaries on Continents Crust is to thick to pull apart like in the ocean Two plates still pull apart Faults are created at the edges of these plates Causes lots of earthquakes to occur Middle sinks down Eventually it will sink below sea level and fill with water Red sea

Divergent boundaries on Continents The Great Rift Valley in Africa Thousands of Km long and 1800 m deep Iceland Being split into two islands Process takes millions of years

Tectonic Plates push together at convergent boundaries Crust is either folded or destroyed Subduction When one plate sinks beneath another Major geologic events occur at all convergent boundaries

Continental-Continental Collision When two plates carrying continental crust push together Because both crusts are the same density neither sinks Edges crumple and fold creating mountains Some of the worlds larges mountain chains are formed along these boundaries Alps and Himalayas are examples

Oceanic-Oceanic Subduction This is where one plate with oceanic crust sinks beneath another plate with oceanic crust The older plate sinks It is more dense and colder than the younger plate When the plate reaches the asthenosphere it melts into magma

What main features form at O- O Subduction Deep-Ocean Trenches Like deep canyons that form in the ocean floor as a plate sinks Most are found in the Pacific Ocean The Mariana Trench is where the Pacific Plate is sinking under the Philippine Plate Deepest place in the ocean Nearly 11,000 meters (36,000 ft) down Oldest crust is found at these trenches Earthquakes can occur here

What main features form at O- O Subduction Island Arcs Chain of volcanic islands These are violent volcanoes Examples Philippine Islands Aleutian Islands of Alaska Islands of Japan Earthquakes often happen here

Oceanic-Continental Subduction This is when oceanic crust sinks under continental crust because it is colder and denser Deep-Ocean Trenches also form here These are younger trenches than at O-O subduction Earthquakes also happen here

Oceanic-Continental Subduction Continued Coastal Mountains When the oceanic crust sinks it can cause the continental crust to buckle to form mountains Run parallel to the deep-ocean trench Many of these mountains will also be volcanic Cascade Mountains in Oregon and Washington Mount St. Helens – Active Volcano

Transform Boundaries The only boundary where crust is neither created or destroyed Plates scrape past each other at these boundaries Site of most major earthquakes Most occur on the sea floor but some are on land

Transform Boundaries Continued San Andreas Fault in California Runs from the Gulf of California through San Francisco Pacific Plate and part of the North American Plate are moving in opposite directions If it keeps moving at its current rate Los Angeles will be a suburb of San Francisco in about 10 million years