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RCI Geography A little review… There are three main types of plate boundaries: 1. Divergent boundaries -- where new crust is generated as the plates pull away from each other. 2. Convergent boundaries -- where crust is destroyed as one plate dives under another. 3. Transform boundaries -- where crust is neither produced nor destroyed as the plates slide horizontally past each other. Divergent Plate Boundaries - New crust is created as two or more plates pull away from each other. Oceans are born and grow wider where plates diverge or pull apart. Result: Ridges are created, such as the MidAtlantic ridge and new crust is being created as magma fills this space forming land. • The Mid-Atlantic Ridge, which splits nearly the entire Atlantic Ocean north to south, is probably the best-known and most-studied example of a divergent-plate boundary. • Aerial view of the area around Thingvellir, Iceland, showing a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Right of the fissure, the North American Plate is pulling westward away from the Eurasian Plate (left of the fissure). • East Africa may be the site of the Earth's next major ocean. Plate interactions in the region provide scientists an opportunity to study first hand how the Atlantic may have begun to form about 200 million years ago. Geologists believe that, if spreading continues, the three plates that meet at the edge of the present-day African continent will separate completely, allowing the Indian Ocean to flood the area and making the easternmost corner of Africa (the Horn of Africa) a large island Convergent Plate Boundaries -Occurs when one plate dives under another, creating subduction zones (where you will find mountains or volcanoes) - Crust is destroyed and recycled back into the interior of the Earth We will look at 2 Types of Convergent Boundaries A) Ocean to Continent B) Continent to Continent A) Ocean to Continent - When an oceanic plate pushes into a continental plate, the oceanic plate will slide underneath because it is more dense -The overriding continental plate is lifted up and mountains are created, often in the form of a volcano! Trenches are formed at the point where the oceanic crust dives under (Marianis Trench) Result: Large volcanic chains are created, along with deep-water trenches! • The convergence of the Nazca and South American Plates has deformed and pushed up limestone strata to form towering peaks of the Andes B) Continent to Continent - When two continents meet head-on, neither is subducted because the continental rocks are relatively light - The crust tends to buckle and be pushed upward or sideways Result: Large mountains and mountain chains are created, such as the Himalayas! (Mt. Everest) • The 6,000km-plus journey of the India landmass (Indian Plate) before its collision with Asia (Eurasian Plate) about 40 to 50 million years ago • Sunset view of towering, snow-capped Mt. Everest, from the village of Lobuche (Solu-khumbu), Nepal Who know’s where this is? Transform Boundaries - Transform-Fault Boundaries are where two plates are sliding/grinding horizontally past one another (Like the N.A and Pacific plates) Result: Transform-Fault boundaries are locations of recurring earthquake activity. Most fault boundaries are found in the ocean but the most notable one on land is the San Andreas fault in California (1,300 km long!) • The Blanco, Mendocino, Murray, and Molokai fracture zones are some of the many fracture zones (transform faults) that scar the ocean floor and offset ridges The San Andreas fault zone, which is about 1,300 km long and in places tens of kilometers wide, slices through two thirds of the length of California. Along it, the Pacific Plate has been grinding horizontally past the North American Plate for 10 million years, at an average rate of about 5 cm/yr Hotspots Regions of earthquake and volcanic activity which do not occur along plate boundaries • The vast majority of earthquakes and volcanic eruptions occur near plate boundaries, but there are some exceptions • Map of part of the Pacific basin showing the volcanic trail of the Hawaiian hotspot-- 6,000-km-long Hawaiian RidgeEmperor Seamounts chain What are the consequences of the plates moving? • Formation of new land mid-ocean ridges • Creation of mountains, volcanoes, and trenches from convergent boundaries What are the consequences of the plates moving? • Formation of new land mid-ocean ridges • Creation of mountains, volcanoes, and trenches from convergent boundaries • An area where large numbers of earthquakes and volcanic eruptions occur around the edge of the Pacific Plate • Continuous series of oceanic trenches, volcanic arcs, and volcanic belts. It has 452 volcanoes and is home to over 75% of the world's active and dormant volcanoes, and 90% of the world’s earthquakes