There are four types of plate boundaries: There are four types of plate boundaries:

1. Divergent boundaries -- where new crust is generated as 1. Divergent boundaries -- where new crust is generated as the plates pull away from each other. the plates pull away from each other.

2. Convergent boundaries -- where crust is destroyed as one 2. Convergent boundaries -- where crust is destroyed as one plate dives under plate dives under another. another. 3. Transform boundaries -- where crust is neither produced 3. Transform boundaries -- where crust is neither produced

nor destroyed as the plates slide horizontally past each othernor destroyed as the plates slide horizontally past each other.

4. Plate boundary zones -- broad belts in which boundaries 4. Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are are not well defined and the effects of plate interaction are unclearunclear

Divergent Plate Divergent Plate BoundariesBoundaries

• The Mid-Atlantic The Mid-Atlantic Ridge, which Ridge, which splits nearly the splits nearly the entire Atlantic entire Atlantic Ocean north to Ocean north to south, is probably south, is probably the best-known the best-known and most-studied and most-studied example of a example of a divergent-plate divergent-plate boundary.boundary.

• Aerial view of the Aerial view of the area around area around Thingvellir, Thingvellir, Iceland, showing a Iceland, showing a fissure zone (in fissure zone (in shadow) that is the shadow) that is the on-land exposure of on-land exposure of the Mid-Atlantic the Mid-Atlantic Ridge. Right of the Ridge. Right of the fissure, the North fissure, the North American Plate is American Plate is pulling westward pulling westward away from the away from the Eurasian Plate (left Eurasian Plate (left of the fissure).of the fissure).

• East Africa may be the site of the Earth's East Africa may be the site of the Earth's next major ocean. Plate interactions in the next major ocean. Plate interactions in the region provide scientists an opportunity to region provide scientists an opportunity to study first hand how the Atlantic may have study first hand how the Atlantic may have begun to form about 200 million years ago. begun to form about 200 million years ago. Geologists believe that, if spreading Geologists believe that, if spreading continues, the three plates that meet at the continues, the three plates that meet at the edge of the present-day African continent will edge of the present-day African continent will separate completely, allowing the Indian separate completely, allowing the Indian Ocean to flood the area and making the Ocean to flood the area and making the easternmost corner of Africa (the Horn of easternmost corner of Africa (the Horn of Africa) a large islandAfrica) a large island

Convergent Plate Convergent Plate BoundariesBoundaries

3 Types of Convergent Boundaries3 Types of Convergent Boundaries

Ocean to ContinentOcean to Continent

Ocean to OceanOcean to Ocean

Continent to ContinentContinent to Continent

• The The convergence convergence of the Nazca of the Nazca and South and South American American Plates has Plates has deformed deformed and pushed and pushed up limestone up limestone strata to strata to form form towering towering peaks of the peaks of the AndesAndes

• The 6,000-The 6,000-km-plus km-plus journey of journey of the India the India landmass landmass (Indian (Indian Plate) Plate) before its before its collision collision with Asia with Asia (Eurasian (Eurasian Plate) Plate) about 40 to about 40 to 50 million 50 million years agoyears ago

• Sunset view of towering, snow-capped Mt. Everest, Sunset view of towering, snow-capped Mt. Everest, from the village of Lobuche (Solu-khumbu), Nepalfrom the village of Lobuche (Solu-khumbu), Nepal

Transform BoundariesTransform Boundaries

• The Blanco, The Blanco, Mendocino, Mendocino, Murray, and Murray, and Molokai Molokai fracture fracture zones are zones are some of the some of the many many fracture fracture zones zones (transform (transform faults) that faults) that scar the scar the ocean floor ocean floor and offset and offset ridgesridges

• The San Andreas fault The San Andreas fault zone, which is about zone, which is about 1,300 km long and in 1,300 km long and in places tens of places tens of kilometers wide, slices kilometers wide, slices through two thirds of through two thirds of the length of the length of California. Along it, California. Along it, the Pacific Plate has the Pacific Plate has been grinding been grinding horizontally past the horizontally past the North American Plate North American Plate for 10 million years, at for 10 million years, at an average rate of an average rate of about 5 cm/yrabout 5 cm/yr

HotspotsHotspots

Regions of earthquake and volcanic Regions of earthquake and volcanic activity which do not occur along activity which do not occur along

plate boundariesplate boundaries

• The vast majority of earthquakes and volcanic eruptions The vast majority of earthquakes and volcanic eruptions occur near plate boundaries, but there are some occur near plate boundaries, but there are some exceptionsexceptions

• Map of part of the Pacific basin showing the volcanic trail Map of part of the Pacific basin showing the volcanic trail of the Hawaiian hotspot-- 6,000-km-long Hawaiian Ridge-of the Hawaiian hotspot-- 6,000-km-long Hawaiian Ridge-Emperor Seamounts chainEmperor Seamounts chain