Plate tectonics Volcano

1 plate tectonics

1.1 divergent plate boundaries
1.2 convergent plate boundaries
1.3 hotspots

plate tectonics

map showing divergent plate boundaries (oceanic spreading ridges) , recent sub-aerial volcanoes



divergent plate boundaries

at mid-oceanic ridges, 2 tectonic plates diverge 1 new oceanic crust formed cooling , solidifying of hot molten rock. because crust thin @ these ridges due pull of tectonic plates, release of pressure leads adiabatic expansion (without transfer of heat or matter) , partial melting of mantle, causing volcanism , creating new oceanic crust. divergent plate boundaries @ bottom of oceans; therefore, volcanic activity on earth submarine, forming new seafloor. black smokers (also known deep sea vents) evidence of kind of volcanic activity. mid-oceanic ridge above sea-level, volcanic islands formed; example, iceland.

convergent plate boundaries

subduction zones places 2 plates, oceanic plate , continental plate, collide. in case, oceanic plate subducts, or submerges, under continental plate, forming deep ocean trench offshore. in process called flux melting, water released subducting plate lowers melting temperature of overlying mantle wedge, creating magma. magma tends extremely viscous because of high silica content, not attain surface cools , solidifies @ depth. when reach surface, however, volcano formed. typical examples mount etna , volcanoes in pacific ring of fire.

hotspots

hotspots volcanic areas believed formed mantle plumes, hypothesized columns of hot material rising core-mantle boundary in fixed space causes large-volume melting. because tectonic plates move across them, each volcano becomes dormant , re-formed plate advances on postulated plume. hawaiian islands said have been formed in such manner; has snake river plain, yellowstone caldera being part of north american plate above hot spot. theory, however, has been doubted.