3 Divergent Plates (Constructive Boundaries) Cause:Plates move in opposite direction due to the convection movement.Effects/Landformsnew crust is created (oceanic ridges)Oceans are born and grow widerWhen a diverging boundary occurs on land a 'rift', or separation will arise and over time that mass of land will break apart into distinct land masses and the surrounding water will fill the space between them.EarthquakesVolcanoes
4 Oceanic-OceanicThe divergent Mid-Atlantic Ridge rises above sea level at Thingvellir, with the North American plate to the west and the Eurasian plate to the east.
5 Formation of Oceanic Ridge (answer) As the N. American and Eurasian plates move apart (divergent movement) in a constructive boundary due to convection currentsTensional stresses cause fractures in the lithosphere to occurThe zone where the plates separate is the spreading centre,Allowing basaltic magma to well up, cool and solidify; thus becoming / forming new sea floor (this process is called sea floor spreading)As the plates continue to move apart, more basaltic magma piles up, cool and solidify; and new mountains are formedThe mountains closest to the spreading zone are the youngestThe rows of mountains rise from 2,000 to 4,000m from the ocean floor – these are the mid-oceanic ridgesEg: Mid-Atlantic Ridge
6 Continental-Continental As the Nubian and Somalian plates move apart,They are stretched and fractures are createdThe land in between sinks, creating a linear depression, known as a rift valleyAs a result, earthquakes are experienced in the regionMagma may also rise to the surface creating volcanoesEg: the East African Rift Valley
10 Formation of Trench and volcanoes (answer) Trench in a convergence between Oceanic and Continental Plate (destructive boundary)When a thinner and denser oceanic plate converges with a thicker and lighter continental plateThe oceanic plate descends beneath the continentalThis descent is called subductionThe old oceanic lithosphere is destroyed and as it dives to the mantle, it contributes to the formation of more magmaA long narrow and deep oceanic trench is formed where the plate dips into the mantleEg: Peru-Chile Trench, Java TrenchName of plates
11 The movement of the plates cause faults to occur Rocks break and are displaced relative to each other,the melting of the subducting oceanic plate produces silica-rich magmaBeing less dense than the mantle, the magma moves up any break or fracturesWhen it escapes through vents to the land surface, it forms subduction volcanoesEg: Mt. St. Helens, Mt Pinatubo
12 Oceanic-Continental Cause: Oceanic plate collides with thinner & lighter continental plateSubduction occursEffects/LandformsDescending plate is destroyedTrenches are formedVolcanoesEarthquakes
13 Formation of Fold Mountains (answer) When two continental masses collide, one is pushed under the other for a short distanceWhen a thinner and denser oceanic plate converges with a thicker and lighter continental plateThe oceanic plate descends beneath the continentalThis descent is called subductionThe old oceanic lithosphere is destroyed and as it dives to the mantle, it contributes to the formation of more magmaThe edges of these plates are also contorted and buckled up, creating a great uplift, forming fold mountainsSince sediments from the ocean floor are contorted and uplifted, marine fossils were found at the summit of fold mountains!!!Eg: Rocky Mountains (N. America), Andes Mountains (South America)Name of plates
14 Continental-Continental Cause:2 continental plates collideNo subductionEffects/LandformsGreat upliftRocks are contortedEarthquakes Earthquakes are shown as yellow squares.
15 Formation of Fold Mountains (answer) When two continental masses collide, the Indian plate is pushed under the Eurasian plate for a short distanceHowever, there is NO subductionBecause both are light and buoyantThis process produces a great uplift as the rocks at the edges of these two plates are contorted and buckled upDue to the absence of magma supply, there are no volcanoes in this areaEg: the Himalayan Mountains
16 Transform Boundariesoccur in a few places to accommodate lateral motion, in which plates slide past one another.very rare on continents, but they are dramatic where they do occur. Example: the San Andreas Fault (USA) and The Alpine Fault (New Zealand).Most transformboundaries occur in shortsegments alongmid-oceanic ridges
17 Sit back and relax… well… can’t be too relaxed… Here’s a summary… don’t fall asleephttps://www.youtube.com/watch?v=0mWQs1_L3fA
18 References Chong, Marianne (2001) Aspects of Physical Geography Waugh, David (2009) Geography: An Integrated approach