Divergent Plates (Constructive Boundaries) Cause: Plates move in opposite direction due to the convection movement. Effects/Landforms new crust is created (oceanic ridges) Oceans are born and grow wider When 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. Earthquakes Volcanoes
Oceanic-Oceanic The 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.
Formation of Oceanic Ridge (answer) As the N. American and Eurasian plates move apart (divergent movement) in a constructive boundary due to convection currents Tensional stresses cause fractures in the lithosphere to occur The 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 formed The mountains closest to the spreading zone are the youngest The rows of mountains rise from 2,000 to 4,000m from the ocean floor – these are the mid-oceanic ridges Eg: Mid-Atlantic Ridge
Continental-Continental As the Nubian and Somalian plates move apart, They are stretched and fractures are created The land in between sinks, creating a linear depression, known as a rift valley As a result, earthquakes are experienced in the region Magma may also rise to the surface creating volcanoes Eg: the East African Rift Valley
Oceanic-Oceanic The Japanese Islands are examples of volcanic island arcs formed by the convergence of two oceanic plates.
Cause: 2 oceanic plates collide One plate sinks beneath the other Subduction zone Effects/Landforms: Trench Volcanoes Earthquake
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 plate The oceanic plate descends beneath the continental This descent is called subduction The old oceanic lithosphere is destroyed and as it dives to the mantle, it contributes to the formation of more magma A long narrow and deep oceanic trench is formed where the plate dips into the mantle Eg: Peru-Chile Trench, Java Trench Name of plates
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 magma Being less dense than the mantle, the magma moves up any break or fractures When it escapes through vents to the land surface, it forms subduction volcanoes Eg: Mt. St. Helens, Mt Pinatubo
Oceanic-Continental Cause: Oceanic plate collides with thinner & lighter continental plate Subduction occurs Effects/Landforms Descending plate is destroyed Trenches are formed Volcanoes Earthquakes
Formation of Fold Mountains (answer) When two continental masses collide, one is pushed under the other for a short distance When a thinner and denser oceanic plate converges with a thicker and lighter continental plate The oceanic plate descends beneath the continental This descent is called subduction The old oceanic lithosphere is destroyed and as it dives to the mantle, it contributes to the formation of more magma The edges of these plates are also contorted and buckled up, creating a great uplift, forming fold mountains Since 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
Continental-Continental Cause: 2 continental plates collide No subduction Effects/Landforms Great uplift Rocks are contorted Earthquakes Earthquakes are shown as yellow squares.
Formation of Fold Mountains (answer) When two continental masses collide, the Indian plate is pushed under the Eurasian plate for a short distance However, there is NO subduction Because both are light and buoyant This process produces a great uplift as the rocks at the edges of these two plates are contorted and buckled up Due to the absence of magma supply, there are no volcanoes in this area Eg: the Himalayan Mountains
Transform Boundaries occur 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 transform boundaries occur in short segments along mid-oceanic ridges
https://www.youtube.com/watch?v =0mWQs1_L3fA Sit back and relax… well… can’t be too relaxed… Here’s a summary… don’t fall asleep
References Chong, Marianne (2001) Aspects of Physical Geography Waugh, David (2009) Geography: An Integrated approach