PLATE BOUNDARIES

• Divergent boundaries - plates that separate and move apart in opposite direction
• Divergent boundary is also known as constructive boundary
• Convergent boundaries - when two plates move towards each other.
• Convergent boundary is also known as destructive boundary
• Transform-fault boundary - two plates are sliding past each other.
• Rocks that line the boundary split into pieces as the plates split at each other, forming a crack that creates an undersea canyon.
• 3 types of convergence: continental-continental, continental-oceanic, oceanic-oceanic
• In continental-oceanic convergence, it involves the convergence of a land plate and ocean plate, then the denser oceanic crust undergoes subduction process.
• Subduction - bending of the crust towards the mantle.
• Since the mantle is hotter, the subducted crust melts, forming magma.
• Geological features forming in continental-oceanic convergence are earthquake, trench, tsunami, formation of volcanic arc.
• One important geologic feature formed for the oceanic crust is the trench.
• Ocean trenches - deepest part of the ocean.
• In oceanic-oceanic convergence, two ocean plates converge forming trenches.
• Trenches will be the source of earthquake
• Underwater earthquakes can generate tsunamis. The Japanese term for harbor wave is tsunami.
• Tsunami - series of ocean waves with very long wavelengths caused by large-scale disturbance of the ocean.
• Volcanic island arc is always parallel to the trench
• In oceanic-oceanic convergence, the leading edge of subducted plate will eventually reach the mantle causing it to melt and turn to magma, then the molten material will rise to the surface creating volcanic island arc.
• Geological features formed in oceanic-oceanic convergence are volcanic island arc, trenches, tsunami.
• In continental-continental convergence, two land plates collide which forms mountain.
• The only noticeable geologic feature in continental-continental convergence is the formation of mountain ranges.
• In continental-continental convergence, there is no earthquake
• The movement of plates per year in continental-continental convergence is 2-20km
• When an oceanic plate converges into a continental plate, the denser oceanic plate gets pushed down beneath the less dense continental plate forming a deep trench.
• Continental-continental convergence is also known as collision boundary or conservative boundary.
• The Philippine archipelago is formed with an oceanic-oceanic convergence.
• In Divergence of plates, Rift valleys and Oceanic ridges are the indications that the crust are splitting apart.
• Most divergent boundaries are situated along the underwater mountain ridges called oceanic ridges.
• Mid-Atlantic Ocean Ridge is an example of spreading center which causes the divergence of the South American Plate and African plate.
• Rift Valleys are formed from the divergence of two continental plates
• Oceanic ridge is formed by the divergence of two oceanic plates
• Transform Fault occurs within the boundaries of plates. It occurs in continental-continental and oceanic-oceanic
• Divergent of crust must happen first before we can observe transorm fault.
• An example of transform fault is the San Andreas fault.
• The only geological feature observed in transform fault is earthquake.
• Mantle Plume - where magma goes out or exits
• The volcano nearest from the mantle plume is identified to be he youngest.
• The volcano farthest from the mantle plume is identified to be the oldest.
• Trench - a depression in the seafloor produced by the subduction process.