Geography NotesChapter 1 : Plate TectonicsCauses of Pate MovementCrustal plates resting on mantle are constantly inmotion due to movement of magma . Heated Magmaexpands and pushes plates away from eachother .(Plate divergence) Cooled magma contracts and sinks pulling plates together .Oceanic-Oceanic plate divergenceExplanation:1. When Rising Convection currents push two plates away from each other .2. Fractures and cracks develop at plate boundaries3. Constant flow of lava( formerly magma) causes formation of new crusts while pushing old crusts further apart. SEAFLOOR SPREADING and is considered constructive as new crusts are made4. Oceanic Ridges are formed. Examples of oceanic ridges Mid Atlantic Ridge Formed by Eurasian plate and north American plate Formed ICELAND ( volcanic Island) Continental-continental plate divergence Examples African plate & Eurasian plate When two continental crusts diverge, forming a depression of a rift valley . Ex. East African Rift Valley
Convergent Plate MovementWhen forces of compression move plates towards each otherDenser Plate subducts less denser plate is pushed upType 1. Oceanic – Continental Convergence 1. The less denser plate is pushed up while the Denser plate subducts into the molten mantle And is destroyed. 2. Development of long narrow and deep oceanic trench 3. Less dense plate rises and fold to form fold mountains . Example Oceanic Nazca Plate & continental South American Plate ( Diagram Above) 1. Nazca Plate pushed against the South American Plate. 2. Denser American Plate is subducted beneath the less dense south American Plate 3. Subducted Nazca Plate melts and forms Magma . 4. Magma from mantle escapes through vents and erupts 5. Erupted Materials such as lava and pyroclastics bulid up over time and form volcanoes 6. Overlying continental South American Plate is pushed up to form mountains called the ANDES MOUNTAINs 7. Active volcanoes are present at convergent plate boundaries.Type 2.Oceanic –Oceanic Plate ConvergencePacific plate & Philippines plate 1. Oceanic trenches are developed 2. Chain of subduction volcanoes called The MARIANAS ISLANDS Type3. Continental – Continental Plate convergence Both crusts have equal density thus no subduction happening So area between crust is highly contorted and warped Examples, Eurasian & Indian Plate Fold mountains formed : THE HIMALAYAS
Explanation of Divergent Plate Movement being CONSTRUCTIVEDevelopment of liner features along the plate boundary . Due to the eruption of lava when theplates diverge, new crust is formed and the old crust are pushed away , further from each other thusas new crusts are formed , divergent plate movement Is considered as constructive.Explanation of Convergent plate movement being DESTRUCTIVEWhen two plates move towards each other , either subduction or plate collision happens . Forsubduction, the denser plate is destroyed in the mantle . For plate collision , due to the intensepressure from the plates puhing against each other EARTHQUAKES , EXPLOSIVE VOLCANOES arecommon at plate boundaries , thus the plates are deformed and destroyed at convergent plateboundaries thus it is considered as DESTRUCTIVETransform Plate BoundryExplanation: lateral movement of plates as they slide pass each other .Examples: San Andreas Fault .North American Plate Pushing South Eastwards & Pacific Plate pushing North Westwards.Effects : 1. Tremendous stress build up at one of contact 2. Fracture Zones 3. Distorted Alignment of land and infranstructure 4. Devasating Earthquakes 5. Collaspse & buring of properties and lives 6. 1906 San Francisco Earthquake took >3000 lives and caused widespread damage.