Constructive Margin: Oceanic§ Oceanic Constructive Margins are found when two tectonics plates move away from each other in the ocean. Magma then rises to fill the gap created, forming new ocean floor.§ An example of this is the Mid-Atlantic Ridge, which is caused by the North Atlantic and the Eurasian Plate moving away from each other, causing new ocean floor to be formed along the ridge. This means that North America and Europe are moving further away from each other TM,1
Constructive Margins: Continental E.G. Eurasian, North American tectonics plate 1. This type of margin is developed where rising mantle convection currents occur below a continental plate. 2. The rising hot mantle material causes the overlying continental plate to dome up and stretch. 3. Stretching of the relatively rigid plate causes brittle fractures to develop, and the plate eventually cracks. 4. As the mantle convection currents diverge, the plate is gradually pulled apart and the central blocks between the faults sink downwards, forming a rift valley. 5. Movement between the different fragments of crust in the rift valley causes frequent shallow focus earthquakes. RA, 2
§ AW - Destructive Margin – Oceanic-Continental§§ §§ Where the two meet the oceanic crust is more dense than the continental, as such it is subducted.§ § Example – Nazca plate is being subducted under the South American plate forming the Andes mountain range.§ § Location of many shallow to deep focus quakes as the oceanic plate sticks and slips underneath the continental plate.§ Volcanic arc chains on-shore§ Aw, 3
Oceanic – Oceanic Destructive Plate Boundaries When a convergent boundary occurs between two oceanic plates one of those plates will subduct beneath the other. Normally the older plate will subduct because of its higher density. The subducting plate is heated as it is forced deeper into the mantle and begins to melt. Magma chambers are produced as a result of this melting and the magma is lower in density than the surrounding rock material. Magma chambers that reach the surface break through to form a volcanic eruption cone. Eventually the cones will grow to be higher than sea level. This produces an island chain. With continued development the islands grow larger, merge and an elongate landmass is created.The Mariana Trench is an example of a SPM, 4 oceanic- oceanic plate boundary
COLLISIONMARGINS• When two continental crusts collide, neither of them can sink.• This means the force of them pushing into each other all goes upwards. This forms mountain ranges.• This pressure and movement can cause an earthquake, but will not form a volcano.• An example of a major collision is when the Eurasian and Indian Plates collided, forming the Himalayas.• Landmass can also be pushed aside by this. East Asia is still moving away from the ‘collision zone’, forced away by the pressure. CW,5
Conservative plate boundaries - San Andreas FaultThe main effects of a conservative plate boundary are earthquakes, which can be fairly violent and frequent.Two plates slide past each other, without creating or destroying any land.As they move past each other they often get stuck, building up great pressure until finally they jolt past each other. This sudden movement is what causes earthquakes. • The San Andreas fault is a conservative plate boundary between the Pacific and North American plates which runs 1200 km across California, in the west of the US. • There have been two large earthquakes caused by the fault: in 1857 and 1906. In the latter 3000 people died. AH, 6
Hot Spots Hot spots are areas on the Earth’s crust above anomalously hot areas of magma. Volcanic activity occurs when the magma rises to the surface and erupts as lava. Sometimes, instead of creating a volcano, the magma will heat groundwater under the Earth’s surface, which causes water and steam to erupt as geysers. There are around 40-50 hotspots in the world. Hotspots produce Iceland’s hot springs and are the source of most geothermal energy. The island chain of Hawaii was created by a hotspot continuously spewing lava as the pacific plate it was located on shifted. Scientists can use hotspots to track the movement of tectonic plates. Nobody is entirely clear what causes hotspots. CT, 7
Fold Mountains • Fold mountains occur near convergent or compressional plate boundaries. • Examples of fold mountains include the Alps, Rockies, Andes and Himalayas Example : Matterhorn, Zermatt, Switzerlandq High mountain ranges, e.g. 1. Where an area of sea separates Mont Blanc, which is 4,810 two plates, sediments settle m above sea level. on the sea floor in depressionsq Glaciated valleys, e.g. the called geosynclines. Rhone Valley. 2. These sediments graduallyq Pyramidal peaks, e.g. the become compressed into Matterhorn. sedimentary rock.q Ribbon lakes, e.g. Lake Como. v When the two plates move towards each other again, theq Fast-flowing rivers. layers of sedimentary rock on the sea floor becomeq Contrasting microclimates on crumpled and folded. north facing and south v Eventually the sedimentary rock appears above sea level as facing slopes. a range of fold mountains. SH,8
Ocean Trenches§ Narrow, elongated, V-shaped depression in the ocean floor§ Formed when oceanic plate dives below overriding plate§ Associated with island arcs and high earthquake activity§ Examples are the Aleutian islands and the Mariana trench, the deepest in the world GL, 9
Island ArcsIsland arcs are archipelagos of islands thatrun along a plate boundary, and areformed when an oceanic plate subductsanother oceanic plate, which normallycauses magma to rise up and formvolcanoes – there are examples all over theworld, including the South AegeanVolcanic Arc in Greece, and thePhilippines. There are also non-volcanicisland arcs, such as the Hellenic Arc whichis parallel to the South Aegean Arc. AO, 10
OceanRidges A mid ocean ridge is the general term for an underwater mountain system. It is formed when two oceanic plates move away from each other and lava rises. This cools at the surface to form an ‘underwater mountain range’. Example: MID ATLANTIC RIDGE Divergent plate boundary. Split between the North and South of the Atlantic. Around 2.5cm per year (splitting distance) ST,OK 11
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