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Why do the plates move? Crust Convention Currents Mantle 1 of 26 © Boardworks Ltd 2003 Eurasian North American Pacific African Plate Nazca South American Indo Australian Plate Antarctic Plate Names 2 of 26 © Boardworks Ltd 2003 Mid-Atlantic ridge Sea Floor Spreading! Did you know that the ocean floor in the Atlantic is growing by 3cm per year? Which of the following pairs of continents are moving further away from each other? 1) Europe and Africa 2) Europe and North America 3) South America and North America 3 of 26 © Boardworks Ltd 2003 Constructive Plate Boundary At a constructive plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill the gap. This causes volcanoes at this type of boundary. However, since the magma can escape easily at the surface the volcano does not erupt with much force. Earthquakes are also found at constructive boundaries. An example of a constructive boundary is the Mid-Atlantic Ridge. 4 of 26 © Boardworks Ltd 2003 A destructive plate boundary is found where a continental plate meets an oceanic plate. Destructive Plate Boundary 5 of 26 The oceanic plate descends under the continental plate because it is denser. As the plate descends it starts to melt due to the friction caused by the movement between the plates. This melted plate is now hot, liquid rock (magma). The magma rises through the gaps in the continental plate. If it reaches the surface, the liquid rock forms a volcano. © Boardworks Ltd 2003 Conservative plate boundaries exist where two plates do not directly collide but slide past each other along a fault (weakness). Conservative Boundary No volcanoes are found along these plate boundaries, but earthquakes do occur. An example of such a boundary is the San Andreas Fault in California. 6 of 26 © Boardworks Ltd 2003 Name this plate boundary A G B E C F D Match the labels to the letters Earthquakes occur due to friction The oceanic crust sinks under the less dense continental crust Oceanic plate Continental crust 7 of 26 Explosive volcanoes The oceanic crust melts and rises Mantle © Boardworks Ltd 2003 Constructive plate boundaries MID OCEAN RIDGE B A Ocean Mantle Where would you find older rocks – at A or at B? 8 of 26 © Boardworks Ltd 2003
