The main physical features of the Earth. 1 Atlantic Ocean Indian Ocean Pacific Ocean Southern Ocean North America South America Africa Europe Asia Oceania Antarctica Rocky Mountains Andes Alps Himalayas

Definition of ‘Plate tectonics’ A plate is a large, rigid slab of solid rock. The word tectonics comes from the Greek root "to build." Putting these two words together, we get the term plate tectonics, which refers to how the Earth's surface is built of plates. The theory of plate tectonics states that the Earth's crust is broken into a number of large and small slabs of rock called plates. The formation of mountains and volcanoes, and the occurrence of earthquakes have been explained using this theory. 2

CROSS-SECTION OF THE EARTH 3 CRUST: SOLID THIN LAYER. MADE OF TWO MAIN TYPES: -CONTINENTAL (60 KM THICK) -OCEANIC (8 TO 10 KM THICK) (MUCH HEAVIER THAN CONTINENTAL) DIVIDED INTO PLATES WHICH FLOAT ON THE MANTLE MANTLE: MOLTEN ROCK WHICH MOVES IN CIRCLES DUE TO CONVECTION CURRENTS THE CORE GIVES OFF INCREDIBLE HEAT WHICH CAUSES THE MANTLE TO FLOW.

How plates move 4 Huge convection currents occur in the mantle. The cause of these currents is radioactive decay in the core. Motion is driven by friction between the solid top layer of the earth [crust] and the semi-liquid layer below [mantle].

The importance of crust 5 There are two types of crust which have different characteristics. Older, lighter, cannot sink and is permanent. Younger, heavier, can sink and is constantly being destroyed and replaced.

World map of plate boundaries 6

Label the map with the name of the plates in Figure 4 7

Plate boundaries The boundaries between plates can be classified into three main types according to the direction of movement of the plates on either side of the boundary. Plates may either move away from each other (divergence), towards each other (convergence), or past each other. 8

9 MANTLE

Destructive/convergent boundaries Plates collide. The oceanic crust which is denser is forced beneath the lighter continental crust. This process is called subduction. The descending plate creates friction and a build-up of pressure which causes partial melting of the crust and earthquakes. Magma from below the crust can rise to form volcanoes. 10

B- Ocean-to-continent boundary 11 Nazca Plate (Oceanic) South American Plate (Continental) Mantle Pacific Ocean Volcano Trench Andes fold mountains Subduction zone 1-The Nazca Plate is being subducted below the South American Plate. 2-Friction and pressure cause earthquakes to occur along the subduction zone 3-The heat from the mantle causes the oceanic plate to be destroyed. 4-The melting plate creates lighter magma that rises towards the surface to form volcanoes. 5-The Peru-Chile trench forms where the oceanic plate is being subducted. 6-The collision causes folding and uplift of rocks which form fold mountains. Earthquakes

Draw, label and annotate 12

Fold Mountains along destructive margins: The Andes 13 The Andes are located where the Nazca Plate, made of dense oceanic crust, is subducted beneath the South American Plate, made of lighter continental crust. More than 100 million years ago, the Andes began to form by the uplifting and folding of sedimentary rocks accumulated along the edge of the continental plate. Massive layers of rock got folded by compressional forces as a result and formed a narrow belt along the western edge of the continent. During the last 20 million years, parts of the Andes have been lifted over 1500 m. Massive layers of rock got folded by compressional forces

2- Constructive/divergent boundary As plates move apart, magma comes to the surface, forming new crust on the ocean floor at the mid-ocean ridges and forcing plates apart. When the magma builds up above the surface of the ocean, volcanic islands form, e.g. Iceland Next slide shows the mid-Atlantic Ridge which marks the divergent boundary in the Atlantic Ocean. 14

15 Oceanic crust 1-Convection currents pull plates apart. 2-As the plates move apart, magma from the mantle rises to fill the gaps and forms new oceanic crust. 3-A mid-ocean ridge is formed by the new crust. 4-Submarine volcanoes appear along the ridge. Some may grow to form islands, e.g. Iceland. Oceanic crust

Draw, label and annotate 16

17 Mid-Atlantic ridge

Surtsey [volcanic island near Iceland]

Describe and explain the characteristic features of a constructive boundary. (4) What are features? Mid-ocean ridges and volcanic islands are the features of a constructive boundary. The question asks for an explanation, i.e. the reasons for these features. You may answer this question using the ‘case study’, i.e. located example, of the Mid-Atlantic constructive boundary. 19

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Why do some volcanoes not occur on plate boundaries?... Hot spots 21

Understanding hotspots Some volcanoes do not occur on plate boundaries. These volcanoes are formed over hotspots. These are fixed points in the mantle that generate intense heat. Small, long lasting, exceptionally hot areas of magma exist under the Earth's surface which in turn sustains long- lasting volcanic activity. 22

At areas where the pressure is greater in the mantle, magma erupts through the crust as when the plume reaches the crust it causes the crust to dome (and crack). Volcanoes are created if the magma rises above the ocean surface. As the crustal plate moves over the stationary hotspot, new volcanoes are formed. Hotspots are associated with chains of islands such as Hawaii. 23

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As the plate moves over the stationary hotspot, new volcanoes are formed. 25

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Case study: The Hawaiian Islands, which are entirely of volcanic origin, have formed in the middle of the Pacific Ocean more than 3,200 km from the nearest plate boundary. The Hawaiian Islands are located over a hotspot. The magma rises through the Pacific Plate to supply the active volcanoes. 27