TECTONIC LANDSCAPES

Memory challenge 1

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A- How to describe distributions of earthquakes and volcanoes1- recognise the overall distribution2- describe the distribution in more detail. Use oceans/continents in your description.3- is there any exception to the distribution described at 1 and 2?

Volcanoes and earthquakes occur in narrow belts (overall distribution). The largest belt runs around the

Pacific Ocean, along the edge of continents.

Example 1: Map without plate boundaries

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Other bands are found in the middle of oceans such as the belt that extends down the entire

length of the mid-Atlantic Ocean.

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Another major belt travels through the continents of Europe and Asia and Eastern

Africa.

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Map of the distribution of volcanoes with plate boundaries

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1- Volcanoes occur in narrow belts along plate boundaries.

2-The largest belt runs around the Pacific Ocean, near convergent boundaries.

3-Many volcanoes are found either along the edge of the North American and South American continents or form volcanic islands in the Pacific Ocean.

4-There are some volcanoes along the northern part of the Mid-Atlantic Ridge.

5-Some volcanoes are located far from plate boundaries such as the Hawaiian hotspot in the Pacific Ocean.

Be able to name the features produced at each type of boundary and to explain how they are

formed.

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Depending on the direction of the convection currents in the mantle, the plates can move•Towards each other (convergent)•Away from each other (divergent)•Slide past each other (transform)

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Oceanic crust

1-Convection currents pull plates apart. 3-As the plates move apart,

magma from the mantle rises to fill the gap and forms new oceanic crust.

4-A mid-ocean ridge is formed by the new crust. 5-Submarine

volcanoes appear along the ridge. Some may grow to form volcanic islands, e.g. Iceland.

6- Earthquakes are caused by volcanic eruptions or by plates moving apart.

Oceanic crust

2-This leads to a gap being formed in the crust.

Divergent or constructive boundariesDivergent or constructive boundaries

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Describe and explain the characteristic features of a constructive boundary. (4)

What are the features? Mid-ocean ridges, volcanic islands and earthquakes 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.

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Destructive/Convergent boundaries

A- Oceanic-continental boundariesB- Continental-continental boundaries

C- Oceanic-oceanic boundaries

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Ocean-to-continent boundary

Nazca Plate(Oceanic)

South AmericanPlate (Continental)

Mantle

PacificOcean VolcanoTrench

Andes fold mountains

Subductionzone

2-The Nazca Plate (oceanic) is being subducted below the South American Plate (continental).

3-Friction and pressure cause earthquakes to occur along the subduction zone

4-The heat fromthe mantle causes the oceanic plate to be destroyed.

5-The melting platecreates lighter magma that risestowards the surfaceto form volcanoes.

6-The Peru-Chile trenchforms where the oceanic plate is beingsubducted.

7-The collision causesfolding and uplift ofrocks which form foldmountains.

Earthquakes

1-The Nazca Plate and the South American Plate move towards each other due to convection currents.

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b- Continental-to-continental boundary

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1- When two continental plates meet at a destructive boundary, a slow collision takes place as both plates have a low density.

2- This results in intense folding and uplift and leads to the formation of fold mountains.

3- There is no subduction. Therefore, there are no volcanoes.

4- However, earthquakes occur due to the collision of the plates.

Ocean-to-ocean boundaries

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Philippine PlatePhilippine PlateEurasianPlateEurasianPlate

Ryuku Islands (Japan)Ryuku Islands (Japan)

2-The Philippine Plate is subducted beneath the Eurasian Plate.

2-The Philippine Plate is subducted beneath the Eurasian Plate.1- Due to convection

currents in the mantle, the two oceanic plates collide.

1- Due to convection currents in the mantle, the two oceanic plates collide.

3- As it is subducted, friction and pressure cause earthquakes along the subduction zone.

3- As it is subducted, friction and pressure cause earthquakes along the subduction zone.

Subduction zoneSubduction zone

4- As the Philippine plate begins to melt, magma escapes to the surface to form volcanoes, a few kilometres from the trench.

4- As the Philippine plate begins to melt, magma escapes to the surface to form volcanoes, a few kilometres from the trench.

5- After several eruptions, these volcanoes break the ocean surface to form islands

5- After several eruptions, these volcanoes break the ocean surface to form islands

6- When several volcanic islands form together they are called an island arc.

6- When several volcanic islands form together they are called an island arc.

Conservative [transform] boundaries

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The San Andreas Fault in California marks the junction of the North American and Pacific plates. Both plates are moving north-west but at different speeds. Instead of slipping smoothly past each other, they tend to ‘stick’. The pressure builds up until suddenly the plates move forward and an earthquake occurs. There is no volcanic action because the crust is not being destroyed.

Plates just slide past each other with crust neither created nor destroyed. Friction builds up and energy is released when the plates move forward, causing earthquakes.