1. What are tectonic hazards and what causes them?

2. Objectives
To think about what we already know on the topic of tectonics.
Understand the structure of the Earth and how it is divided into plates.
Investigate the evidence for continental drift.

3. Introduction
The earths surface is constantly changing, sometimes this is slowly and at other times it is very quickly. Some of the changes occur at the earths surface, but there are other changes taking place deep inside the earth.

4. The structure of the Earth
The Earth is divided into three main layers.
The Crust
The Mantle
The Core
Use the diagram above to label the main layers of the earth.

5. Plate Tectonics
The Earth is divided into a series of plates. It is the study of these plates and their movements that is known as plate tectonics.

6. Evidence for Continental Drift
The plates that make up the earths surface are slowly moving over time. This movement is known as continental drift.
In 1912 a scientist called Alfred Wegner claimed that the Earth was once comprised of a huge supercontinent called Pangaea which over time has broken up and drifted into its current position.
Wegner’s evidence for this was drawn from several sources, covering geology, biology, palaeontology and geography.

7. Movement

8. Solving the mystery
You will investigate some of the different pieces of evidence for continental drift.
Using the sources provided produce a brief report showing the evidence for continental drift.
Use the following headings to show the evidence.
Jigsaw fit, Paleomagnetism, Geology, Fossils, Climatic.

9. Fossil evidence
Lystrosaurus a large mammal like dinosaur.Fossils have been found in Africa, India and Antarctica. This dinosaur can not swim or fly.
Fossils of the fern Glossopteris have been found in all southern continents.

10. Paleomagnetism
Ships have been used to map the magnetic orientation of the rocks.
As new rock has been created in the centre of the ocean older rocks are pushed to the edges.
Every time new rock has been created it has the magnetic orientation of the time imprinted in it.

11. This shows the magnetic orientation of the new crust created.
Convection currents are pulling the crust apart.

12. Plate movement

13. Climatic evidence.
Evidence of Ice sheets and glaciers have been found in the tropics. Even during the Earth’s coldest periods it was impossible for ice to be formed there unless these area were once closer to the poles.
Coal has been found in Antarctica. Coal forms in tropical conditions. This means that Antarctica must have been closer to the equator at some stage.

14. Jigsaw fit
Many of the continents fit together almost perfectly like pieces of a Jigsaw. E.g. Africa and South America

15. Geological evidence
Rocks that have exactly the same characteristics have been found thousands of miles away from each other.
Rocks of the same structure and composition have been found in Wales and the East coast of the USA.

16. Plate movement
Plates move by the process of convection. Magma heated at the centre of the earth rises towards the crust. As it hits the crust it spreads out pulling crust with it. The magma then cools sinking towards the centre of the earth where it is heated again.

17. Convection

18. Plate boundaries Constructive Divergent
A Constructive plate boundary is where two plates are pulled apart. A gap appears between the plates letting lava escape. The lava creates new oceanic crust and forms a mid ocean ridge. It forms gentle earthquakes and volcanoes.

19. Constructive
Black smoker
Mid Atlantic Ridge

20. Destructive Plate Boundary
Convergent

21. A destructive plate boundary is where oceanic crust moves towards continental crust. As the oceanic crust is heavier it is forced downwards. This causes extreme pressure which triggers violent earthquakes.

22. Heat produced by friction turns the descending crust back into liquid rock called magma. The hot magma tries to rise to the surface. Where it succeeds there are violent volcanic eruptions

23. Island Arc
Island Arc’s occur when oceanic crust is pushed into another area of oceanic crust. One of the oceanic crusts is subducted beneath the other and melts forming earthquakes and volcanoes. Eg Marianas trench Pacific/Philippines.

24. Collision
Collision plate boundaries occur when the two plates moving together are both continental crust. As continental crust cannot sink or be destroyed then the land between them is buckled and pushed upwards to form high fold mountains.

25. Fold mountains

26. Himalayas
Fold Mountains

33. Conservative
Transform

34. At a conservative plate boundary two plates try to slide slowly past each other. When the two plates stick pressure builds up. When it is finally released it creates severe earthquakes. There are no volcanic eruptions. Eg San Andreas Fault.