Unit 1B Natural hazards

Today What is a natural hazard? List them. What is the Earth’s structure? What are tectonic plates? How is the Earth changing? How are they linked to volcanoes and earthquakes?

All natural hazards – can you get what they show?

The Structure of the Earth A thin crust - 10-100km thick and not very dense A mantle – extends almost halfway to the centre, hot and dense A core – made of molten nickel and iron. Outer part is liquid and inner part is solid. Gets hot due to radioactive decay. The Earth is believed to be 4500 million years old

The structure of the earth The inner core is in the centre of the earth and is the hottest part of the earth. The inner core is solid. It is made up of iron and nickel with temperatures of up to 5500°C. With its immense heat energy, the inner core is like the engine room of the Earth. The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot here, with temperatures similar to the inner core.

The structure of the earth The mantle is the widest section of the earth. It has a diameter of approximately 2900km. The mantle is made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but lower down, nearer the inner core, the rock is soft and beginning to melt. The crust is the outer layer of the earth. It is a thin layer between 0-60km thick. The crust is the solid rock layer upon which

Plates and plate boundaries The earth's crust is broken up into pieces. These pieces are called plates. Heat rising and falling inside the mantle creates convection currents. The convection currents move the plates. The movement of the plates, and the activity inside the earth, is called plate tectonics. Plate tectonics cause earthquakes and volcanoes. The point where two plates meet is called a plate boundary. Earthquakes and volcanoes are most likely to occur either on or near plate boundaries.

These plates either: Diverge – move towards each other or Transform – move past each other Converge – move towards each other What happens at the plate margins varies: 1. If the plates are diverging, then the plate boundaries move apart and new crust is created by the mantle welling up from below . This a constructive margin. 2. If the plates are moving past each other, then the margin is a conservative margin, as crust is neither made nor destroyed. 3. If the plates are moving towards each other, then one of 2 things can happen a) One plate moves under the other. This is a destructive margin (as some crust is reabsorbed into the mantle and destroyed) b) If two plates approach head on and fold up at the edges, this is a collision (zone) margin.

Don’t worry about the names of the plates – you do not need to know them! But take a few minutes to colour in examples of each type on your grey map.

Now a bit more about each plate – what is this one? The 2 plates move apart and molten rock or magma rises up to fill the gap and forms new crust. E.g. the mid- Atlantic Ridge, which Iceland forms part of – it moves about 3cm a year In 1967, there were undersea eruptions off Iceland – soon an island grew out of the sea - named Surtsey which is now 2.8km2 and 178m above Sea Level. As you see, volcanoes occur but so does the odd gentle earthquake.

Which is this? No diagram for this type of plate margin – they just slide past each other! As you see, this is a map of the famous San Andreas Fault on the West Coast of California. As the rock on either side is pressing so hard together, as the 2 plates pass, they judder – an earthquake. In 1906, some parts of the plate moved 6m! But you will not find volcanoes along these plates!

What is this called? These are usually found where an continental (land) crust is approaching an oceanic crust – the land crust is less dense and so floats over the oceanic crust which is forced down into the magma where it melts. This is called a subduction zone. Sometimes the edge of the continental crust is forced up at the edge by displaced magma which then escapes through volcanoes. So earthquakes and volcanoes here! The Andes Mountains were formed this way, along with the volcanoes, Chimborozo and Cotopaxi

No Volcanoes here either The last one? Here 2 continental plates collide – neither plate can sink or be destroyed so fold mountains are formed. The Himalayas are growing at 5cm a year! And the Alps were an older version, but they have stopped growing now. No Volcanoes here either

If the plates are moving, were the continents always where we see them today? No and there is lots of evidence for this The process is called continental drift Evidence for this: Mountain chains match up Fossils match up The continents fit together like a jigsaw (not perfect because of erosion!)

Continental Drift

Continental Drift

Continental Drift

Continental Drift

Can you see the UK, North America Can you see the UK, North America? Each colour represents a rock type – see how they fit together

Homework Make sure you can explain, understand and give examples of the following terms – to do this, fill in the table on the worksheet and label an earth structure diagram: collision margin. conservative margin converge core destructive margin diverge earthquake mantle. plate boundary tectonic plate transform