Transcript Y10Ge U1B_1 Hazards Oct 15 PP

Unit 1B Natural hazards
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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?
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All natural hazards – can
you get what they show?
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A thin crust - 10100km thick and
not very dense
The Structure of the
Earth
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
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The structure of the earth
• The inner core is in the centre of the earth
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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.
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The structure of the earth
• The mantle is the widest section of the earth.
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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
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Plates and plate boundaries
• The earth's crust is
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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.
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• These plates either:
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 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.
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• 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.
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Now a bit more about each plate – what
is this one?
• The 2 plates move apart and
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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.
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Which is this?
• No diagram for this
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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!
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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.
The Andes Mountains
• So earthquakes and volcanoes were formed this way,
here!
along with the volcanoes,
Chimborozo and Cotopaxi
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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
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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:
1. Mountain chains match up
2.Fossils match up
3.The continents fit together like a jigsaw
(not perfect because of erosion!)
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Continental Drift
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Continental Drift
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Continental Drift
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Continental Drift
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Can you see the UK, North America?
Each colour represents a rock type – see how
they fit together
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Homework
• Make sure you can explain, understand and give examples
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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
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