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Natural Hazard

What is natural hazard ?

It is a naturally occurring event . Threatens human lives . Causes damage to property .

What is the internal structure of the earth ?

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Natural process Natural hazards Tectonic 1. Earthquakes

2. volcanic eruptions 3. Tsunamis

Climate -related 1. Drought 2. Floods 3. Tropical cyclones

Core

It is the central part of the earth. Composed mostly of iron and nickel . Core is divided into inner core and outer core . Approximately 1,200 kilometres thick. (inner core) Inner core is solid due to the extreme pressure exerted on it by

the surrounding layers. Outer core is a liquid layer approximately 2,100 kilometres thick. (temperature is estimated to be 3000degree and 5000degree)

Mantle lies above the core . occupying 80 per cent of the earth's total volume. Mantle is 2900 kilometres thick Made up mostly of solid rock that flows under high

temperature and pressure . Mantle divided into upper mantle and lower mantle. temperature of mantle ranges between 800degree and

3000degree. upper mantle consists of a layer of solid rock and the

asthenosphere.

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Crust Crust is the earth's outermost layer on which we live. It makes up less than 1 per cent of the earth's volume . Crust beneath the oceans is called oceanic crust . Crust beneath the continents is known as continental crust . Crust can range in thickness from a few kilometres to more than

70kilometres. Crust , together with the uppermost mantle , is referred to as

the lithosphere. When the rocks in the lithsophere melt, hot molten rock known

as magma is formed .

Type of crust Location Thickness Type and age of rock Oceanic crust Beneath deep oceans Between 5

and 8 km Consists a heavy and

dense rock . Rock of less than 200

million years old.Continental crust Beneath the earth's

continental land masses and under shallow seas close to continents

Between 30 and 60km

Consists of lighter rock. rock ages from very

recent to nearly 4 billion years old

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What do tectonic plates move ?

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This causes plates to be dragged along and to move away from each other.

convection currents are movement of heat within the mantle. Material in the mantle is heated by the core, causing the mantle material to expand, rise and spread out beneath the plates

Then, the hot mantle material cools slightly and sinks , pulling the plates along.

sinking mantle material heats up again as it nears the core ,the whole process repeats.

Slab- pull force occurs when a denser oceanic plate is forced beneath a less dense continental plates or oceanic plate in a process called subduction.

As the plate subducts , it pulls the rest of the plate along .The subducting plates drives the downward-moving portion of convection currents.

mantle material which is found away from where the plates subduct drives the rising portion of convection

What are the different types of plate boundaries ?

Arrow stand for example of plates.

What are the types of plates movement ?

1. Divergent (where plates move away from each other)2. Convergent (where plates move towards each other)3. Transform (where plates move past each other)

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Oceanic -Oceanic Plate Divergence

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2.Magma rises at the zone of divergence to create a ridge of new oceanic floor known as a mid -oceanic ridge.

3. At various points along the mid oceanic ridge , magma builds up above sea level to formed volcanoes . These volcanoes are known as volcanic island . Example is the north Atlantic ocean is the Azores .

When two oceanic plates diverge, a mid-oceanic ridge is formed. An example is the Mid-Atlantic Ridge in the middle of the Atlantic Ocean, which was formed when the North American

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1. when two oceanic plate diverge fractures are formed at the plate boundary.

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