Physical Geography notes

Section A - Restless Earth
The earth’s structure
At the centre of the earth is the core. Surrounding that is a mass of molten rock called the mantle. The thin layer on the outside is called the crust. There are two types of crust, continental and oceanic. The crust is made up of seven major plates and many smaller ones. The plates move due to convection currents rising in the mantle.

Distribution of earthquakes and volcanoes
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Mainly found along plate boundaries.
In linear clusters (lines).
At destructive boundaries.
Around the Pacific plate or ‘Ring of Fire’
West Coast of America’s
No volcanoes on conservative boundaries
Volcanoes also found in the middle of plates or ‘Hot spots’.

Types of plate boundary
Destructive

Constructive

Conservative/Transform

Moving towards each other
Oceanic crust is destroyed in subduction zone
Fold mountains
Deep sea trench
Composite Volcanoes
Severe Earthquakes
e.g. West coast of S. America

Moving apart
New crust is formed as the gap is filled by magma
Shield volcanoes
Volcanic islands e.g. Iceland
Under oceans
e.g. Mid-Atlantic ridge

Moving past each other
Either opposite directions or same at different speeds
Severe earthquakes
No volcanoes
Crust can be crumpled
e.g. San Andreas fault

Volcanoes
Volcanoes form where magma escapes through gaps in the crust.
Mostly found at Destructive and constructive plate boundaries.
Also at hot spots in the middle of plates e.g. Hawaii
Key terms :
Crater – The opening at the top of the volcano
Vent – The pipe that takes magma up to the crater
Magma Chamber – Underground chamber where magma is stored
Volcanic bombs – Large, hot boulders thrown from the volcano
Secondary cone – Smaller cone on the side of the main cone

Shield volcano

Composite volcano

Wide, gentle slopes
Constructive boundaries
Frequent eruptions
Runny lava
Not very violent
e.g. Mauna Loa, Hawaii or some on Iceland

Tall, steep