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
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
Moving towards each other
Oceanic crust is destroyed in subduction zone
Deep sea trench
e.g. West coast of S. America
New crust is formed as the gap is filled by magma
Volcanic islands e.g. Iceland
e.g. Mid-Atlantic ridge
Moving past each other
Either opposite directions or same at different speeds
Crust can be crumpled
e.g. San Andreas fault
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
Wide, gentle slopes
Not very violent
e.g. Mauna Loa, Hawaii or some on Iceland