AQA A2 Geography Plate Tectonics: Types of Lava

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Types of Lava
Lava is hot melted rock found when a volcano is erupting.
There are three main types of lava: basaltic, andesitic and Rhyolitic.
Basaltic Lava
Basaltic lavas originate largely from the upward movement of mantle material.
They are found at constructive plate margins.
They are most common along spreading ridges but are also found at hot spots and within more developed
rift systems.
It has less gas in it as most of it escapes easily.
It is less viscous which means it can flow faster and further.
As a result, eruptions of basaltic lava usually aren't violent.
Andesitic Lava
Andesitic lavas are typical of destructive plate margins.
They have higher viscosities and so they flow less easily.
Volcanic gases cannot escape easily from andesitic lava.
They often form blockages in volcanic vents and pressure builds up until it is released as a violent eruption.
Rhyolitic Lava
Rhyolitic lavas are most often found at destructive and collision margins.
They are very thick and viscous and so very slow flowing.
Large amounts of gas are trapped in this lava and as a result form very explosive volcanoes.
When the rhyolite lava cools it forms a black glassy lava field.
Basaltic Lava Andesitic Lava Rhyolitic Lava
Silica content
Low Medium High
Viscosity Low (runny) Medium High (thick)
Temperature of
Over 950oC 750-950oC Less than 750 oC

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Types of Lava Flow
There are three types of lava flows: A'a, Pahoehoe and Pillow.
A'a lava flows have a rough surface made up of broken blocks of lava.
It is much thicker lava and so very viscous.
Pahoehoe lava is usually the first kind of lava to erupt out of a
The lava has a low viscosity and so flows easily.
It has a smooth surface that cools quickly and becomes thicker
and so flows more slowly.…read more


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