Types of Lava
Extreme Earth Events - 12ESS
2024
Lava Flows & Eruptions
- How explosive a volcanic eruption is, and how far the lava will travel depends on the viscosity
- Viscosity: A measure of how
liquid/or not the material is
- High viscosity –> thick, molassas-like substance
- Low viscosity –> like water
Silica Content
- Silica is a silicon-oxygen compound found in rock.
- It has the greatest effect on lava viscosity.
- High silica content –> high viscosity.
- The particles are more tightly bound, this means it moves slower and is more explosive.
Gas Content
- Typically water, carbon dioxide, sulfur dioxide
- Gas can be compressed into a liquid (like soda), under the Earth
- As the magma rises and the pressure is released, the gas will try escape the magma (highly explosive)
- Magma with high gas content is not very viscous, but becomes more viscous as the gas escapes
Water Content
- Water is introduced through subduction of oceanic plates into the mantle
- Higher water content –> lower viscosity
- Think of this as diluting honey with water
Temperature
- Hot –> higher viscosity
- Magma composed of melted crust has a lower temperature
- Magma composed of melted mantle rocks has a higher temperature
Basaltic
- Lower silica content
- Typically less than 52%
- Often found at divergent plate boundaries/hot spots
- Less viscous lava/less explosive eruptions
- Fissure/dome volcanoes
Andesitic
- Dark grey rock
- 52-66% silica
- Often found at subduction zones without rising to the surface
- Medium viscosity/medium explositive
- Stratovolcanoes
Rhyolitic
- Typically higher than 66% silica content
- Grey/pink in colour
- Found at convergent boundaries where subducted crust then rises to the surface
- Strato/composite volcanoes
