1. Physicochemical Controls on Eruption Style vs.
Non explosive eruption with effusive lava flow
Explosive eruption with voluminous plume of tephra

2. Eruption style depends on composition of the magma
Eruption style depends on composition of the magma! That is the “chemical” part of the word “physicochemical”. Composition of magma influences: * Viscosity * Temperature * Amount of dissolved gases These three factors refer to the physics of the magma or the “physico” part of the word “physicochemical”.

3. For composition, we refer to magma in terms of the amount of oxygen and silicon OR silica (SiO2) content.
SiO2 Content
Magma Type
Volcanic Rock
~ 50%
Mafic
Basalt
~ 60 %
Intermediate
Andesite
~ 70 %
Felsic
Rhyolite

4. High SiO2 = High viscosity = = Explosive Low SiO2 = Low viscosity = = Non-explosive
Explosiveness
Low/Non-explosive
Intermediate
High/Explosive

5. More on physics of magma:
Dissolved Gases:
Highly viscous magma does not allow gases to escape, also creating an explosive eruption
Temperature:
Low silica rocks melt at lower temperatures. This low temperature magma does not allow gases to escape… AGAIN leading to an explosive eruption

6. Physicochemical Controls on eruption style:
SiO2
Magma Type
Rock Type
Viscosity
Gas Content
Temperature (C)
Eruption Style
Volcano Type
~ 50%
Mafic
Basalt
Low
~ 1100
nonexplosive
Shield
~ 60%
Intermediate
Andesite
~ 1000
intermediate
Stratovolcano
~ 70%
Felsic
Rhyolite
High
~ 800
explosive
Cinder Cone
Main Point:
High Silica = Explosive Eruption
Low Silica = Non-explosive Eruption