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

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”.

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

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

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

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