- Slides: 6
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! 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 (Si. O 2) content. Si. O 2 Content Magma Type Volcanic Rock ~ 50% Mafic Basalt ~ 60 % Intermediate Andesite ~ 70 % Felsic Rhyolite
High Si. O 2 = High viscosity = = Explosive Low Si. O 2 = Low viscosity = = Non-explosive Viscosity/ Explosiveness Low/Nonexplosive 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: Si. O 2 Magma Type Rock Type Viscosity Gas Content Temperature Eruption (C) Style Basalt Low ~ 1100 nonexplosive Shield ~ 60% Intermediate Andesite Intermediate ~ 1000 intermediate Stratovolcan o ~ 70% Felsic High ~ 800 explosive Cinder Cone ~ 50% Mafic Rhyolite Main Point: High Silica = Explosive Eruption Low Silica = Non-explosive Volcano Type