FACTORS That determine volcanic erruption 1. Magma’s temperature 2. Magma’s composition 3. Dissolved gasses
M AGMA TYPESComposition Silica content Viscosity Gas Content Tendency to Volcanic form Landforms pyroclasticsBasaltic Least Least Least Least Shield dome, 50% 1-2% Basalt platform, Cinder conesAndesitic Intermediate Intermediate Intermediate Intermediate Composite 60% 3-4% conesRhyolitic Most Greatest Greatest Greatest Volcanic 70% 4.1-6% domes, Pyroclastic flows
M AGMA’ S C OMPOSITION Basaltic Tends to be fluid Can travel a distance of 150km from the crater Andesitic Volcanic roc composition is in between Basaltic and Rhyolitic. Rhyolitic Very viscous Tends to create stream-like ribbon flows
O THER C OMPONENTS Magma’s Temperature High – Fluid magma Low – Viscous magma Dissolved gasses 75% - Water, 15% - Carbon Dioxide, 10% - other gasses Silica Content Poor – More fluid, Gasses can escape easily Rich – Traps gasses which may lead to explosive erruptions
E XTRUDED M ATERIALS Lava Magma without trapped gas Comes from basaltic magma due to low silica content Gasses Pyroclastics High silica content magma that forms from pulverized rock.
C ONTINUATION Ash ~ Formed when lava contains many bubbles Pumice ~ Froth like structure Lapilli ~ Walnut sized Cinder ~ Pea sized Blocks ~ Bigger than lapilli, Made from hardened lava Bombs ~ incandescent (glowing) lava