V OLCANOES Weak spots in the crust where magma (molten material) comes up to the surface. Most are found over the subduction zones. The word volcano comes from the Roman god of fire, Vulcan.
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
V OLCANO T YPES
S HIELD Built from Basaltic magma Broad dome shape Example Mauna Loa
C INDER C ONE Very steep, small (300m) Made from pyroclastics Collapses easily
C OMPOSITE Large, nearly symmetrical Made up of interbedded layers of lava and pyroclasts Examples Mt. Mayon Mt. St. Hellens