VOLCANOES. TYPES OF VOLCANOES Volcanoes are classified by appearance Steep slopes = Strato/composite Volcanoes Gentle slopes = Shield volcano Appearance

VOLCANOES

TYPES OF VOLCANOES Volcanoes are classified by appearance Steep slopes = Strato/composite Volcanoes Gentle slopes = Shield volcano Appearance predicts type of eruption Steep slopes explosive (violent) eruptionsexplosive (violent) eruptions Gentle slopes non-violent (quiet) eruptionsnon-violent (quiet) eruptions

TYPES OF ERUPTIONS ERUPTIONS FALL INTO 2 CATEGORIES Violent (explosive) eruptions destroy the volcano Non-Violent (calm or quiet) eruptions build up the volcano

STRATO/COMPOSITE VOLCANOES Steep slopes Explosive Formed from viscous (thick) lava Found in subduction zones & some hot spots Ex/: Casades, Mt St Helens, 2, 3CasadesMt St Helens23 Formed from viscous (thick) lava Found in subduction zones & some hot spots Ex/: Casades, Mt St Helens, 2, 3CasadesMt St Helens23

SHIELD VOLCANO Gentle slopes- Non-violent Formed from fluid (thin) lava Only found over a hot spots Ex: Hawaiian islandsHawaiian islands Formed from fluid (thin) lava Only found over a hot spots Ex: Hawaiian islandsHawaiian islands

MAGMA/LAVA ERUPTIONS Non-Explosive Eruptions: Fluid lava flows easily allows gases to bubble away Explosive Eruptions: Viscous lava traps the gases until large pressures build up & the system explodes Pyroclastic flow (ash, rock fragments) flow out of vent

ERUPTION HAZARDS LAHAR Water, mud & ash that flow like a river

EXPLOSIVE HAZARDS PYROCLASTIC FLOW Travels over 200 mph Tephra = all ash & rock fragments ash: pieces smaller than 2 mm; travel farthest lapelli: small pieces between 2-66 mm volcanic bomb: pieces larger than 64 mm Burns EVERYTHING in its path

EXPLOSIVE HAZARDS VISCOUS LAVA (High Viscosity) Cool temperature Compositon: silica-rich (granitic) Thick & gooey Erupt violently; scattering ash and fragments widely Does not flow very far; builds steep-sides; often destroys volcanoes Ex. rhyolithic & andesitic lava strato volcanoes

NON-EXPLOSIVE HAZARD FLUID LAVA (Low viscosity) Higher temperatures Composition: Low silica (basaltic) Thin Erupt quietly Great flows of lava that build mountains Ex. Basaltic lava shield volcanoes FLUID LAVA (Low viscosity) Higher temperatures Composition: Low silica (basaltic) Thin Erupt quietly Great flows of lava that build mountains Ex. Basaltic lava shield volcanoes

VISCOSITY MAGMA/LAVA Viscosity is resistance to flow Viscosity determined by Temperature HOT= thin, flows easily COOL= thick Composition Silica(SiO 2 )=mineral in magma LOW SILICA (basalt) = thin HIGH SILICA (granite) = thick low gas = flows easily

WHAT KIND OF LAVA FLOW? Viscous lava thick (granitic high silica content) traps gas violent eruptions destroys mountains Fluid lava thin ; flows far; allows gas to escape; quiet(non-violent) eruptions builds mountain Low Viscosity lava Flows great distances

FORMATION ERUPTIONS Volcanoes are formed by 1.SUBDUCTION explosive eruptionsSUBDUCTION 2.Sea Floor Spreading quiet eruptions 3.Hot Spots usually quiet eruptions

VOLCANO FORMATION: HOT SPOTS A fixed source of magma rising beneath a plate forming volcanic islands Magma can be basaltic or granitic so eruptions can be explosive or quiet A fixed source of magma rising beneath a plate forming volcanic islands Magma can be basaltic or granitic so eruptions can be explosive or quiet

PREDICTING ERUPTIONS: VOLCANO MONITORING Predict Eruptions by Study and comparison of past eruptions Warning Signs- Small quakes (seismicity) Swelling of slopes Changes in water pH Changes in gases emitted

VOLCANO SUMMARY APPEARANCE ERUPTIONS Steep slopes (Strato volcano) explosive (violent) Gentle slopes (Shield volcano) non-explosive (quiet) MAGMA VISCOSITY ERUPTIONS Viscous (thick) magma explosive (violent - Strato) Fluid (thin) magma non-explosive (quiet - Shield) FORMATION MAGMA/LAVA ERUPTIONS Subduction zones explosive (violent - Strato) Sea Floor spreading zones non-explosive (quiet- shield) Hot spot usually non-explosive, but can be explosive MONITORINGPREDICTION OF ERUPTIONS Slope changes, quakes , water pH , gases APPEARANCE ERUPTIONS Steep slopes (Strato volcano) explosive (violent) Gentle slopes (Shield volcano) non-explosive (quiet) MAGMA VISCOSITY ERUPTIONS Viscous (thick) magma explosive (violent - Strato) Fluid (thin) magma non-explosive (quiet - Shield) FORMATION MAGMA/LAVA ERUPTIONS Subduction zones explosive (violent - Strato) Sea Floor spreading zones non-explosive (quiet- shield) Hot spot usually non-explosive, but can be explosive MONITORINGPREDICTION OF ERUPTIONS Slope changes, quakes , water pH , gases

VOLCANOES. TYPES OF VOLCANOES Volcanoes are classified by appearance Steep slopes = Strato/composite Volcanoes Gentle slopes = Shield volcano Appearance

viscous thick lava

volcano slide

great flows of lava

mountains fluid lava

formation eruptions

kind of lava flow

mountain low viscosity

quietnonviolent eruptions

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