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Three Types of Volcanoes
1. List and describe the three types of volcanoes.
EXPLOSIVE HAZARDS VISCOUS LAVA (High Viscosity)
Cool temperature
Composition: 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→ stratovolcanoes
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
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
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
ERUPTION HAZARDS LAHAR Water, mud & ash that flow like a river
Shield Volcanoes • The magma inside a shield volcano is rich in iron and magnesium and is very fluid. • Since the magma is very fluid, the lava coming out of the volcano tends to flow great distances. • When shield volcanoes erupt, the flowing lava gives the volcano the shape of a gently sloping mountain.
Shield Volcanoes Eruptions of shield volcanoes are mild and can occur several times. Mauna Loa in Hawaii is an example of a shield volcano.
Shield Volcanoes Low silica level Low viscosity Lava High or low levels of gas Low to medium explosivity Flattened mound Resembles a warrior’s shield
Mauna Loa, Hawaii
Piton de la Fournaise
Surtsey, Finland
Composite Volcanoes • The magma inside a composite volcano is rich in silica and much thicker than magma from a shield volcano. • Gases get trapped inside this thicker magma. • Eruptions from composite volcanoes can be flowing lava or explosions. The explosive eruptions come from the trapped gases and produce cinders and ash.
Composite Volcanoes • These different types of eruptions are what give composite volcanoes their alternating layers of lava and cinders. • Composite volcanoes have much steeper slopes than shield volcanoes. • Mount Fuji in Japan and Mount St. Helens in the USA are examples of composite volcanoes.
Composite Volcanoes High in silica High viscosity magma High levels of gas Highly explosive Cone shaped Formed by layers of lava flow and ash buildup
Mt. Rainier, Washington
Mt. Fuji, Japan
Mt. St. Helens, Washington
Cinder Cone Volcanoes • The magma inside a cinder cone volcano has large amounts of gas trapped in it. • Eruptions from cinder cone volcanoes are violent and explosive because of all the gas trapped in the magma. • The large amounts of hot ash and lava thrown out of the vent fall to the ground forming the cone shape that these volcanoes have.
Cinder Cone Volcanoes • Cinder cone volcanoes are usually only active for a short time and then become dormant (inactive). • Paricutin in Mexico is an example of a cinder cone volcano.
Cinder cones Low silica lava High levels of gas “Fire-fountain” eruptions Commonly found on the flanks of shield volcanoes Made from a pile of rock pieces Structurally weak
Pu'u ka Pele, Hawaii (on the flanks of Mauna Loa)
Floreana Island, Galapagos
Puu OO, Hawaii
2. Explain how volcanoes relate to plate tectonics.
WHAT KIND OF LAVA FLOW? Fluid lava • • • •
Fluid lava Flows great distances
thin ; flows far; allows gas to escape; quiet(non-violent) eruptions builds mountain
Viscous lava • • • •
thick (granitic – high silica content) traps gas violent eruptions destroys mountains
FORMATION →ERUPTIONS Volcanoes are formed by 1. SUBDUCTION explosive eruptions 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”
1. List and describe the three types of volcanoes.
EXPLOSIVE HAZARDS VISCOUS LAVA (High Viscosity)
Cool temperature
Composition: 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→ stratovolcanoes
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
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
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
ERUPTION HAZARDS LAHAR Water, mud & ash that flow like a river
Shield Volcanoes • The magma inside a shield volcano is rich in iron and magnesium and is very fluid. • Since the magma is very fluid, the lava coming out of the volcano tends to flow great distances. • When shield volcanoes erupt, the flowing lava gives the volcano the shape of a gently sloping mountain.
Shield Volcanoes Eruptions of shield volcanoes are mild and can occur several times. Mauna Loa in Hawaii is an example of a shield volcano.
Shield Volcanoes Low silica level Low viscosity Lava High or low levels of gas Low to medium explosivity Flattened mound Resembles a warrior’s shield
Mauna Loa, Hawaii
Piton de la Fournaise
Surtsey, Finland
Composite Volcanoes • The magma inside a composite volcano is rich in silica and much thicker than magma from a shield volcano. • Gases get trapped inside this thicker magma. • Eruptions from composite volcanoes can be flowing lava or explosions. The explosive eruptions come from the trapped gases and produce cinders and ash.
Composite Volcanoes • These different types of eruptions are what give composite volcanoes their alternating layers of lava and cinders. • Composite volcanoes have much steeper slopes than shield volcanoes. • Mount Fuji in Japan and Mount St. Helens in the USA are examples of composite volcanoes.
Composite Volcanoes High in silica High viscosity magma High levels of gas Highly explosive Cone shaped Formed by layers of lava flow and ash buildup
Mt. Rainier, Washington
Mt. Fuji, Japan
Mt. St. Helens, Washington
Cinder Cone Volcanoes • The magma inside a cinder cone volcano has large amounts of gas trapped in it. • Eruptions from cinder cone volcanoes are violent and explosive because of all the gas trapped in the magma. • The large amounts of hot ash and lava thrown out of the vent fall to the ground forming the cone shape that these volcanoes have.
Cinder Cone Volcanoes • Cinder cone volcanoes are usually only active for a short time and then become dormant (inactive). • Paricutin in Mexico is an example of a cinder cone volcano.
Cinder cones Low silica lava High levels of gas “Fire-fountain” eruptions Commonly found on the flanks of shield volcanoes Made from a pile of rock pieces Structurally weak
Pu'u ka Pele, Hawaii (on the flanks of Mauna Loa)
Floreana Island, Galapagos
Puu OO, Hawaii
2. Explain how volcanoes relate to plate tectonics.
WHAT KIND OF LAVA FLOW? Fluid lava • • • •
Fluid lava Flows great distances
thin ; flows far; allows gas to escape; quiet(non-violent) eruptions builds mountain
Viscous lava • • • •
thick (granitic – high silica content) traps gas violent eruptions destroys mountains
FORMATION →ERUPTIONS Volcanoes are formed by 1. SUBDUCTION explosive eruptions 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”
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