TYPES OF VOLCANOESTYPES 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) eruptions
• Gentle slopes → non-violent (quiet) eruptions
TYPES OF ERUPTIONSTYPES OF ERUPTIONSERUPTIONS 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 STRATO/COMPOSITE VOLCANOES Steep slopes – Explosive
Formed from viscous (thick) lava Found in subduction zones & some hot
spotsEx/: Casades, Mt St Helens, 2, 3
Formed from viscous (thick) lava Found in subduction zones & some hot
spotsEx/: Casades, Mt St Helens, 2, 3
SHIELD VOLCANO Gentle slopes- Non-violentSHIELD VOLCANO Gentle slopes- Non-violent Formed from fluid (thin) lava Only found over a hot
spots Ex: Hawaiian islands
Formed from fluid (thin) lava Only found over a hot
spots Ex: Hawaiian islands
MAGMA/LAVA →ERUPTIONSMAGMA/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 ERUPTION HAZARDSLAHAR Water, mud &
ash that flow like a river
LAHAR Water, mud &
ash that flow like a river
EXPLOSIVE HAZARDS EXPLOSIVE HAZARDSPYROCLASTIC 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
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 EXPLOSIVE HAZARDSVISCOUS 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
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 HAZARDNON-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/LAVAVISCOSITY→MAGMA/LAVA
Viscosity is resistance to flow
Viscosity determined byTemperature HOT= thin, flows easily COOL= thick
Composition Silica(SiO2)=mineral in magmaLOW SILICA (basalt) = thinHIGH SILICA (granite) = thicklow gas = flows easily
WHAT KIND OF LAVA FLOW?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 →ERUPTIONSFORMATION →ERUPTIONS
Volcanoes are formed by
1. SUBDUCTION explosive eruptions
2. Sea Floor Spreading quiet eruptions
3. Hot Spotsusually quiet eruptions
VOLCANO FORMATION: HOT SPOTSVOLCANO 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 MONITORINGPREDICTING 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 SUMMARYVOLCANO SUMMARYAPPEARANCE → 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
MONITORING→PREDICTION 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
MONITORING→PREDICTION OF ERUPTIONS Slope changes, quakes↑, water pH↓ , gases ↑