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VOLCANOESVOLCANOES

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 ↑


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