Module 12 volcanoes

Module 12Module 12

VolcanoesVolcanoes

The gods of volcanoes doing their taskThe gods of volcanoes doing their task

A A volcanovolcano is a is a ventvent or or fissurefissure in the Earth’s crust in the Earth’s crust through which molten magma, hot gases, and through which molten magma, hot gases, and other fluids escape to the surface of the land or to other fluids escape to the surface of the land or to the bottom of the seathe bottom of the sea

Volcanoes may be classified broadly into:Volcanoes may be classified broadly into: Central TypesCentral Types: the products escape via a single : the products escape via a single

pipe (vent)pipe (vent) Fissure TypesFissure Types: the products escape from a : the products escape from a

linear vent or cracklinear vent or crack

VOLCANOESVOLCANOES

Vent positionsVent positions

Central EruptionCentral Eruption

Fissure EruptionFissure Eruption

Side EruptionSide Eruption

Vent positionsVent positions

Earth’s GeothermEarth’s Geotherm

GEOTHERMGEOTHERM: increase in : increase in temperature with depth in the temperature with depth in the earthearth

GEOTHERMAL GRADIENTGEOTHERMAL GRADIENT is is the rate of change of T with the rate of change of T with depthdepth

In upper 100 km, average In upper 100 km, average geothermal gradient = 30geothermal gradient = 3000C C kmkm-1-1

Heat source is decay of Heat source is decay of radioactive elementsradioactive elements

This heat causes melting of This heat causes melting of rocks to form Magmarocks to form Magma

Composition of MagmaComposition of Magma

Variation in magma properties include:Variation in magma properties include: SILICA CONTENTSILICA CONTENT

varies from 45% to 75% varies from 45% to 75% VOLATILES (GAS CONTENT)VOLATILES (GAS CONTENT)

most common gases: H most common gases: H22O vapor,O vapor, CO CO22, SO, SO22, H, H22SS

TEMPERATURE OF ERUPTED MAGMATEMPERATURE OF ERUPTED MAGMA varies from 1200 varies from 120000C to about 800C to about 80000CC

Variation in magma properties affect Variation in magma properties affect VISCOSITYVISCOSITY of of the magmathe magma

VISCOSITYVISCOSITY refers to the thickness or fluidity of a refers to the thickness or fluidity of a liquidliquid Liquid with HIGH viscosity are very thick, Liquid with HIGH viscosity are very thick,

stickysticky Liquid with LOW viscosity are very fluidLiquid with LOW viscosity are very fluid

Effect of various properties on magma viscosity:Effect of various properties on magma viscosity: TemperatureTemperature: HIGH temperature = LOW : HIGH temperature = LOW

viscosity (viscosity (i.e.i.e. very fluid) very fluid) Silica ContentSilica Content: HIGH silica = HIGH viscosity: HIGH silica = HIGH viscosity Volatile ContentVolatile Content: HIGH volatiles = LOW : HIGH volatiles = LOW

viscosityviscosity

(However, (However, high gas contentshigh gas contents contribute to contribute to explosiveexplosive eruptions) eruptions)

Viscosity of MagmaViscosity of Magma

Types of VolcanoesTypes of Volcanoes

Types of VolcanoesTypes of Volcanoes

Shield VolcanoesShield Volcanoes

Shield VolcanoesShield Volcanoes

Shield VolcanoesShield Volcanoes

Shield VolcanoesShield Volcanoes

Shield VolcanoesShield Volcanoes

Shield VolcanoesShield Volcanoes

HOT SPOT

Shield VolcanoesShield Volcanoes

Cinder Cone VolcanoesCinder Cone Volcanoes

Cinder Cone VolcanoesCinder Cone Volcanoes

Strato VolcanoesStrato Volcanoes

Strato VolcanoesStrato Volcanoes

Strato VolcanoesStrato Volcanoes

Strato VolcanoesStrato Volcanoes

Strato VolcanoesStrato Volcanoes

Strato VolcanoesStrato Volcanoes

Lava Dome VolcanoesLava Dome Volcanoes

Dome VolcanoesDome Volcanoes

Caldera VolcanoesCaldera Volcanoes

The formation of The formation of CalderaCaldera

Caldera VolcanoesCaldera Volcanoes

Eruption TypesEruption Types

HAWAIIAN-HAWAI

Eruption TypesEruption Types

STROMBOLIAN - ANAK KRAKATAU

Eruption TypesEruption Types

VULCANIAN DOME - MERAPI

Eruption TypesEruption Types

VULCANIAN - SURTSEYAN

Eruption TypesEruption Types

VULCANIAN - PAPANDAYANGAMALAMA

Eruption TypesEruption Types

PELEEAN - ST HELLENS

Eruption TypesEruption Types

PLINIAN PINATUBO

Eruption TypesEruption Types

PLINIAN - TAMBORA

Eruption TypesEruption Types

Global Distribution of VolcanoesGlobal Distribution of Volcanoes

Most Most subduction zones are in the “Ring of Fire” (so-calledsubduction zones are in the “Ring of Fire” (so-called because of volcanism of the Pacificbecause of volcanism of the Pacific))

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Distribution of VolcanoesDistribution of Volcanoes

Volcanism & Plate TectonicsVolcanism & Plate Tectonics

Volcanism in continentalVolcanism in continental

Volcanism in islands arcVolcanism in islands arc

Pacific Ocean

Volcanism & Plate TectonicsVolcanism & Plate Tectonics

Volcanism in Volcanism in Mid Oceanic RidgeMid Oceanic Ridge

Volcanism & Plate TectonicsVolcanism & Plate Tectonics

Hot Spot VolcanismHot Spot Volcanism

Classification of Volcanic EnvironmentClassification of Volcanic Environment

Types and Zones of VolcanismTypes and Zones of Volcanism

VOLCANIC NECK

COLUMNAR JOINT

Finally . . . Finally . . . Rest in PeaceRest in Peace

Major Volcanoes of IndonesiaMajor Volcanoes of Indonesia(with eruptions since 1900 A.D.)(with eruptions since 1900 A.D.)

Distribution of Magmatic Arcs of IndonesiaDistribution of Magmatic Arcs of Indonesia(source: Carlile & Michell, 1994)(source: Carlile & Michell, 1994)