VolcanoesVolcanoesand Plate Tectonicsand Plate Tectonics (part 1) (part 1)

““an opening in the Earth’s crust an opening in the Earth’s crust through which an eruption takes through which an eruption takes

place”place”

VolcanoesVolcanoes (cont.) (cont.)

Nature of a volcanic eruption Nature of a volcanic eruption depends on the depends on the MagmaMagma

Magma – hot, liquid rock Magma – hot, liquid rock beneathbeneath the the Earth’s surface.Earth’s surface.

Lava – hot, liquid rock that Lava – hot, liquid rock that reachesreaches (and goes (and goes aboveabove) the Earth’s surface.) the Earth’s surface.

VolcanoesVolcanoes (cont.) (cont.) Possible sources of heat below the Possible sources of heat below the

surface:surface: Radioactive decayRadioactive decay is a breaking apart of is a breaking apart of

the nucleus of an atom; as a nucleus the nucleus of an atom; as a nucleus breaks apart, it releases energy which is breaks apart, it releases energy which is changed into heat.changed into heat.

Original HeatOriginal Heat inside the earth may have inside the earth may have been trapped when the earth first formed.been trapped when the earth first formed.

FrictionFriction – results from the movement of – results from the movement of lithospheric plates.lithospheric plates.

Fusion in the coreFusion in the core – nuclear fusion, – nuclear fusion, similar to the sun, is occurring in the coresimilar to the sun, is occurring in the core

VolcanoesVolcanoes (cont.) (cont.)

Active VolcanoActive Volcano – 1300 volcanoes on – 1300 volcanoes on land around the world are thought to land around the world are thought to be active, have erupted within the last be active, have erupted within the last few hundred years.few hundred years.

Dormant VolcanoDormant Volcano – ‘sleeping’ volcano, – ‘sleeping’ volcano, but capable of being activatedbut capable of being activated

Extinct VolcanoExtinct Volcano – has not erupted for – has not erupted for the last several thousand years.the last several thousand years.

VolcanoesVolcanoes (cont.) (cont.)Types of volcanoesTypes of volcanoes

Types of volcanoes are determined by Types of volcanoes are determined by the strength and explosiveness of the the strength and explosiveness of the

eruptioneruption

EruptionEruption Depends on Depends on – a) temperature, a) temperature, – b) composition, and b) composition, and – c) amount of dissolved gases these affect c) amount of dissolved gases these affect

the magma’s viscosity (ability to flow – the magma’s viscosity (ability to flow – more viscous –greater resistance to flow)more viscous –greater resistance to flow)

VolcanoesVolcanoes (cont.) (cont.)

TemperatureTemperature – the hotter-– the hotter-the runnier the runnier (less viscous)(less viscous)……

VolcanoesVolcanoes (cont.) (cont.)

Composition – movement of magma Composition – movement of magma depends on the amount of silica depends on the amount of silica

the the more silicamore silica the greater the the greater the viscosity.viscosity.Felsic - High silica – Felsic - High silica – graniticgranitic – 70% silica – 70% silicaMafic - Low silica – Mafic - Low silica – basalticbasaltic – 30% silica; – 30% silica;

(molecular silica links to make long (molecular silica links to make long chains, even before crystallization chains, even before crystallization begins)begins)

VolcanoesVolcanoes (cont.) (cont.)

Dissolved gasesDissolved gases – this provides the force of an – this provides the force of an eruption. eruption.

As magma moves closer to the surface (like in a As magma moves closer to the surface (like in a volcano) the pressure is reduced and the volcano) the pressure is reduced and the dissolved gases are released – sometimes dissolved gases are released – sometimes suddenly i.e. Soda bottle suddenly i.e. Soda bottle

Gases are: Gases are: water vaporwater vapor Carbon Carbon

Dioxide (CODioxide (CO22))Sulfur Sulfur Carbon Monoxide Carbon Monoxide

(CO)(CO) Sulfur Dioxide, SOSulfur Dioxide, SO22 Hydrogen Sulfide, Hydrogen Sulfide,

HH22S S

VolcanoesVolcanoes (lava) (lava) Felsic – Felsic –

high silicahigh silica

Flows slowly, Flows slowly, gas held gas held within; within; does NOT does NOT allow allow gasses to gasses to escape escape readily –readily –

EXPLOSIVEEXPLOSIVE

VolcanoesVolcanoes (cont.) (cont.) Mafic – low silica; more fluid, DOES allow Mafic – low silica; more fluid, DOES allow

gasses to escape readily – NON-Explosivegasses to escape readily – NON-Explosive

VolcanoesVolcanoes (cont.) (cont.)

………….. In short….. In short…

LavaLava (magma that reaches the (magma that reaches the surface)surface)

FelsicFelsic - flow slowly, gas is held - flow slowly, gas is held within – explosivewithin – explosive

MaficMafic - more fluid, gas easily - more fluid, gas easily escapes – lava pours out slowlyescapes – lava pours out slowly

VolcanoesVolcanoes (cont.) (cont.)

Lava type Felsic Mafic

Silica % High Low

Viscosity High (thick) Low (thin)

Color Light Dark

Rate of movement Slow Quick

Dissolved gasses Cannot easily escape Escapes easily

Nature of eruption Explosive Quiet

Eruptive FragmentsEruptive FragmentsPyroclastic

Tephra: lava that is blasted into the Tephra: lava that is blasted into the air by violent volcanic eruptions and air by violent volcanic eruptions and solidifies as it falls to the ground as solidifies as it falls to the ground as ash, lapilli, ash, lapilli, cinderscinders, blocks, and , blocks, and volcanic bombsvolcanic bombs– Ash – less than 2mm diameterAsh – less than 2mm diameter– Lapilli (also Lapilli (also cinderscinders) – up to 64 mm) – up to 64 mm– Blocks more than 64 mm (solid)Blocks more than 64 mm (solid)– Bombs more than 64 mm (liquid)Bombs more than 64 mm (liquid)

TephraTephra

(Actual size of tephra)

Anatomy of a VolcanoAnatomy of a Volcano

Vent – in volcanic regions, an opening in Vent – in volcanic regions, an opening in the Earth’s surface through which lava, the Earth’s surface through which lava, ash and steam flowash and steam flow

Crater – opening at the top of a volcanoCrater – opening at the top of a volcano Dike – igneous rock that forms when Dike – igneous rock that forms when

magma is squeezed into a vertical crack magma is squeezed into a vertical crack and solidifies (crosses layers)and solidifies (crosses layers)

Sill – small body of igneous rock that Sill – small body of igneous rock that forms when magma is squeezed into a forms when magma is squeezed into a horizontal crack and then solidifies horizontal crack and then solidifies (parallel to layers)(parallel to layers)

Anatomy of a VolcanoAnatomy of a Volcano

Anatomy of a VolcanoAnatomy of a Volcano

Anatomy of a VolcanoAnatomy of a Volcano

Crater at the top of the ventCrater at the top of the vent

Evidence of VolcanoEvidence of Volcano

Volcanic neck: the core of a Volcanic neck: the core of a volcano’s vent that remains after the volcano’s vent that remains after the outer layers of lava and tephra have outer layers of lava and tephra have been eroded away from an extinct been eroded away from an extinct volcanovolcano

Caldera: the large opening formed at Caldera: the large opening formed at the top of a volcano when the crater the top of a volcano when the crater collapses into the vent following an collapses into the vent following an eruptioneruption

Volcanic NeckVolcanic Neck

Crater LakeCrater Lake

Crater LakeCrater Lake

The EndThe End

Each group member is responsible for knowing all 3 volcanoes AND additional features so make sure the information is recorded in your OWN notebook

Types of Volcanoes - Group Composite volcanoShield volcanoCinder Cone VolcanoCaldera and other interesting features of volcanoes

Each type of volcano the following information will be recorded in your notebook and reported to the group.

For your type of volcano, you will find:The structure / make up of the volcanoType of magma / lava produced; type of tephra produced How does this type of magma/lava relate to eruption the volcano producesExamples of this kind of volcano and the places they are located.Last eruption or most famous eruption and explain what happened.

Extra CreditExtra CreditFind a news article regarding Volcanoes Find a news article regarding Volcanoes

in a newspaper or magazine or onlinein a newspaper or magazine or onlineIf online: print, read If online: print, read andand highlighthighlight

TypeType two paragraphs: one paragraph two paragraphs: one paragraph summary and a one paragraph summary and a one paragraph

responseresponse

Give it to me Give it to me discreetlydiscreetly at the at the beginning of class BEFORE the beginning of class BEFORE the endend of of

the unit on volcanoes.the unit on volcanoes.