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)
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)
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
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.