Volcanoes and Plate Tectonics (part 2)

VolcanoesVolcanoesand Plate Tectonicsand Plate Tectonics (part 2) (part 2)

““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 Three typesThree types

Cinder Cones Cinder Cones

Cinder ConeCinder Cone

Inside a Cinder ConeInside a Cinder Cone

Cinder ConeCinder Cone Steep sloped sides (angles close to Steep sloped sides (angles close to

4040°)°) Relative to other volcanoes – small Relative to other volcanoes – small

few hundreds of meters highfew hundreds of meters high Small explosive eruptionsSmall explosive eruptions Made up of pyroclastic material (ash Made up of pyroclastic material (ash

and tephra)and tephra)

ShieldShield

Montserrat Volcano eruption Montserrat Volcano eruption

Shield VolcanoesShield Volcanoes The volcano have a very broad base, The volcano have a very broad base,

with gently sloping side (like a with gently sloping side (like a ‘shield’)‘shield’)

Quiet eruptionsQuiet eruptions Made up of layers of hot, mafic Made up of layers of hot, mafic

(basaltic) lava(basaltic) lava Hawaii is a good example of a shield Hawaii is a good example of a shield

volcanovolcano

CompositeComposite

Mount Saint HelensMount Saint HelensMay 15, 1980May 15, 1980

Mount Saint HelensMount Saint HelensMay 18 1980May 18 1980

Mount Mount Saint Saint HelensHelensMay 18, May 18, 19801980

EruptionEruption

Mount Saint HelensMount Saint HelensMay 18 1980May 18 1980

Mt. St. Helens devastationMt. St. Helens devastation

Mount Saint HelensMount Saint Helens September 10, 1980 September 10, 1980

Mount Saint HelensMount Saint HelensSeptember 24, 1984September 24, 1984

Mount Saint Helens Mount Saint Helens (from Spirit Lake) May 15, (from Spirit Lake) May 15,

19801980

Mount Saint Helens Mount Saint Helens (from Spirit Lake) May 19,1982(from Spirit Lake) May 19,1982

Popocatepetl composite volcano in Mexico is Popocatepetl composite volcano in Mexico is on the Ring of Fire on the Ring of Fire

Composite VolcanoesComposite Volcanoes Steep sloped sidesSteep sloped sides Very tall, 1000s of metersVery tall, 1000s of meters Very explosive eruptions, sometimes Very explosive eruptions, sometimes

quiet eruptions (alternating for the most quiet eruptions (alternating for the most part)part)

Made up of alternating layers of lava Made up of alternating layers of lava flows and silica rich (granitic) pyroclastic flows and silica rich (granitic) pyroclastic material.material.

Mt. St. Helens is a good example of a Mt. St. Helens is a good example of a composite volcanocomposite volcano

VolcanoesVolcanoes (cont.) (cont.) Kinds of Eruptions:Kinds of Eruptions:

Quiet Quiet Shield VolcanoesShield Volcanoes – –

broad base, low broad base, low angle slopeangle slope

• Pillow lavaPillow lava – lava that – lava that occurs in mid-ocean occurs in mid-ocean ridgesridges

• Basalt PlateausBasalt Plateaus – lava – lava spreading evenly spreading evenly over a large areaover a large area

VolcanoesVolcanoes (cont.) (cont.) Kinds of Eruptions:Kinds of Eruptions:

• Rift Eruptions – Opening in the Rift Eruptions – Opening in the crust crust

““spreading centers”: spreading centers”: • sea floor spreading (ocean)sea floor spreading (ocean)• rift valley (continent)rift valley (continent)

Lava ‘oozes’ out because of its Lava ‘oozes’ out because of its mafic or basaltic compositionmafic or basaltic composition

Areas of Volcanic ActivityAreas of Volcanic Activity(kinds of eruptions)(kinds of eruptions)

Same regions as Earthquakes, which Same regions as Earthquakes, which often serve as warning signs that a often serve as warning signs that a volcanic eruption might occur.volcanic eruption might occur.

1.1. Ring of Fire – around the rim of Ring of Fire – around the rim of Pacific Ocean, subduction zonePacific Ocean, subduction zone

2.2. Ocean Ridge systemOcean Ridge system3.3. HotspotsHotspots

VolcanoesVolcanoes (cont.) (cont.) Kinds of Eruptions:Kinds of Eruptions:

Ring of Fire –Ring of Fire –Subduction boundary EruptionsSubduction boundary Eruptions – – Cinder cones and Composite VolcanoesCinder cones and Composite Volcanoes

ExplosiveExplosive eruptions, usually young eruptions, usually young mountain chains – like around the mountain chains – like around the Ring of FireRing of Fire

Hot SpotsHot SpotsHot SpotsHot Spots – a place in the mantle – a place in the mantle

where great amounts of heat are where great amounts of heat are rising through the lithosphere.rising through the lithosphere.

Causes of Hot Spots are still Causes of Hot Spots are still unknown – the source of the heat or unknown – the source of the heat or ‘spot’ remains in the same location ‘spot’ remains in the same location while the plate moves over it. while the plate moves over it.

For example: HawaiiFor example: Hawaii

Hot SpotsHot Spots

Chain of the Hawaiian Chain of the Hawaiian IslandsIslands

Seamount – large Seamount – large submarine volcanic submarine volcanic mountainmountain rising at  rising at least 1,000 m (3,300 least 1,000 m (3,300 feet) deep-sea floor; feet) deep-sea floor;

Most of the volcanoes of Most of the volcanoes of the Hawaiian-Emperor the Hawaiian-Emperor Chain are completely Chain are completely underwater, and known as underwater, and known as seamountsseamounts

Plutonic – Igneous RocksPlutonic – Igneous RocksWhen masses of magma cools beneath When masses of magma cools beneath

the surface, it forms the cores of the surface, it forms the cores of mountains. mountains.

These ‘igneous intrusions’ are called These ‘igneous intrusions’ are called PlutonsPlutons..

Plutons have different names depending Plutons have different names depending on their size and shapeon their size and shape

Plutonic – Igneous RocksPlutonic – Igneous RocksSmall intrusive igneous formations are:Small intrusive igneous formations are: Dikes –sheets of igneous rock (usually basalt or Dikes –sheets of igneous rock (usually basalt or

diabase) that cut across the rock layersdiabase) that cut across the rock layers

Sills – sheets that cut parallel to the rock layers Sills – sheets that cut parallel to the rock layers (Palasades, along Hudson River)(Palasades, along Hudson River)

Volcanic Neck – Plug of a hardened/solidified lava Volcanic Neck – Plug of a hardened/solidified lava left in a volcanic vent; when an extinct volcano is left in a volcanic vent; when an extinct volcano is eroded – only the volcanic neck is left (Monument eroded – only the volcanic neck is left (Monument Valley, AZ)Valley, AZ)

Plutonic – Igneous RocksPlutonic – Igneous Rocks Laccolith – magma that buldges Laccolith – magma that buldges

upward and formed dome mountains. upward and formed dome mountains. (Henry Mountains, Utah and Black (Henry Mountains, Utah and Black Hills, South Dakota) Hills, South Dakota)

Batholith – a LARGE body (> 100 kmBatholith – a LARGE body (> 100 km33)) of intrusive igneous rock. Forms the of intrusive igneous rock. Forms the core of most mojor mountain ranges core of most mojor mountain ranges (Sierra Nevada) (Sierra Nevada)

Stock – small batholith, less than100 Stock – small batholith, less than100 kmkm33

VolcanoesVolcanoes

Ruby Mountains BatholithRuby Mountains Batholith

La Paz BatholithLa Paz Batholith

East side of Sierra BatholithEast side of Sierra Batholith

Granite Dome - TexasGranite Dome - Texas

The EndThe End

Volcano Essential Questions

1. What are the 3 types of volcanoes?  How do they differ in eruptive force, composition of magma, ejected material and cone structure?

2. Identify 3 tectonic settings where volcanoes form; which type of volcano forms at these locations?

3. Explain how the composition of magma affects volcanic eruptions.

4. What are the 5 types of pyroclastic material?5. List 3 events that MAY signal a volcanic

eruption.6. What are the different igneous intrusions

associated with volcanoes?

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