A Volcanoes PowerPoint Presentation

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Volcanoes and Plate Tectonics (part 2) “an opening in the Earth’s crust through which an eruption takes place”

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Volcanoes Three types Cinder Cones

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Cinder Cone

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Inside a Cinder Cone

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Cinder Cone Steep sloped sides (angles close to 40°) Relative to other volcanoes – small few hundreds of meters high Small explosive eruptions Made up of pyroclastic material (ash and tephra)

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Shield

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Montserrat Volcano eruption

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Shield Volcanoes The volcano have a very broad base, with gently sloping side (like a ‘shield’) Quiet eruptions Made up of layers of hot, mafic (basaltic) lava Hawaii is a good example of a shield volcano

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Composite

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Mount Saint Helens May 15, 1980

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Mount Saint Helens May 18 1980

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Mount Saint Helens May 18, 1980 Eruption

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Mount Saint Helens May 18 1980

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Mt. St. Helens devastation

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Mount Saint Helens September 10, 1980

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Mount Saint Helens September 24, 1984

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Mount Saint Helens (from Spirit Lake) May 15, 1980

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

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Popocatepetl composite volcano in Mexico is on the Ring of Fire

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Composite Volcanoes Steep sloped sides Very tall, 1000s of meters Very explosive eruptions, sometimes quiet eruptions (alternating for the most part) Made up of alternating layers of lava flows and silica rich (granitic) pyroclastic material. Mt. St. Helens is a good example of a composite volcano

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Volcanoes (cont.) Kinds of Eruptions: Quiet Shield Volcanoes – broad base, low angle slope Pillow lava – lava that occurs in mid-ocean ridges Basalt Plateaus – lava spreading evenly over a large area

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Volcanoes (cont.) Kinds of Eruptions: Rift Eruptions – Opening in the crust “spreading centers”: sea floor spreading (ocean) rift valley (continent) Lava ‘oozes’ out because of its mafic or basaltic composition

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Areas of Volcanic Activity (kinds of eruptions) Same regions as Earthquakes, which often serve as warning signs that a volcanic eruption might occur. Ring of Fire – around the rim of Pacific Ocean, subduction zone Ocean Ridge system Hotspots

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Volcanoes (cont.) Kinds of Eruptions: Ring of Fire – Subduction boundary Eruptions – Cinder cones and Composite Volcanoes Explosive eruptions, usually young mountain chains – like around the Ring of Fire

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Hot Spots Hot Spots – a place in the mantle where great amounts of heat are rising through the lithosphere. Causes of Hot Spots are still unknown – the source of the heat or ‘spot’ remains in the same location while the plate moves over it. For example: Hawaii

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Hot Spots

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Hot Spots

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Thermal signature of the Hawaiian Islands

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Plutonic – Igneous Rocks When masses of magma cools beneath the surface, it forms the cores of mountains. These ‘igneous intrusions’ are called Plutons. Plutons have different names depending on their size and shape

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Plutonic – Igneous Rocks Small intrusive igneous formations are: Dikes Sills Volcanic Necks Laccoliths…

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Plutonic – Igneous Rocks Laccolith – magma that buldges upward and formed dome mountains. (Henry Mountains, Utah and Black Hills, South Dakota) Batholith – a LARGE body (> 100 km3) of intrusive igneous rock. Forms the core of most mojor mountain ranges (Sierra Nevada) Stock – small batholith, less than100 km3

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Volcanoes

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Ruby Mountains Batholith

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La Paz Batholith

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East side of Sierra Batholith

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Granite Dome - Texas

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The End

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Volcano Essential Questions What are the 3 types of volcanoes?  How do they differ in eruptive force, composition of magma, ejected material and cone structure? Identify 3 tectonic settings where volcanoes form; which type of volcano forms at these locations? Explain how the composition of magma affects volcanic eruptions. What are the 5 types of pyroclastic material? List 3 events that MAY signal a volcanic eruption. What are the different igneous intrusions associated with volcanoes?

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For a Jolly Rancher of your choice… Send me an eMail with “Earth Science rocks my socks” in the title before the end of the volcano unit Only the first few will get this…. So don’t tell!!!!!!!!