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

Volcanoes Three types  Cinder Cones

Cinder Cone

Inside a Cinder Cone

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

Shield

Montserrat Volcano eruption

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

Composite

Mount Saint Helens May 15, 1980

Mount Saint Helens May

Mount Saint Helens May 18, 1980 Eruption

Mount Saint Helens May

Mt. St. Helens devastation

Mount Saint Helens September 10, 1980

Mount Saint Helens September 24, 1984

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

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

Popocatepetl composite volcano in Mexico is on the Ring of Fire

Composite Volcanoes Steep sloped sides Steep sloped sides Very tall, 1000s of meters Very tall, 1000s of meters Very explosive eruptions, sometimes quiet eruptions (alternating for the most part) 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. 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 Mt. St. Helens is a good example of a composite volcano

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

Volcanoes (cont.) Kinds of Eruptions: Rift Eruptions – Opening in the crust Rift Eruptions – Opening in the 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 mafic or basaltic composition

Areas of Volcanic Activity (kinds of eruptions) Same regions as Earthquakes, which often serve as warning signs that a volcanic eruption might occur. 1. Ring of Fire – around the rim of Pacific Ocean, subduction zone 2. Ocean Ridge system 3. Hotspots

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

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. 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 For example: Hawaii

Hot Spots

Chain of the Hawaiian Islands Seamount – large submarine volcanic mountain rising at least 1,000 m (3,300 feet) deep-sea floor; Seamount – large submarine volcanic mountain rising at least 1,000 m (3,300 feet) deep-sea floor; Most of the volcanoes of the Hawaiian-Emperor Chain are completely underwater, and known as seamounts Most of the volcanoes of the Hawaiian-Emperor Chain are completely underwater, and known as seamounts

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

Plutonic – Igneous Rocks Small intrusive igneous formations are: Dikes –sheets of igneous rock (usually basalt or diabase) that cut across the rock layers Dikes –sheets of igneous rock (usually basalt or diabase) that cut across the rock layers Sills – sheets that cut parallel to the rock layers (Palasades, along Hudson River) Sills – sheets that cut parallel to the rock layers (Palasades, along Hudson River) Volcanic Neck – Plug of a hardened/solidified lava left in a volcanic vent; when an extinct volcano is eroded – only the volcanic neck is left (Monument Valley, AZ) Volcanic Neck – Plug of a hardened/solidified lava left in a volcanic vent; when an extinct volcano is eroded – only the volcanic neck is left (Monument Valley, AZ)

Plutonic – Igneous Rocks Laccolith – magma that buldges upward and formed dome mountains. (Henry Mountains, Utah and Black Hills, South Dakota) Laccolith – magma that buldges upward and formed dome mountains. (Henry Mountains, Utah and Black Hills, South Dakota) Batholith – a LARGE body (> 100 km 3 ) of intrusive igneous rock. Forms the core of most mojor mountain ranges (Sierra Nevada) Batholith – a LARGE body (> 100 km 3 ) of intrusive igneous rock. Forms the core of most mojor mountain ranges (Sierra Nevada) Stock – small batholith, less than100 km 3 Stock – small batholith, less than100 km 3

Volcanoes

Ruby Mountains Batholith

La Paz Batholith

East side of Sierra Batholith

Granite Dome - Texas

The End

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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