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Holy Smokes!. A Volcano Primer. What we will learn. Plates move and cause major events. The effects of volcanic eruptions on earth. Location of volcanic regions and why they are found at those places. 4. What hot spots are and where they are formed. What is a volcano?.

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holy smokes

Holy Smokes!

A Volcano Primer

what we will learn
What we will learn
  • Plates move and cause major events.
  • The effects of volcanic eruptions on earth.
  • Location of volcanic regions and why they are found at those places.

4. What hot spots are and where they are formed.

what is a volcano
What is a volcano?
  • A volcano is a weak spot in the crust where magma comes out.
  • Magma is molten mixture of rock-forming substances, gases, and water from the mantle.
  • When magma reaches earth’s surface, it is called lava.
  • When lava cools, it forms rock.
volcanoes and plate boundaries
Volcanoes and plate boundaries
  • Ring of Fire- A major volcanic belt that is formed by many volcanoes that rim the Pacific Ocean.
  • Volcanic belts form along the boundaries of Earth’s plates.
          • Most volcanoes form along diverging plate boundaries such as mid-ocean ridges and along converging plate boundaries where subduction takes place.
          • Ex: Mount Etna formed near Eurasian and African plate boundaries.
diverging boundaries
Diverging Boundaries
  • Volcanoes form along mid-ocean ridges where plates diverge.
  • Ridges are long underwater mtn. ranges that have a rift valley down the center.
  • Lava pours out of cracks in ocean floor, building new mtns.

Volcanoes also form along diverging plate boundaries on land.

Ex: There are several large volcanoes along the Great Rift Valley in East Africa.

converging boundaries
Converging Boundaries
  • Many volcanoes form near converging plate boundaries where oceanic plates return to the mantle.
  • Volcanoes may form where 2 oceanic plates collide or where an oceanic plate collides with a continental plate.
          • Where 2 oceanic plates collide, subduction takes place and the older, denser plate sinks beneath a deep ocean trench into the mantle.
converging boundaries cont
Converging boundaries (cont)
  • Some of the rock above the subducting plate melts and forms magma.
  • The magma is less dense than the rock around it, so it rises toward the surface, & eventually breaks through the ocean floor, and creates a volcano.
quick check do not look at your notes or book
Quick Check- Do NOT look at your notes or book.

1. What’s the difference in magma and lava?

2. Why does magma rise when it is inside earth?

3. What is the ring of fire?

4. Why do volcanoes form at divergent plate boundaries?

island arc
Island Arc
  • An island arc is a string of volcanic islands.
  • The curve of an island arc is the same curve as the trench beneath it. Ex; Japan, New Zealand, Indonesia, Philippines, Aleutians, and Caribbean islands.

Volcanoes also occur where an oceanic plate is subducted beneath a continental plate.

  • This type of collision produced volcanoes of the Andes Mtns in South America and the volcanoes of the Pacific NW in the USA.
hot spots
Hot Spots
  • A Hot Spot is an area where material from deep within the mantle rises and then melts, forming magma.
  • A volcano forms above a hot spot when magma erupts through the crust and reaches the surface.
          • Some hot spots lie in the middle of plates far from any plate boundaries.
          • A hot spot in the ocean floor can gradually form a series of volcaicmtns.
examples of hot spots
Examples of hot spots
  • Hawaiian islands formed one by one over millions of years as the Pacific plate drifted over a hot spot.
  • Hot spots can also form under the continents. Ex: Yellowstone National Park in Wyoming marks a hot spot under the North American plate.

Write a ½ page summary answering these questions.

  • What is a volcano?
  • Where are volcanoes formed?
  • How did the volcanoes in the Andes Mtns form?

4. What is a hot spot and how does it form?

5. Why are volcanoes are located in the ring of fire?

3 basic volcano shapes
3 Basic Volcano shapes
  • Shape
    • tells us something about how the volcano was formed.
  • Cinder Cone
  • Shield
  • Composite Cone
1 cinder cone volcano
1. Cinder Cone Volcano
  • Formed by Tephra (volcanic cinders, bit of solidified lava, and bits of rocks) thrown into the air during an eruption & then fall back down around the vent (volcanic opening) forming a steep-sided loosely packed volcano.
example cinder cone volcano
ExampleCinder Cone Volcano
  • Parícutin Volcano in Mexico is a great example of a cinder cone volcano.
parac tin
  • On February 20, 1943, a Mexican farmer noticed that a hole in his cornfield that had been there for as long as he could remember was giving off smoke.
  • Throughout the night, hot glowing cinders were thrown high into the air.
  • In just a few days, a cinder cone several hundred meters high covered his cornfield.
2 shield volcano
2. Shield Volcano
  • Quiet eruptions of basaltic lava spread out in flat layers.
  • The buildup of these layers forms a broad volcano with gently sloping sides.
shield volcano
Shield Volcano
  • The shapes of these volcanoes reflect the fact that they are constructed of lava flows that erupted non-explosively.
  • It is usually many times larger than a composite cone or cinder cone volcano.

Mauna Kea volcano

picture from www.usgs.gov

example of shield volcano
Example of Shield Volcano
  • Mauna Loa
  • Mt. Kilauea
    • Probably one of the world’s most active volcanoes.
    • The eruption of Kilauea Volcano that began in 1983 continues at the cinder-and-spatter cone of Pu`u `O`o

Mt. Kilauea

Picture from http://www.britannica.com/eb/art-89176/Hawaiis-Kilauea-is-an-active-volcano

3 composite volcano
3. Composite Volcano
  • This type of volcano is composed of explosively erupted pyroclastic materials layered with lava flows and volcanic debris.
    • An explosive period can release gas and ash, forming a tephra layer.
    • Then, the eruption can switch to a quieter period, erupting lava over the top of the tephra layer.
example of composite volcano
Example of Composite Volcano
  • Mount St. Helen’s
    • Erupted in 1980
    • 57 fatalities
    • Over 7000 big game animals perished
    • 4 billion board feet of timber (enough to build about 300,000 two-bedroom homes) destroyed
    • Destroyed 27 bridges, nearly 200 homes. Blast and lahars destroyed more than 185 miles of highways and roads and 15 miles of railways.
example of composite volcano1
Example of Composite Volcano
  • Mount Pinatubo
    • Erupted in 1991
    • Killed 847 people
    • 184 people injured
    • 10, 000 home destroyed and another 5,000 were damaged.
    • The ash cloud took one year to spread around the globe, reducing global temperatures. This resulted in
      • Floods in 1993 along the Mississippi River
      • Drought in Africa in 1993
      • The US had its 3rd wettest & coldest winter on record.
example of composite volcano2
Example of Composite Volcano
  • Krakatau
    • One of the most violent eruptions in recent times occurred on an island in the Sunda Straits near Indonesia in August of 1883.
    • Krakatau, a volcano on the island, erupted with such force that the island disappeared.
example of composite volcano krakatau
Example of Composite Volcano Krakatau
  • Killed 36,000 people most were killed by a giant tsunami
  • Destroyed 160 villages
  • Fine ashes from the eruption were carried by upper level winds as far away as New York City
  • Volcanic dust lowered global temperatures for five years, this caused
example of composite volcano krakatau1
Example of Composite Volcano Krakatau
  • Unusual sunsets and weather patterns for three years
  • Evidence:
    • William Ashcroft’s paintings
    • The Scream
what determines how explosive an eruption is
What determines how explosive an eruption is?
  • Amount of trapped gases
  • Amount of Water Vapor
  • Composition of Magma
1 trapped gases
1. Trapped Gases
  • Gases such as water vapor and carbon dioxide are trapped in magma by the pressure of the surrounding magma and rock.
    • Gas escapes easily from some magma during quiet eruptions.
    • However, gas that builds up to high pressures eventually causes explosive eruptions.
2 amount of water vapor
2. Amount of Water Vapor
  • The magma at some convergent plate boundaries contains a lot of water vapor.
  • This is because oceanic plate material and some of its water slide under other plate material at some convergent plate boundaries.
  • The trapped water vapor in the magma can cause explosive eruptions.
3 magma composition
3. Magma Composition
  • The composition (what it is made of) determines how explosive a volcano will be.
magma composition basaltic
Magma CompositionBasaltic
  • Magma made of basalt is very fluid, allowing trapped gases to escape easily.
  • Volcanoes with basaltic lava have quiet, non-explosive eruptions.
magma composition basaltic1
Magma CompositionBasaltic
  • If the same lava flows at a lower temperature, a stiff, slowly moving aa (AH-ah) lava forms.

As pahoehoe (pa-HOY-hoy) lava cools, it forms a ropelike structure.

rock structures shaped like tubes, balloons, or pillows.

  • Volcanoes with basaltic lava produce:
  • underwater pillow lava formations
magma composition basaltic examples
Magma CompositionBasalticExamples
  • You can find volcanoes with basaltic lava
    • Hawaiian Volcanoes, including
      • Kilauea
      • Mona Loa
    • Iceland
      • Heimaey
      • Hekla
magma composition granitic lava
Magma CompositionGranitic Lava
  • Silica-rich, or granitic (also called rhyolite) magma produces explosive eruptions.
  • Silica-rich granitic magma is thick, and gas gets trapped inside, causing pressure to build up.
magma composition granitic lava1
Magma CompositionGranitic Lava
  • “If it had erupted in a populated area…"The magnitude of the eruption can perhaps be best realized if one could imagine a similar outburst centered in New York City. All of Greater New York would be buried under from ten to fifteen feet of ash; Philadelphia would be covered by a foot of gray ash and would be in total darkness for sixty hours; Washington and Buffalo would receive a quarter of an inch of ash, with a shorter period of darkness. The sound of the explosion would be heard in Atlanta and St. Louis, and the fumes noticed as far away as Denver, San Antonio, and Jamaica."
  • Some examples of granitic volcanoes are
    • Yellowstone Caldera
      • It is a super voclano!
    • Katmai, Alaska
      • Last eruted in 1912.
magma composition andesitic lava
Magma CompositionAndesitic Lava
  • Volcanoes with andesitic magmas have violent, explosive eruptions.
  • It often forms at convergent plate boundaries where one plate slides under the other.
magma composition andesitic lava1
Magma CompositionAndesitic Lava
  • The word andesitic comes from the Andes, which are mountains located along the western edge of South America, where andesite rock is common.
  • Many of the volcanoes encircling the Pacific Ocean also are made of andesite.
magma composition andesitic lava2
Magma CompositionAndesitic Lava

Mount Pelee, Martinique

    • Famous for the May 8, 1902 eruption which killed 29,000 people and destroyed the city of St. Pierre. This is the largest number of causalities for a volcanic eruption this century.
  • Mayon, Phillipines
    • It is the most active volcano in the Philippines. Since 1616, Mayon has erupted 47 times.
    • It’s 1814 eruption killed 1,600.
volcanoes in a nutshell
Volcanoes in a nutshell
  • Three volcano types
    • Shape
      • Cinder
        • Violent eruptions
      • Composite
        • Violent & quiet eruptions
      • Shield
        • Quiet Eruptions
volcanoes in a nutshell1
Volcanoes in a nutshell
  • Three factors affect how violent an eruption will be
    • Water Vapor
      • More water vapor = bigger explosion
    • Trapped Gasses
      • How easily the gas escapes determines how violent the explosion
      • Easy escape = quiet eruption
      • Difficult to escape = explosive eruption
    • Magma Type
      • Basaltic Magma = quiet explosion
      • Granitic/Andesitic = violent eruptions
resources used
Resources used
  • Volcano World
    • http://volcano.und.edu/
  • US Geologic Survey
    • http://www.usgs.gov/
  • Glencoe Earth Materials & Processes