1 Intro to Volcanoes

2 What is a Volcano Volcano: a weak spot in the crust where molten rock (magma) comes to the surface Most volcanoes are located around subduction zones and hot spots Over 75% of worlds volcanoes are found th Pacific Rim (ring of fire)

3 How they form Volcanic eruptions occur when magma rises to the surfaceCaused as the asthenosphere melts A decrease in pressure (mid-ocean ridge or rift valley) An increase in temperature (hot spot) An increase in the amount of water in the asthenosphere (subduction zones)

4 Where Most volcanoes occur at Divergent boundariesConvergent bounders that have subduction Hot spots

5 Divergent Boundaries A decrease in pressure allows magma to rise as plates pull apart from one another These can often cause fissure volcanoes such as the Mid-Atlantic Ridge and the Great Rift Valley

6 Convergent BoundariesSubduction increase the amount of water in the asthenosphere which lowers the melting temp As the denser oceanic crust is pushed lower, it melts into magma Volcanoes can form on land or under water to rise up and form islands

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8 Hot spots Volcanoes can also occur at places that are not plate boundaries These hot spots are areas where hot magma rises from deep in Earth’s mantle Magma escapes where the crust is the thinnest or weakest It starts out solid then it melts when it reaches areas of lower pressure

9 Example of Hot Spot Volcanoes that make up Hawaii.

10 Volcano Anatomy

11 Four types Composite volcano (stratovolcano) Shield volcanoCinder Cone Fissure Volcanoes

12 Composite Volcano Also called a stratovolcanoMade of alternating layers of ash and lava Steep slopes, tall Explosive! Violent eruptions of thick lava and/ or ash and rock Most commonly form from subduction zone Examples: Mt. Shasta, Mt St. Helens, Pinatubo, Mt. Vesuvius

13 Mt. St. Helens, WA

14 Shield Volcano Large, broad volcanoes Gentle slopesMade from frequent lava eruptions Lave tends to be thin, runny Most often form at a hot spot Examples: Kilauea, and Mauna Loa in Hawaii

15 Mauna Loa, Hawaii

16 Cinder Cone Simplest type of volcanoMade of particles and chunks of lava, material ejected from vent Small with bowl-shaped top Often near other larger volcanoes Example: cinder cones around Shasta, Cerro Negro in Nicaragua

17 Krakatau, Indonesia

18 Cinder Cones Iceland

19 Fissure Volcanoes Form in long cracks where plates are pulled apart and near other volcanoes where the crust is weakened Typically near cinder cone or shield volcanoes

20 Fissure volcanoes

21 Yellowstone Check out how large some of the lava flows were from the Yellowstone Volcano!!!

22 How does a Caldera Form? A) A Volcano’s pressure starts to build upB) The Volcano releases large amounts of Lava C) As the Lava is released, the pressure decreases and the volcanic mountain begins to collapse, forming a concave shape in the center of the volcano. D) The center of the volcanic mountain may begin to fill with water and form a lake.

23 Crater Lake in Oregon State should actually be called Caldera Lake

24 So if that’s not cool Volcanoes are also beginning to play a role in extreme sports activities Volcano boarding is a real thing that you can go do That’s right you can go on vacation and basically snow board/sled down ash Just don’t fall

25 Label the parts of a volcanoWord Bank: Main Vent/Crater Secondary Vent Magma Chamber Lava Ash & Dust Cloud Tephra Bombs Cone