Intro to Volcanoes

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)

How they form Volcanic eruptions occur when magma rises to the surface Caused 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)

Where Most volcanoes occur at Divergent boundaries Convergent bounders that have subduction Hot spots

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

Convergent Boundaries Subduction 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

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

Example of Hot Spot Volcanoes that make up Hawaii.

Volcano Anatomy

Four types Composite volcano (stratovolcano) Shield volcano Cinder Cone Fissure Volcanoes

Composite Volcano Also called a stratovolcano Made 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

Mt. St. Helens, WA

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

Mauna Loa, Hawaii

Cinder Cone Simplest type of volcano Made 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

Krakatau, Indonesia

Cinder Cones Iceland

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

Fissure volcanoes

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

How does a Caldera Form? A) A Volcano’s pressure starts to build up B) 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.

Crater Lake in Oregon State should actually be called Caldera Lake

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

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