Causes of Volcanoes pg. 121

Things to know when talking about Volcanoes… Volcanoes release material from the mantle. Volcanoes release material from the mantle.

Magma- inside the Earth Lava- on the surface Both are made up of the same mantle material!

The mantle is basically solid, so how do we get liquid- really liquid- magma / lava? Three ways to melt the solid mantle… Add water Add water Relieve (decrease or lower) pressure. Relieve (decrease or lower) pressure. Increase the temperature Increase the temperature

What are causes of volcanic eruptions? What are causes of volcanic eruptions? 1. Magma rises in the mantle. 2. Releases gas. 3. Gas expands and increases pressure under surface until finally it erupts.

Where do volcanoes form? 80% of volcanoes form at convergent boundaries when oceanic lithosphere is subducted.

What is the “Ring of Fire?” “ring” of volcanoes “ring” of volcanoes plate boundaries of the Pacific Plate- oceanic plate subducts under the converging continents. plate boundaries of the Pacific Plate- oceanic plate subducts under the converging continents.

Why does subduction produce magma? 1. Oceanic crust contains water, when the crust melts, the water is released, forming magma 2. The magma then rises to form a volcano. Trench

Where else do volcanoes form? 15% of volcanoes form at divergent plate boundaries. (like mid- ocean ridges)

How does magma form at a divergent boundary? 1.deep cracks called a rift zone form between the plates 2. Lowers pressure on mantle at boundary. 3. Magma forms and rises. Less pressure at the boundary

What about volcanoes that form far from either type of boundary?

What are Hotspots? Volcanoes that form far away from a plate boundary Hawaii was formed from a hotspot

Hotspots stay in the same location as the plate moves across it…

Yellowstone National Park- Old Faithful Geyser Geyser

The northeastern part of Yellowstone Caldera, with the Yellowstone River flowing through Hayden Valley and the caldera rim in the distance

Where are the world’s hot spots?

Extinct volcanoes—have not erupted in recorded history Dormant — not currently active Active volcanoes— currently showing volcanic activity Volcanoes are classified into 3 categories

Can we predict a volcano eruption? Small quakes Small quakes Volcanic gases Volcanic gases Bulging mountains Bulging mountains Changes in surface temperature Changes in surface temperature Scientists look for:

Types of eruptions

Quiz pg. 2- -#’s 2,3,4 and 9 are extra credit (1 pt. each) Quiz pg. 3 (20 points) 1 picture, 1 explanation. Quiz pg. 3 (20 points) 1 picture, 1 explanation. 1. Draw a convergent boundary. 1. Draw a convergent boundary. 2. Show subduction of one plate. (Hint: look at #11 in your notebook) 2. Show subduction of one plate. (Hint: look at #11 in your notebook) 3. Show where a volcano would form. 3. Show where a volcano would form. 4. Label at least four things. 4. Label at least four things. 5. Write an explanation of why converging plates might result in the formation of a volcano. 5. Write an explanation of why converging plates might result in the formation of a volcano.

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