Volcanoes and Magma

1. Volcanoes and Magma Julie, Liz and Tyler

2. Volcanic eruptions occur only in certain places… they do not occur randomly ONE WAY THEY OCCUR…

3. Plates colliding… • The Earth's outermost shell the lithosphere is broken into a series of slabs known as lithospheric or tectonic plates. • These plates are rigid, and they float on the hotter, softer layer in the Earth's mantle. As the plates move about, they spread apart, collide, or slide past each other. = A Volcano occurs most frequently at plate boundaries… when plates collide together!

4. Land and underwater volcanoes… Mount St. Helens is typical of more than 80 % of the volcanoes that have formed on land. Submarine or underwater volcanoes usually originate rear the Mid-Oceanic Ridge system *Known as subduction zone volcanoes, they occur along the edges of continents where one plate dives, or subducts, beneath a second plate. *Western Washington and Oregon are near a subduction zone and in a region likely to experience future volcanic activity. Kansas and Nebraska are not.

5. Another way volcanoes occur…

6. Hot spots… • Some volcanoes occur in the interior of plates at areas called hot spots, are caused by upwelling of deep mantle plumes. -Hawaii is the best known example of hot spot volcanism! **Other examples of hot spot volcanoes are located in …Iceland Piton de la Fournaise Canary Islands Heard Island McDonald Island

7. Intrusive Igneous Rocks (Plutonic Rocks): Plutonic rocks (also called intrusive igneous rocks ) are those that have solidified below ground. When magmas crystallize deep underground they look different from volcanic rocks because they cool more slowly and, therefore, have larger crystals. Igneous rocks cooled beneath the Earth's surface are called intrusive rocks.

8. Intrusive Igneous Rocks: Intrusive, or plutonic igneous rock forms when magma is trapped deep inside the Earth. Great globs of molten rock rise toward the surface. Some of the magma may feed volcanoes on the Earth's surface, but most remains trapped below, where it cools very slowly over many thousands or millions of years until it solidifies. Slow cooling means the individual mineral grains have a very long time to grow, so they grow to a relatively large size. Intrusive rocks have a coarse grained texture.

9. The three things that create magma… • increase in temperature in the asthenosphere • decrease in pressure ~ pressure-release melting- melting is caused by decrease in pressure • additional water, a wet rock melts at a lower temperature than an identical rock that is not wet.

10. Intrusive Igneous Rock… • Pluton – in the Earth’s crust granitic magma solidifies and granite is formed in a large mass. • Granitic magma is formed near the base of the crust and is surrounded by hot plastic rock. Magma then rises. The plastic rock fills back in behind it. • batholith – is exposed on the earth’s surface for more than 100 square kilometers. Is made up of many smaller plutons that rise sequentially over time • stock – less than 100 kilometers is exposed on the earth’s surface • dike – sheet like, forms when magma slides into a fracture • still – sheet like rock parallel to layering, forms the same way as dikes do

11. Group 3 ROCKS…get it???