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Ch. 18 – Volcanic Activity   Magma is a mixture of molten rock, suspended mineral grains, and dissolved gases deep beneath Earth’s surface. – –Video-Earth’s.

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Presentation on theme: "Ch. 18 – Volcanic Activity   Magma is a mixture of molten rock, suspended mineral grains, and dissolved gases deep beneath Earth’s surface. – –Video-Earth’s."— Presentation transcript:

1 Ch. 18 – Volcanic Activity   Magma is a mixture of molten rock, suspended mineral grains, and dissolved gases deep beneath Earth’s surface. – –Video-Earth’s InteriorVideo-Earth’s Interior – –These rocks start to melt a temperatures between 800°C and 1200°C. – –This occurs and the base of the lithosphere and the asthenosphere.   The pressure and amount of water in the rocks pores also affect the temperature a which magma forms.   Volcanoes-Intro. Volcanoes-Intro.   Volcanoes-Mountains. Volcanoes-Mountains.

2 Types of Magma  1. Basaltic Magma – made mostly of basalt. –Mostly found in the Hawaiian Islands  2. Andesitic Magma – made mostly of andesite. –Mt. St. Helens and Tamobra in Indonesia  3. Rhyolitic Magma – made mostly of granite. –Dormant volcanoes in Yellowstone National Park.  Active Volcanoes  Pg. 473 (fig. 18-2)

3 Magma Composition  TABLE 18-1 (Pg. 474)  Viscosity – the resistance to flow –The hotter the magma or lave the lower the viscosity. Why? –It moves and flows easier when it’s hot. –Video-lava Video-lava  Rhyolitic magma has the highest viscosity and highest explosiveness. –Found in continental crust  Basaltic magma has the lowest viscosity and lowest explosiveness. –Found in both oceanic and continental crust.

4 Intrusive Activity  Magma is less dense than the rock that surrounds it, so it will eventually rise the Earth’s surface.  As the magma cools forms under the Earth’s surface plutons can form. These are igneous rock bodies.  Plutons are classified by their size, shape, and relationship to surrounding rocks.  The largest plutons are called batholiths. They cover over 100 km2 and take millions of years to form. –Most batholiths in N. America are composed mostly of granite. –Pg. 477 – Fig. 18-5

5  Stocks are smaller in size and irregular shaped plutons.  Laccoliths are smaller yet and have mushroom-shaped plutons with a round top and flat bottom.  Sills are plutons that form when magma intrudes parallel to layers of rock.  Dikes are plutons that cut across preexisting rocks.  Most plutons form from mountain building processes. –When the continental crust is forced down into the lower mantle it melts and eventually cools as batholiths.

6 Volcanoes  What are some characteristics of a volcano?  A vent is the area in a volcano were lava can flow to the surface of a volcano.  The crater is the bowl-shaped depression near the top of the volcano.  Large craters are called calderas. –Depression that forms when the top or side of a volcano collapses into the magma chamber. –Ex. Crater Lake (pg. 481)  Landscape features (exterior) include: vents, craters, and calderas.

7 Types of Volcanoes  Shield Volcanoes are mountains with broad gentle slopping sides and a nearly circular base. –Forms from several layers of basaltic lava –They have low viscosity and low explosions.  Cinder-Cone Volcanoes form when material is ejected high into the air and falls back to the Earth and piles up around the vent. –Steep slopes & more explosiveness than shield volcanoes. –Forms as tephra ejected high into the air fall back to the Earth and pile around the vent. –Video-volcano types Video-volcano typesVideo-volcano types

8  Composite Volcanoes form when layers of volcanic fragments alternate with lava. –Larger than cinder-cone volcanoes. –Violently explosive in nature. –Mt. St. Helens and Mt. Rainer  Video-St. Helens Video-St. Helens Video-St. Helens  elated elated elated –Made from layers of tephra and lava. –Largest of the volcanoes.  Tephra are rock fragments that are thrown into the air during the eruption. –Dust is the smallest fragments –Ash are the larger fragments, but still less than 2 mm in size.  Pyroclastic flow is rapidly moving volcanic material and may contain hot, poisonous gases.

9  Volcanoes can occur in convergent boundaries (come together) and divergent boundaries (spread apart). –Fig (pg. 485) –Mainly convergent boundaries. –Video-Ring of Fire Video-Ring of FireVideo-Ring of Fire  Hot spots are regions away from plate boundaries were volcanoes form. –Hawaiian Islands have several hot spot volcanoes. –Video-Hot Spots Video-Hot SpotsVideo-Hot Spots  Volcanism that occurs under water along mid- ocean ridges are rift volcanism  Volcanoes are proof that the Earth is dynamic planet.  Video-Deadly Volcanoes Video-Deadly Volcanoes Video-Deadly Volcanoes


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