Chapter 7 Volcano Volcano- vent in the Earth’s surface that often forms a mountain when layers of lava & volcanic ash erupt & build up

What causes a Volcano Heat & pressure cause rock to melt deep within the Earth magma is formed magma is less dense than rock around it & rises

Parts of a VolcanoB. Vent – opening in Earth’s surface that molten rock comes out of C. Crater – steep walled depression around a volcano’s vent e/earth/volcanoes/index.wemlhttp:// e/earth/volcanoes/index.weml

D. Hot Spots areas where magma from deep in Earth’s mantle has melted through the crust to form several volcanoes

Ex. The Hawaiian Island chain the Pacific Plate is moving over a stationary hot spot Kauai is the oldest Lo’ihi an underwater volcano will form the next island in the chain

II. Where does the word Volcano come from? The word Volcano comes from the ancient Roman god Vulcan Vulcan was thought to be living inside the island mountain of Vulcano, off the coast of Italy Blacksmith to the Gods, he forged thunderbolts on his anvil & hammered out the armor of Hercules

III. Magma & Lava A. Felsic – high in silica (see chart) B. Mafic - low in silica (see chart) · Viscosity – a fluids resistance to flow

C. Gases in Magma Magma containing large amounts of dissolved gases tends to produce more explosive eruptions Top 3 gases released by a volcano Water Vapor Carbon Dioxide Sulfur gases

D. Tephra –volcanic material of various sizes, from ash to large rocks called bombs blocks ash & lapilli reticulite Pele’s hair

IV. Volcanoes & Eruptions A. Cinder Cones short, steep slopes, like an upside down ice cream cone explosive eruptions of pumice, ash, & tephra

Ex. #1 Krakatau Indonesia 1883 the loudest volcanic explosion in the world formed a tsunami that killed 36,000 people Indian Plate subducting under the Eurasian Plate

Krakatau Indonesia docs/volc_images/southeast_asi a/indonesia/krakpics.htmlhttp://volcano.und.nodak.edu/vw docs/volc_images/southeast_asi a/indonesia/krakpics.html

Ex. #2 Paricutin Formed in 1943 Dominic Pulido, a Tarascan Indian farmer in central Mexico, witnessed the start of the eruption of a volcano Formed in a cornfield that was ready to be planted first volcano birth man has witnessed

B. Shield Volcanoes quiet eruptions of basaltic lava wide and somewhat flat like an overturned Viking shield formed by successive flows of runny lava, usually over a long period of time

Ex. Of Shield Volcanoes Mauna Loa & Kilauea in Hawaii; hot spots earth/volcanoes/htmlhttp:// earth/volcanoes/html

C. Stratovolcanoes/Compo site Cones Look like “regular” non- volcanic mountains from a distance Eruption can vary between quiet & violent Eruptions of ash & gases leave a tephra layer

Composite Cones Continued Eruptions of lava can alternate with tephra during less explosive times Found mostly where Earth’s plates converge (subduction zones) earth/animations/volcanoes/inde x.html earth/animations/volcanoes/inde x.html

Ex. 1 Mt. Pinatubo Located in the Philippines Pacific Plate subducting under the Philippine plate biggest eruption of ½ of the century erupted in 1991

Mt. St. Helens Located in Washington State Erupted May 18th 1980 Juan de Fuca plate subducting under the N. American plate Very little lava but large amounts of dust & gas

Ex. # 3 Mt. Vesuvius Located in Italy African plate subducting under the Eurasian plate Violent eruption of AD 79 Thick lava full of gases caused the violent eruption of ash that covered Pompeii