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Volcanoes Liquid Hot Magma. Tungerahua Volcano, Ecuador Picture by Alcinoe Calahorrano Volcano Stats • Definition of Volcano – Mountain that forms when molten rock (magma) is forced to the Earth’s surface • Number of active volcanos = ? – 20 erupting right now (50-60/year) (155/decade) • Number of volcanologists = 1,500 Lava flow Volcanic Eruptions • Nonexplosive Eruptions Lava fountain • Explosive Eruptions What is Lava? -magma that flows onto the Earth’s surface 1. What did you learn? Write/draw this in your science journal. Volcanoes form around Vents Lava vents that release magma onto the Earth’s surface. Magma chamber The Composition of Magma Determines whether it is explosive or not! • High content – More likely to be • High !!! content – More likely to be – Why? !!! • Silica has a thick, stiff consistency – Flows slowly – Tends to Harden in the volcano’s vent d.Blocky lava What Erupts from a Volcano? Lava can be thick or thin. a.Pahoehoe b.Aa Lava flows slowly, like wax-glassy surface with wrinkles Is cool, stiff lava that does not travel Far from the volcano Lava pours out quickly, forms a brittle crust with jagged edges c.Pillow lava Forms when lava erupts under water, round lumps What Erupts from a Volcano? Pyroclastic material • Rock fragments created by eruptions •magma explodes from volcano and solidifies in the air •existing rock is shattered by powerful eruptions Volcanic ash Forms when gas bubbles explode Volcanic bombsVolcanic blocksLargest pieces of solid rock erupted from volcano Large blobs of magma that harden in the air, shape is created by magma spinning in the air LapilliLittle rock- pebbel-like Bits of magma that harden before they hit the ground How do volcanoes affect the Earth? Flows and Fallouts • hot ash can flow really quickly •Knock down buildings •Dam rivers (flooding/drought) •Kill crops and livestock Climatic Changes •Ash & Gases can block sunlight •Drop average global temperature noticeably Types of Volcanoes Cinder cone volcanomade of pyroclastic material usually explosive, small and have short eruption times. Shield volcanobuilt by layers of flowing lava, with gently sloping sides Composite volcano also called stratovolcanoes are the most common type of volcanoes. They have Explosive eruptions that are a combinations of lava and pyroclastic material. Steep bases and sides. Shield Volcano • Is wide and somewhat flat. • It forms from a quiet eruption. • Lava flows out quietly and for great distances. Cinder Cone Volcano Has tall, very steep sides. Has explosive eruptions. This eruption produces a lot of cinder and ash. Composite Volcano Form from explosive eruptions. Produce a lot of lava and ash. Is small, with steep sides. Craters, Calderas, and Lava Plateau Crater • From explosions of material out of the vent and the collapse of material back into vent Caldera • Much larger depression that forms when magma chamber empties and its roof collapses Lava Plateau • Forms when lava erupts from long cracks, or fissures, and spreads out evenly (thousands of km) What causes volcanoes? The Formation of Magma • Mantle rock melts when the temperature increases or the pressure decreases. What causes volcanoes? Where Volcanoes Form • Tectonic Plate Boundaries!!! ~75% world’s active volcanoes in Ring of Fire What causes volcanoes? What causes volcanoes? Hot Spots How do volcanologists predict eruptions? • Measuring Small Quakes – Before eruption, increase in number & intensity • Measuring Slope – Bulges may form with magma (tiltmeter) • Measuring Volcanic Gases – Outflow of volcanic gases • Sulfur dioxide, carbon dioxide • Measuring Temperature from Orbit – Measure changes in temperature over time You should not be a Volcanologist if…. Robert McGimsey USGS A. Ozerov • You don’t like hiking, backbacking, rockclimbing, etc. • You are not interested in experiencing extreme temperatures and heights. • If you don’t like to travel to incredible places and see breathtaking views of the world.