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Section 2: Volcanic Activity Friday, March 12, 2010 Pages 183 -- 192 Arenal Volcano -- Costa Rica Objectives • Describe what happens when a volcano erupts. • Explain how the two types of volcanic eruptions differ depending on the characteristics of magma. • Identify some hazards of volcanoes • Identify types of volcanic activity other than eruptions. Vocabulary Words • • • • • • • Magma chamber Pipe Vent Lava flow Crater Silica Pahoehoe • • • • • • • • Aa Pyroclastic flow Active Dormant Extinct Hot spring Geyser Geothermal energy Origin of Magma • Lava begins as magma in the mantle. • The magma is under great pressure • Magma flows upward because it’s less dense than surrounding materials. • Magma will continue to rise until it reaches the surface or until it becomes trapped beneath rock. Volcanic Eruptions • The trapped gases found in magma are under great pressure. – Ex: soda bottle • As the magma reaches the surface, the pressure decreases. • The gases begin to separate out, forming bubbles. • During volcanic eruption, the gases dissolved in the magma rushes out, carrying the magma with them. Stromboli -- off the North coast of Sicily. Exploring a Volcano Dust Cloud Crater Vent Pipe QuickTime™ and a decompressor are needed to see this picture. Side Vent Lava Flow Lava Magma Magma Chamber Characteristics of Magma • There are many types of magma. – Some are thick and flows slowly. – Some are fluid and flow very easily. – The temperature of the magma will determine how it flows. The Role of Silica • The amount of silica in magma also helps to determine how easily the magma flows. • What is silica? – It’s a material formed from 2 different elements -- oxygen and silicon. – There are lots of silica found on the Earth’s crust and mantle. The Role of Silica -- Cont’d • The more silica magma contains, the thicker it is. • Magma with a lot of silica produces lightcolored lava. • Rhyolite is an example of a rock formed from magma with lots of silica. QuickTime™ and a decompressor are needed to see this picture. Rhyolite Role of Silica -- Cont’d • Magma that is low in silica flows easily and produces darkcolored lava. • Basalt is an example of a rock with very little silica. QuickTime™ and a decompressor are needed to see this picture. Types of Volcanic Eruptions • The type of magma that flows from a volcano will determine whether the eruption is quiet or explosive. Quiet Eruptions • If the magma flows easily, the eruption will be quiet. • This is because the gases in the magma bubble out slowly. • The lava is usually thin and runny. • There are 2 types of lava produced this way. – Pahoehoe – aa Pahoehoe • Fast moving • Looks wrinkled, rope-like QuickTime™ and a decompressor are needed to see this picture. aa QuickTime™ and a decompressor are needed to see this picture. • This type of lava is cooler. • It is slower-moving. • When cooled, the surface is jagged and chunky. Explosive Eruptions • Eruptions are explosive if the magma is thick and sticky. • The thick magma prevents the lava from flowing freely. • Instead, the magma builds up slowly in the pipe and acts as a plug. • The trapped gases build up until it explodes. Explosive Eruptions -- Cont’d • The lava is pushed out violently. • The lava is broken into fragments that cool quickly. – Can be as small and fine as volcanic ash – Can be as large as a car • This type of flow is called pyroclastic flow. Mount St. Helen • This is an example of pyroclastic flow. QuickTime™ and a decompressor are needed to see this picture. Stages of a Volcano • Active – The volcano is alive. • Dormant – The volcano is asleep. • Extinct – The volcano is unlikely to erupt again. Other Types of Volcanos • Hot Springs QuickTime™ and a decompressor are needed to see this picture. Mt. Princeton Hot Springs, CO – Formed from the heating of underground water by a nearby body of magma – This water may contain dissolved gases and other substances found deep within the Earth. Other Types of Volcanos • Hot Springs QuickTime™ and a decompressor are needed to see this picture. Mt. Princeton Hot Springs, CO – Formed from the heating of underground water by a nearby body of magma – This water may contain dissolved gases and other substances found deep within the Earth. Other Types of Volcanoes QuickTime™ and a decompressor are needed to see this picture. Old Faithful -- Yellowstone • Geyser is a fountaiin of water and steam that erupts from the ground. • This is a result of water and steam that is trapped underground. Geothermal Energy • This is a form of alternative energy. • This form of energy is clean and reliable. • Is energy source is used in Iceland, northern California and New Zealand. Homework • Workbook 6.2 (3/15) • Vocabulary quiz 6.2 (3/17) • Workpacket 6.2 (3/17)