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Prepared by Srusti Abinash Puri & Umakanta , Class VII Guided by Mr. Deepak Kumar TGT(S.St) What is Volcano? Fissure or vent through which molten rock material, or magma, and gases from the interior of the Earth erupt on to its surface, and the landform which is produced as a result of this eruption is known as volcano. A. Structure of volcano 1. Volcanoes contain a vent, crater and slopes. 2. A vent is an opening in the crusts surface in which lava is emitted. 3. A crater is connected to the magma chamber that is located near the vent. B. What is a caldera? 1. A caldera is sometimes confused with a crater. 2. They differ in size. 3. A caldera is around 50 km in diameter, while a crater is at most 1 km in diameter. C. How is a caldera formed? 1. A caldera is formed when the slopes of a volcano collapse. 2. The top of the magma chamber becomes empty from lava flow. 3. The caldera then fills up with water forming a lake. Main Idea: Types of Volcanoes A. How does a Shield volcano form? 1. 2. 3. They form when layers of lava accumulate over time. The eruptions are slow and nonexplosive. Shield volcanoes are the largest in size. B. How does a Cinder-Cone volcano form? 1. They form when lava is ejected high into the air and piles up around the vent. 2. Small in size less than 500 m high. 3. More explosive than shield volcanoes, because magma contains more water and silica. 4. Magma is more viscous, which leads to more gas C. How do Composite-Cone volcanoes form? 1. These volcanoes form when layers of lava alternate with layers of volcanic fragments (ash, tephra). 2. Larger than cindercone 3. Are the most dangerous of all volcanoes D. Where on earth can volcanoes be found? 1. 2. 3. 4. Volcanoes are found along plate boundaries. 80 % on convergent boundaries 15 % on divergent boundaries 5 % occur away from plate boundaries E. Hot spots 1. 2. 3. Areas on Earth’s mantle where high temperature causes sections of earth to rise (Hawaii). The heat melts the rock, which is forced to the surface as magma. The magma melts the crust forming volcanoes.
