KINDS OF VOLCANIC ERUPTIONS – CHAPTER 3.3 (pp. 94-98) This section explains what happens when a volcano erupts and two types of volcanic eruptions. You will also identify a volcano’s stage of activity. Geologists classify volcanic eruptions as quiet or explosive Quiet Eruptions: a volcano erupts quietly if its magma is low in silica. How does the gases in magma bubble out? Gently or violently? ____________________ What is the type of island that is formed from quiet eruptions? ____________________ Explosive Eruptions: a volcano erupts explosively if its magma is high in silica. Where does the magma build up in the volcano and “plugs it up” like a cork? ____________ What is trapped inside a volcano and cannot escape from the thick magma? ______________ Steam and gases push magma out of the volcano with incredible force. __________________ What mountain violently erupted in Washington State in 1980? _________________________ Pyroclastic flow: occurs when an explosive eruption hurls out a mixture of hot gases, cinders, cinders and bombs. Look at the Power of Volcanoes on pages 96-97 List the major volcanic eruptions, where they occurred and what kind of flow they were: 1883: ____________________________________________ 1902: _____________________________________________ 1912: _____________________________________________ 1980: _____________________________________________ 1991: _____________________________________________ 2002: _____________________________________________ Monitoring Volcanoes: (p. 98) Geologists predict volcanic eruptions by using tiltmeters. The tiltmeters measure gases escaping from the volcano and temperature increases in underground water. They also monitor earthquakes that occur around the volcano. 1. Draw and Describe the surface of obsidian. DESCRIBE Obsidian Rock: DRAW Obsidian The surface of obsidian is smooth and glossy Obsidian formed when lava cooled very quickly Magma Reaches Earth’s Surface (p. 91-93) 2. Where does lava come from? Lava begins as magma, which forms in the asthenosphere. The materials in the asthenosphere are under great pressure. As magma rises, it flows upward into cracks in the rock above. But, if an opening in weak rock allow the magma to reach the surface, a volcano forms. 3. Label the drawing with the following terms: Magma chamber – magma collects in this pocket Pipe – a long tube in the ground that connects the magma chamber to Earth’s surface Vent –molten rock and gas leave the volcano through this opening Crater – a bowl shaped area at the top of the volcano that may form around the vent 4. What is lava flow? The area covered by lava as it pours out of a vent.