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Volcanoes Chapter 9 Sections 1,2 and 3 VOLCANOES Slide 2 A. What is a volcano? 1.An area of the Earths surface through which molten material, or magma, and volcanic gases pass. Magma- molten mixture of rock- forming substances, gases & water from the mantle Lava- Magma that reaches the surface 3. 75% of the volcanoes in the world are located in the Ring of Fire. Slide 3 2. Most are located at plate boundaries. 3. 75% of the volcanoes in the world are located in the Ring of Fire. Ring of Fire Slide 4 A circular pattern located around the pacific ocean along the plate boundaries where volcanoes are more common What is the Ring of Fire? Slide 5 Where are volcanoes located? Volcanoes can be found: Diverging Plate boundaries (mid-ocean ridge) Converging plates with subduction zones Oceanic plate vs. oceanic plate Oceanic plate vs. continental plate Hot spotsHot spots Area where magma from deep within the mantle melts through the crust like a blow torch Example: Hawaiian IslandsHawaiian Islands Slide 6 Eruptions Why do volcanoes erupt? Less dense magma seeps upward through cracks and creates volcanoes Gas in the magma is trapped and builds pressure Closer it gets to surface the less pressure it has and the gases separate (bubbles) Gases dissolve on the surface and magma is carried out Types of eruptions Quiet lava moves steadily and easily Explosive explodes and releases lave flow Slide 7 Stages of a Volcano Active: (live) erupting or has shown signs that it may erupt In the near future Dormant: (Sleeping) is not currently erupting but may/can erupt in the future Extinct: (dead) unlikely to erupt again Slide 8 3 Types of Volcanoes 3 Types of Volcanoes 1. Shield Volcano 2. Cinder Cone Volcano 3. Composite Volcano Slide 9 Shield Volcano 1. Produced by: a. layers of lava released from non- explosive eruptions. b. lava spreads out over a wide area. c. created by hot spots 2. These volcanoes have: a. gently sloping sides. b. lava spreads out over a wide area. 3. Shaped like a shield Mount Kea, in Hawaii, is the largest volcano on Earth. Measured from its base on the sea-floor, it is taller than mount Everest. Slide 10 Shield Volcano Here are 4 of the volcanoes that comprise the big island of Hawai'i. They are Mauna Kea (MK), Mauna Loa (ML), Hualalai (H), and Kohala (K). The photo was taken from near the summit of East Maui volcano (EM). These are the largest volcanoes on Earth. Slide 11 Slide 12 Slide 13 Slide 14 Slide 15 Slide 16 Slide 17 Slide 18 Slide 19 Shield Volcano Belknap Shield Volcano in Oregon. Slide 20 Cinder Cone Volcanoes 1.Produced from: a. moderately explosive eruptions. 2. Cinder cone volcanoes: a. have steep slopes. b. are usually small. c. often occur in clusters. d. cone shaped hill/mountain Slide 21 Cinder Cone Volcano Veniaminof, AlaskaMount Etna, Italy Slide 22 Slide 23 Slide 24 1. Composite Volcanoes a. form from alternating explosive and non- explosive eruptions. b. broad bases and sides that get steeper toward the top. c. most common d. alternating layers of ash and lava Composite Volcanoes Slide 25 Mount Ranier, Washington Slide 26 Slide 27 Slide 28 Slide 29 Slide 30 Slide 31 Slide 32 Costa Rica- Arenal Volcano http://www.arenal.net/arenal-volcano.htm Slide 33 Slide 34 F. What is a crater? 1.The area around the central vent of a volcano is called a crater. Slide 35 http://www.serve.com/wizjd/parks/crater_lake/crater_lake.html More pics of Crater Lake: Slide 36 Slide 37 Slide 38 Slide 39 Slide 40 Slide 41 What is a Hotspot? 1.an area of persistent volcanic activity. 2. originate at unusually hot areas of the mantle- core boundary. 3. Overlying mantle melts forming plumes of magma that rise and penetrate the crust forming volcanoes. 4. Hawaii, Iceland, and Yellowstone are examples of hot spots.