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CO: VOLCANOES LO: Describe the types of volcanoes, which type of plate boundaries create volcanoes and why volcanoes occur there

Dec 13, 2015




  • Slide 1

CO: VOLCANOES LO: Describe the types of volcanoes, which type of plate boundaries create volcanoes and why volcanoes occur there. Slide 2 DEFINITIONS VOLCANO - IS A MOUNTIAN FORMED WHEN MAGMA FROM THE MANTLE RISES TO THE EARTHS SURFACE. MAGMA-IS MOLTEN ROCK THAT IS BENEATH THE EARTHS SURFACE. LAVA- IS MOLTEN ROCK THAT IS ON OR ABOVE THE EARTHS SURFACE. Slide 3 HOW A VOLCANO FORMS 1.Magma starts to rise to the Earths surface because it is less dense than the surrounding rock. 2.The magma works its way to the surface through cracks (known as faults) in the Earths crust. 3.Once the magma reaches the surface a volcano is formed. Slide 4 1.DIVERGENT PLATE BOUNDRIES 2.CONVERGENT PLATE BOUNDRIES 3.HOT SPOTS Slide 5 DIVERGENT PLATE BOUNDARY VOLCANO At divergent boundaries crustal plates form deep cracks called rifts. Magma rises to the surface through these rifts. This occurs along mid- ocean ridges and within continents EXAMPLE: The Edfel Volcano on the island of Iceland. Slide 6 Slide 7 Edfel Volcanic eruption in 1973 Slide 8 CONVERGENT PLATE BOUNDARY VOLCANOES At convergent boundaries magma that forms in the subduction zone rise to the surface through weaknesses or cracks the earths crust, forming a volcano. Mt. Shasta in California is a convergent boundary volcano. So is Mt. Saint Helens. Slide 9 Slide 10 The Cascade Mountain Range in the Pacific Northwest features several active and dormant volcanoes. These volcanoes formed over the subduction zone where the Juan de Fuca plate meets the North American plate Slide 11 Slide 12 Slide 13 HOT SPOT VOLCANOES Hot spots are place where the mantle is hotter than the rest of the mantle. Volcanoes form when magma from these spots rises to surface. Hot spots can occur in the middle of tectonic plates. Hawaiian islands formed over a hot spot. Yellowstone also is on top of a hot spot. Slide 14 PACIFIC RING OF FIRE Most of the worlds active volcanoes occur at the plate boundaries that surround the pacific ocean. This forms a circle known as the pacific ring of fire. Slide 15 VOLCANOES (PART 2) Slide 16 TYPES OF ERUPTIONS Volcanic eruptions range from violent and explosive to relatively quiet. Two factors effect this: 1) Composition of the magma. ( how much silica is in the magma) 2) How much gas is trapped in the volcano Slide 17 Composition of the Magma BASALTIC MAGMA (MAFIC)- the more basaltic the magma is the smoother it flows and the more quiet the eruption. GRANITIC MAGMA (FELSIC) - is thick and does not flow easily. Granitic magma plugs up the vent of the volcano allowing pressure to build. When the pressure becomes to great an explosive eruption results Slide 18 TYPES OF VOLCANOES SHEILD VOLCANOES CINDER CONE VOLCANO COMPOSITE (Strato) VOLCANO Slide 19 SHEILD VOLCANOES Broad base and gentle slopes Form as a result of quiet eruptions of basaltic (runny) magma. Hawaiian volcanoes are examples Slide 20 Slide 21 Slide 22 CINDER CONE VOLCANOES Form from explosive eruptions. Steep slopes of tephra and ash. Slide 23 Slide 24 Slide 25 Slide 26 Slide 27 COMPOSITE CONE VOLCANOES Form from combinations of explosive and quiet eruptions Steep slopes made of alternating layers of tephra and lava. Highest of all volcanoes Slide 28 Slide 29 Slide 30 Colima in Mexico Slide 31 Mount Hood in Oregon Slide 32 Mount Rainier in Washington State Slide 33 Mount Shasta in Northern California Slide 34 Mount St. Helens and Spirit Lake before the 1980 Eruption Mount St Helens and Spirit Lake in 1982 Slide 35 Mt. St. Helens Slide 36 Mt. Saint Helens Slide 37 Slide 38 Slide 39 More than 50 volcanoes in the United States have erupted one or more times in the past 200 years. The most volcanically active regions of the Nation are in Alaska, Hawaii, California, Oregon, and Washington. Volcanoes produce a wide variety of hazards that can kill people and destroy property. Large explosive eruptions can endanger people and property hundreds of miles away and even affect global climate. Some of the volcano hazards, such as landslides, can occur even when a volcano is not erupting. -- Myers,, 1997