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VOLCANOES

VOLCANOES. Their Products. Types of Lava . Aa - blocky (no gas/viscous) Pahoehoe – ropy (fluid). MAGMA COMPOSITION. ‘Acidic’ – high silica, low temperature (~ 800 deg C), viscous. eg Andesite, Rhyolite Gases are trapped, violent explosions, pyroclastics.

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VOLCANOES

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  1. VOLCANOES Their Products Peter Copley Feb 04

  2. Types of Lava Aa - blocky (no gas/viscous) Pahoehoe – ropy (fluid) Peter Copley Feb 04

  3. MAGMA COMPOSITION ‘Acidic’ – high silica, low temperature (~ 800 deg C), viscous. eg Andesite, Rhyolite Gases are trapped, violent explosions, pyroclastics. ‘Basic’ – low silica, high temperature (~ 1200deg C), fluid. eg Basalt Gases can escape, gentle eruptions, lava Peter Copley Feb 04

  4. ASH CLOUD Mount St Helens, WashingtonPinatubo, Phillipines Credit: U.S. Geological Survey Credit: U.S. Geological Survey Credit: U.S. Geological Survey Peter Copley Feb 04

  5. PyroclasticFlow(NueeArdente) Very hot (~1000 deg C) Ash and volatiles. Flows very fast. Rock formed is an Ignimbrite ( eg Snowdonia) Credit: U.S. Geological Survey Peter Copley Feb 04

  6. 1 TEPHRAA general termto includeash, lapilli,blocks &bombs 2 3 Credit: U.S. Geological Survey (Photographs: 1 - D E Wieprecht; 2 - C Heliker) Peter Copley Feb 04

  7. Volcanic Ash – less than 2mm Terms used to describe tephra Lapilli – 2 to 64 mm Volcanic bombs – more than 64mm Peter Copley Feb 04

  8. Pumice – volcanic froth Peter Copley Feb 04

  9. Some ‘volcanic’ terms that you should become familiar with. Peter Copley Feb 04 Credit: U.S. Geological Survey

  10. When pyroclastic debris gets mixed with water (eg rain, melted ice or snow) it produces a fast flowing mud flow. This can be very destructive flowing down valleys and submerging settlements. Nevada de la Ruiz, Colombian Andes, 1985. The town of Armero, 50 km away, was engulfed, killing 25,000 people. LAHARS Credit: U.S. Geological Survey (Photographs: 1 – B Myers; 2 – JN Marso 1 2 Peter Copley Feb 04

  11. Peter Copley Feb 04

  12. Mount St Helens Eruption, 1980 – photo sequence Credit: U.S. Geological Survey Peter Copley Feb 04

  13. Effect of blast from Mt St Helens These trees were about 30 km away! Credit: U.S. Geological Survey (Photograph by Lyn Topinka) Peter Copley Feb 04

  14. Peter Copley Feb 04

  15. A Caldera Caused by the collapse of a volcano into its magma chamber. This one is several miles across. Credit: U.S. Geological Survey (Photograph by M Williams) Peter Copley Feb 04

  16. HYDROTHERMAL EFFECTS A Geyser (from the Icelandic – Geysir). Water moves down to the hot rock or magma which turns to superheated steam. When the pressure is sufficient it rapidly expands and reaches the surface as a column of very hot water and steam. Geyser at Yellowstone National Park, Wyoming Credit: U.S. Geological Survey (Photograph : SR Brantley) Peter Copley Feb 04

  17. VOLCANIC GASES Water vapour (70 – 95%) – origin of oceans Carbon dioxide Sulphur dioxide Peter Copley Feb 04

  18. Effect on Climate Global Warming – most volcanic gases produce a greenhouse effect. Global Cooling – pyroclastic debris can block out the Sun. 1992 – Pinatubo a 0.5 deg C drop 1815 – Tambora (Indonesia) ‘the year without a summer’. Peter Copley Feb 04

  19. I suggest that you go on the Internet and find some of your own images. I got most of these from Google (images). Peter Copley Feb 04

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