Field interpretation of Volcanoes Field interpretation of Volcanoes ...
VOLCANOES
description
Transcript of VOLCANOES
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VOLCANOESVOLCANOESTheirTheir
ProductsProducts
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Types of Types of Lava Lava
Aa - blocky (no gas/viscous)Pahoehoe – ropy (fluid)
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MAGMA COMPOSITIONMAGMA 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
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ASH ASH CLOUDCLOUD
Mount St Helens, WashingtonPinatubo, Phillipines
Credit: U.S. Geological Survey Credit: U.S. Geological SurveyCredit: U.S. Geological Survey
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PyroclasticPyroclasticFlowFlow(Nuee(NueeArdente)Ardente)
Very hot (~1000 deg C)Ash and volatiles. Flows very fast.
Rock formed is anIgnimbrite ( egSnowdonia)
Credit: U.S. Geological Survey
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TEPHRATEPHRA
A general A general termtermto includeto includeash, lapilli,ash, lapilli,blocks &blocks &bombsbombs
Credit: U.S. Geological Survey
(Photographs: 1 - D E Wieprecht; 2 - C Heliker)
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Volcanic Ash – less than 2mmVolcanic Ash – less than 2mm
Lapilli – 2 to 64 mmLapilli – 2 to 64 mm
Volcanic bombs – more than 64mmVolcanic bombs – more than 64mm
Terms used to describe tephraTerms used to describe tephra
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Pumice – volcanic frothPumice – volcanic froth
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Some ‘volcanic’ termsthat you should become familiar with.
Credit: U.S. Geological Survey
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LAHARSLAHARS When pyroclastic debris gets mixed withwater (eg rain, melted ice or snow) it produces a fast flowing mud flow.This can be very destructive flowingdown valleys and submerging settlements.
Nevada de la Ruiz, Colombian Andes, 1985. The town of Armero, 50 km away, was engulfed, killing 25,000 people.Credit: U.S. Geological Survey
(Photographs: 1 – B Myers; 2 – JN Marso
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Mount St Helens Eruption, 1980 – photo sequence
Credit: U.S. Geological Survey
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Effect of blast from Mt St Helens
These trees were about 30 km away!
Credit: U.S. Geological Survey(Photograph by Lyn Topinka)
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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)
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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.
HYDROTHERMALEFFECTS
Credit: U.S. Geological Survey(Photograph : SR Brantley)
Geyser at Yellowstone National Park, Wyoming
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VOLCANIC GASESVOLCANIC GASES
Water vapour (70 – 95%) – origin of oceansCarbon dioxideSulphur dioxide
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Effect on ClimateEffect on ClimateGlobal 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’.
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I suggest that you go on I suggest that you go on the Internet and find some the Internet and find some of your own images. I got of your own images. I got most of these from Google most of these from Google (images).(images).