Flashcards
Volcanoes
Cards in this deck (34)
- 1What are volcanoes built up by?Accumulation of their eruptive products:
. Lava
. Volcanic bombs (chunks of lava)
. Tephra (airborne ash and dust) - 2What other materials are erupted apart from the previously mentioned?. Lapilli (small stones)
. Mudflows (lahars)
. Pyroclastic flow - 3What is pyroclastic flow?Fast moving cloud of superheated gas and rock which reaches speeds moving away from the volcano of up to 700 km/h
- 4What happens when the magma reaches the vent?Magma froths in vent and creates gas bubbles which explode and shatter the lava
- 5What does the flow do when on the ground?. The flows normally hugs the ground and travel downhill, or spread laterally under gravity
. They are common and devastating result go explosive eruptions - 6What are volcanoes?Volcanoes are commonly conical hills or mountains built around a vent connected to reservoirs of molten rock below the earth’s surface.
- 7How many volcanoes are there in the world?. Approx. 1500
. Only small amount erupting at once
. Some volcanoes e.g. Hawaii erupt more or less continuously but others lie dormant
. Extinct volcanoes have not erupted for 25,000 years - 8What does the nature of volcanic landforms depend on?. How viscous the lava is when it reaches the Earth's surface
. Only a tiny proportion of the magma which forces its way upwards through the crust is extruded not the earth’s surface of lava - 9Silica content of: . Basaltic lava . Andestic lava . Rhyolitic lava. Basaltic lave= basic lava 45-52% silica content
. Andesitic lava= acid lave 52-66% silica content
. Rhyolitic lava= 66-75% silica content - 10Basaltic lava: . viscosity . temperature . cooling and solidifying. Low viscosity
. Hot 1200- hottest lava there is
. Takes longer time to cool and solidify so flows longer distances as river of molten rock - 11Basaltic lava: . Landforms . Lava . Eruptions . Location. Produces extensive but gently sloping landforms, lava plateaus
. Eruptions frequent but more gentle
. Lava and steam ejected
. Constructive margins e.g. fissures along Mid-Atlantic Ridge (Heimaey), over hotspots (Mauna Loa, Hawaii) - 12Basaltic lava: . Iron? .Gases? . Special features. Rich in iron and magnesium, quite runny
. Gases escape easily, not much ash
. 'Pillow lava' forms when basaltic lava erupts under water/ice, when lava is exposed water/ice quickly chills outer layer. Moltern lava beneath chilled surface eventually break through skin and process is repeated= resulting pile of lava pillows - 13Andesitic lava: . Viscosity . Temperature . Cooling and solidfying. Viscous
. Less hot, 800
. Soon cools and solidifies, flows very short distances - 14Andesitic lava: . Landforms . Eruptions . Ash, rock and gases. Produces steep-sided more localised features
. Eruptions are less frequent but more violent as build up of gases- generally form composite volcanoes
. Ash, rock, gases, steam and lava ejected - 15Andesitic lava and rhyolitic: . Location. A= destructive margins where oceanic crust is subducted, melts and rises, e.g. subducted zones Mt St Helens, e.g.Island Arcs Mt Pelee Martinique, e.g. Andes (Andesitic)
. R= often found at destructive and collison margins - 16Rhyolitic lava: . Viscosity . Temperature . Explosivity . Volcanoes. Highly visas lava that can just barely flow
. Less hot 700-1200
. Very explosive due to trapped gas bubbles
. Such lavas usually produce a volcanic dome that eventually is destroyed in a massive explosion as the viscous lava tries to escape - 17Fissure volcano: . Features . Rock type. No central crater or vent, instead giant cracks open in the ground and expel vast quantities of lava
. Basaltic - 18Fissure volcanoes: . Location . Nature of eruption. Constructive margins and rifts e.g. N. African
. Occur where longed crack in crust allows lava to spill out over a large area - 19Fissure volcanoes: . Named examplesHeimaey, Iceland, 1973. When Eurasian and N.American plate pulled apart, existing topography was drowned in a vast lake of basaltic lava, fissure 2km long
- 20Shield volcanoes: . Features . Rock type. Gentle sloping cones from layers of less viscous lava, tall and broad, large craters at their summits, built on thousands of outpourings of lava, quite frequent
. Basaltic - 21Shield volcanoes: . Location . Nature of eruption. Hot spots and where oceanic crust meet oceanic crust and constructive margins
. Gentle, predictable, lava flows out of central vent, lack explosivity. - 22Shield volcanoes: . Named examplesLargest volcano in the world, Mauna Loa in Hawaii, stands 4,170m above sea level with volume of 40,000km
- 23Composite volcanoes: . FeaturesCommonly found on land, created by layers of ash from initial explosive phases of eruptions and subsequent layers of lava from the main eruption phases.
Very common. Tall, symmetrically shaped, steep sides some 10,000 feet high - 24Composite volcanoes: . Rock type . Location . Nature of eruption. Andesitic
. Destructive margins
. Explosive, unpredictable, often vent becomes blocked by viscous lava and pressure builds, can create secondary cones.
Pyroclastic material, ash clouds, volcanic bombs - 25Composite volcanoes: . Named examplesMount Etna and Vesuvius in Italy, and Popocatepetl in Mexico.
Mount Fuji in Japan.
Mount St. Helens - 26Acid/dome volcanoes: . Features. Steep-sided volcanoes formed by very viscous lava. Lava cannot travel far, it builds up convex cone shaped volcanoes. Lava may solidify in the vent and be revealed by later erosion.
Can have central spine if lava solidifies in vent and is pushed up. Can form other volcanoes. - 27Acid/dome volcanoes: . Rock type . Location . Nature of eruption . Named examples. Rhyolitic
. Continental crust
. Explosive, unpredictable, pyroclastic flow and ash clouds
. Puy de Domes in France.
Mt Pelee - 28Acid-cinder volcanoes: . Features . Rock type. Simple volcanoes which have a bowl-shaped crater at the summit and steep sides. Smaller than composite, only grow to 1000 feet.
. Andesitic and basaltic - 29Ash-cinder volcanoes: . Location . Nature of eruption . Named examples. Destructive plate boundaries e.g. W coast of N America. Constructive margins- Iceland.
. During eruptions blobs (cinders) of lava are blown into the air
. Particularly in Mexico. Also in Crater Lake Oregon Surtsey, Iceland - 30Caldera volcanoes: . Features. Form when gases that have built up beneath a blocked volcanic vent results in a catastrophic eruption that destroys the volcano summit, leaving enormous crater where later eruptions may form smaller ones.
Surrounding land collapses into old magma chamber and leaves enormous crater surrounded by a higher caldera rim. - 31Calder volcanoes: . Rock type . Location . Nature of eruption. Andesitic/ rhyolitic
. Destructive margins
. Very explosive, unpredictable.
Very viscous lava with lots of trapped gas.
Lots of ash. - 32Calder volcanoes: . Named examples.Crater Lake in US, caldera has filled with water.
Krakatoa in Indonesia and Thera/Santorini in Greece, the sea has inundated the broken remnants of the volcano.
Yellowstone, USA - 33Volcanic explosivity index: . when created . What does it provide? . What determines the explosivity value. 1982
. Provides a relative measure of the explosiveness of volcanic eruptions
. Volume of products, eruptions cloud height, and qualitative observations (using terms ranging from gentle to mega-colossal) are used to determine the explosivity value - 34Volcanic explosivity index: . Is the scale open-ended or close-ended? . What is a typical value . What is it similar to. The scale is open-ended with the largest volcanoes in history given magnitude 8. A value of 0 is given for a non-explosive eruption.
. Typical will be between 4 and 6
. Very similar to Rickar Scale, it is logarithmic
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- A2 A2 Geography (Tectonics) Flashcards on Volcanoes, created by Alice Kimpton on 17/11/2016.
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- Alice Kimpton
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