Volcanoes and Other Igneous Activity
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True or False: Basalitic Magmas contain less silica than granitic magmas
True
Mafic Magmas created through the__
melting of mantle rocks
Mafic magmas contain (high/low gas content and are they fluid)
low gas content; very fluid
Basalitic Magmas
Lowest silica content; Lowest Gas content; lowest viscosity; erupt at highest temperatures
Granite/Rhyolitic Magmas
Very viscous, high gas content and high silica content; erupt at the lowest temperatures
Where do mafic magmas erupt from ___
Sea floor at divergent boundaries
Continental Settings of Mafic Magmas
Mafic magma travels upwards and less dense magmas of andesitic or rhyolitic composition continues the journey upwards
Factors affecting viscosity
silica content; gas content; temperature
More silica =
more viscous
Higher gas content =
more viscous
Andesitic Magma:
Intermediate silica content, gas content, viscosity, and temperature
Effusive eruptions
Very fluid basalitic lavas
Explosive eruptions
eruption columns of volcanic ash and gases
Two types of lava flows:
Aa and Pahoehoe flows
Aa flows
Spiny and jagged; low temperatures
Pahoehoe flows
ropes and braids; can transition into aa flows; higher temps
Lava tubes
created by pahoehoe flows which is a cave-like tunnel with a hardened exterior
Pillow lavas
Hardened outer skin w/ a small hole that squeezes out lava like toothpaste to form more “pillows”. (Occurs on the sea floor at divergent boundaries)
Most of Earth’s volcanic output occurs at ____ boundaries
divergent
Volatiles
various amounts of dissolved gases
Pyroclastic materials also known as ___
tephra
Tephra particle sizes from G-L
Volcanic blocks, volcanic bombs, cinders (lapilli), volcanic ash
Shield volcanoes are formed from
accumulation of fluid basaltic magmas
Shield volcanoes originate as __
seamounts