EAS100 Lecture Notes - Lecture 11: Tephra, Pyroclastic Flow, Stratovolcano

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EAS 201: Lecture 11
January 30, 2019
Slide information borrowed from Karlis Muehlenbachs January 30,
Image taken from Karlis Muehlenbachs slides January 30, 2019.
o Can be classified by location Subaerial (under air),
Submarine, or Subglacial.
o Classified by shape Shield Volcano, Tephra Cone, or
o Other volcanic landforms include Calderas & Fissure
Shield Volcanoes: broad, roughly dome-shaped, basaltic.
o Biggest by size, but w/ surface slopes of only 5-10 degrees.
Tephra Cones & Stratovolcanoes:
o Rhyolitic & andesitic eruptions tend to eject a lot of
pyroclasts = steep-sided volcanoes (tephra rock
fragments/particles ejected by eruption).
o The bigger stratovolcanoes are steep cone-shaped
mountains made of layers of lava & tephra.
Volcanic Disasters:
o Hazards form stratovolcano eruptions occur as:
Hot, fast moving nuee ardentes (fast moving cloud of hot gases) & lateral
blasts aka “pyroclastic flow”.
Tephra & hot poisonous gases bury/suffocate.
Tephra + rain = lahar (deadly mudflow).
Violent undersea eruptions cause tsunamis.
Tephra destroys agricultural land as well as cities.
o Classification by activity
Active erupted in recent history.
Dormant no historic eruptions, not badly eroded.
Extinct no historic eruptions and is badly eroded.
o Precursors
Seismic activity, steam forming/temp changes.
Bulging, tilting or uplift.
Gas emissions around a volcano.
o Beneath every volcano, complex of chambers & channels that magma moves
through as it goes towards the surface.
o The chambers are filled w/ igneous rock.
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