Volcanic Landforms
Volcanic Landforms
• Erupted onto the surface.
• Relief created by buildup of lava flows and
pyroclastic deposits (tephra).
• Constructional landforms.
Types of Volcanic Lavas
• Basaltic - melting in the upper mantle.
– very hot
– very fluid - low viscosity
• Andesitic - melting of lower lithosphere
mixed with water.
– more viscous, gas-rich
• Dacitic / Rhyolitic - melting of continental
crust.
– highly viscous, silica-rich
– All of the above (wherever crust is heated).
Shield Volcano
Basaltic Lava
Relative size
Stratovolcano or
Composite Volcano
Andesitic Lava
Calderas
• Large, crater-like depression created by the
collapse of a volcano into its own magma
chamber.
• Associated with both shield and
stratovolcanoes.
Shield Volcanoes
• Very large, low relief
• Hawaiian Islands, Galápagos Islands
• Basaltic lava, high volume
Flood basalts
• Repeated eruption of fluid basaltic lava over
large areas from fissures and shield vents.
• Hasn’t happened in human history.
• Columbia River plateau, Idaho / Washington
(Tertiary)
• Watchung Mts., New Jersey (Early Jurassic)
• Deccan Traps, India (Late Cretaceous)
• Siberian Traps (Permian)
Stratovolcanoes
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Steep, high relief
Andesitic and dacitic magmas
Explosive eruptions
Associated with subduction zones
Lava Domes and Coulees
• Mass of very viscous, rhyolitic or glassy lava.
• May form a plug dome above a volcanic vent.
• Coulee - cross between a lava dome and a lava
flow - viscous mass of lava that can flow
downslope.
Cinder Cone / Tuff Cone Volcanoes
• Built from lava fragments ejected from a
single vent.
• Roughly symmetrical in shape, asymmetry
may be due to prevailing winds.
• App. 30° slope dictated by angle of repose of
cinder.
• Tuff produced by reaction of lava and water,
resulting in phreatic (steam) explosions.