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VOLCANOES
Mount Fuji
Mauna Loa
Volcanic Landforms
Key concepts: Volcanic landforms vary with
- tectonic setting,
- composition of magma
-------- conditions during eruption,
- volume of eruption.
Types
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Shield
Composite
Fissure
Cinder
ShieldVolcanoes
large volcanoes with broad summit
areas and low-sloping sides
- low viscosity basaltic lava flows.
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A good example of a shield volcano is the Island of
Hawaii (the "Big Island").
Composite Volcanoes
-built by multiple eruptions, sometimes recurring over
hundreds of thousands of years, sometimes over a few
hundred.
-Andesite magma, the most common but not the only
magma type, tends to form composite cones.
- built mostly of fragmental debris,
- with a structural framework of dikes and sills that
knits together the voluminous accumulation of
volcanic rubble..
-Composite cones can grow to such heights that
their slopes become unstable.
Mayon
Mount Rainier
Mount Fuji
Cinder cones
Cinder cones are mounds of basaltic
fragments.
Streaming gases carry liquid lava
blombs into the atmosphere that rain
back to earth around the vent to form a
cone.
Calderas
 are
circular to oblong depressions formed by
collapse of the central vent during the extrusion
of pyroclastic materials.
Their diameters are many times larger than
those of associated vents.
Domes
Lava domes form by the slow extrusion
of highly viscous silica-rich magma
Domes can be solitary volcanoes, form
in clusters, grow in craters or along the
flanks of composite cones.
A dome has been growing slowly within
the crater of Mount St. Helens since the
eruption of 1980. Domes have also filled
the crater of Mt. Pelée, Martinique, etc.
List of Volcanic Hazards
Pyroclastic Density Currents (pyroclastic
flows and surges)
Structural Collapse: Debris flowAvalanches
Dome Collapse and the formation of
pyroclastic flows and surges
Lava flows
Tephra fall and ballistic projectiles
Volcanic gas
Tsunamis
Mount St Helens
1980