Volcanic activity
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Transcript Volcanic activity
Volcanic activity
PG. 89
Magma
Temperature beneath the lithosphere causes rock to
melt
As pressure increases, the melting point of rock
increases
At any pressure, a wet rock will melt at a lower temp
Types of magma
Magma formed from the 3 major types of igneous
rock- basalt, andesite, and granite
Major types of magma: basaltic, andesitic, and
rhyolitic
Hawaiian volcanoes- basaltic
Mt. St. Helens in Washington are andesitic
Dormant volcanoes in Yellowstone are rhyolitic
Mt. St. Helens
Magma composition
The viscosity of magma is based on silica content more
silica, higher viscosity
Basaltic magma
Volcanoes erupt quietly
About 50% silica
Made from rocks in the upper mantle
Oceanic and continental crust
Andesitic magma
found along subduction zones
Made from oceanic crust and sediments
60% silica, eruptions are in the medium range
Rhyolitic magma
Comes from water rich continental crust
Very explosive
70% silica content
Basaltic volcano
http://www.youtube.com/watch?v=5hE2DZdl0IA
Andesitic volcano
Rhyolitic volcano
Intrusive activity
When magma cools, it forms structures called plutons
Plutons are based on size and shape
Largest plutons batholiths and stocks; form beneath
earths surface; coarse rock
Laccoliths mushroom shaped pluton
Sills and dikes smallest pluton
Anatomy of a volcano
Magma erupts in an opening called a vent
Around the vent is a crater
Calderas can form when a volcano collapses into the
magma chamber
Types of volcanoes
Shield volcano
Mountain w/ broad gently sloping sides that forms when
basaltic rock is layered
Cinder cone volcanoes
Forms when material is ejected high in to the air and piles up
around a vent
Has steep sides
More explosive
Composite volcanoes
Much larger than cinder cone
Dangerous to humans
Lava alternates with volcanic fragments
Types
Shield
Cinder cone
Composite
Volcanic Material
Tephra- rock fragments thrown into the air
Can be dust, ash, lapilli, volcanic blocks, or volcanic
bombs
Rapidly moving volcanic material is called
pryoclastic flow
Volcano occurrences
Convergent volcanism
At a convergent boundary
Usually form in the sea
Divergent volcanism
Magma forced upward through faults
Causes seafloor spreading
Pg. 90
Create a foldable of the 3 different types of
volcanoes. Include a diagram of each on your
foldable ( look on pgs. 482-483 for diagrams)
Include the types of magma and how explosive it is