volcano notes
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Transcript volcano notes
Ch. 6 Volcanoes
Volcanoes
A volcano is a weak spot in the
crust where magma comes to the
surface
Magma is molten rock, gases, and
water from the mantle
Magma becomes lava when it
comes to the surface
Lava cools to become igneous rock
Types of Rock
Igneous- molten material, such as
lava or magma, cools and hardens
Slow cooling- large crystals (granite)
Fast cooling- small crystals (basalt)
Metamorphic- great heat and
pressure changes minerals or
other rock
Heat and pressure increases inside
the Earth
Types of Rock
Sedimentary- sediment squeezed
and glued together
Sediment- small pieces of rock or
fossils that have been broken down
by erosion or weathering
The Rock Cycle
The rock cycle slowly builds,
destroys, and changes rock
Continuous and many pathways
The Rock Cycle
Volcanoes and Plate Tectonics
Volcanic belts are found at plate
boundaries, such as the Ring of
Fire around the Pacific Plate
Volcanoes and Plate Tectonics
Divergent boundaries- magma
comes out of rift valleys to build
mountains
Convergent boundaries
Oceanic plate sinks
Rock on top melts and becomes magma
Magma erupts and becomes lava
Volcanoes at Plate Boundaries
Hot Spots
Hot spots- volcanoes that form when
magma erupts through crust to get
to the surface
Hawaii
Yellowstone National Park
Parts of a Volcano
Magma
chamber-collects
magma
Pipe- tube that
connects magma
chamber to
surface
Vent- opening on
the Earth’s crust
Parts of a Volcano
Lava flow- area
covered by lava
Crater- bowlshaped area around
a volcano’s central
vent
Caldera- large
circular depression
formed when
magma chamber
empties and the
roof collapses
Eruptions
Pressure and gases force magma out
of a volcano
Silica makes magma thick and sticky
Types of eruptions
Quiet eruptions- lava oozes to surface
Thin, runny lava that is low in silica
Hawaiian Islands
Examples are pahoehoe and aa
Eruptions
Types of eruptions
Explosive eruptions- thick and sticky
lava which traps water
Water makes eruptions more explosive
Produces pyroclastic material
Magma that erupts as fragments of molten
material and solidifies in the air
Pieces of volcano that breaks off
Mt. St. Helens in 1980
Life Cycle
Geologists determine how likely a
volcano will erupt again
Stages
Active- erupting or will erupt in the
near future
Mt. Shasta and Lassen Peak
Dormant- “sleeping,” but can become
active again
Long Valley in eastern Sierras
Extinct- unlikely to erupt again
Diamond Head in Honolulu
Volcanic Landforms
Made of lava, ash, and other
materials
Types of Volcanoes
Shield Volcano- made from
nonexplosive eruptions
Low in silica
Wide with gentle slopes
Cinder Cone- made from explosive
eruptions
High in silica
Steep, cone-shaped, found in clusters
Volcanic Landforms
Types of Volcanoes
Composite- alternating layers of
pyroclastic material and lava flow
Also known as stratovolcano
Most common
Volcanic Landforms
Lava Plateaus- lava flows out of long
cracks called fissures
Thin, runny lava flows far before
cooling
Shield VolcanoMedicine Lake, CA
Cinder Cone VolcanoMt. Bromo, Indonesia
Composite VolcanoMt. Shasta, CA
Lava PlateauModoc Plateau, CA
Magma Landforms
Formed when magma goes into
cracks, but does not come to surface
Magma cools underground
Erosion exposes harden magma
Magma Landforms
Types
Volcanic Necks- magma hardens in pipe
Dikes and sills- magma cools between
rock layers
Igneous intrusions
Sill are horizontal
Dikes cross rock layers
Batholiths- massive rock forms when
large body of magma cools
Magma Landforms