Volcanoes Volcano mountain that forms in Earths crust when molten material magma reaches the surface Remember magma is molten rock below ground lava is molten rock at the surface ID: 790376
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Slide1
Chapter 5: Volcanoes
5.1 Volcanoes and Plate Tectonics
Slide2Volcanoes
Volcano:
mountain that forms in Earth’s crust when molten material (magma) reaches the surface.
Remember,
magma
is molten rock below ground;
lava
is molten rock at the surface.
Slide3Volcanoes
Volcanoes form along plate boundaries.
At divergent boundaries, the crust cracks and allows molten rock to rise (mid-ocean ridge).
At convergent boundaries, one plate can sink beneath the other, which helps bring magma to the surface (on ocean floor).
Slide4Island Arc
An
island arc
is a string of islands formed from volcanoes.
Some common ones are Japan, New Zealand, the Aleutians, and the Caribbean islands.
Some continental volcanoes include Mount St. Helens and Mount Rainier.
Slide5Hot Spots
Some volcanoes form from
hot spots
: an area where material from the mantle rises through the crust.
Hot spots are stationary beneath the crust, and the plates move over them.
Slide6Chapter 5: Volcanoes
5.2 Volcanic Eruptions
Slide7Volcanic Structure
Magma chamber:
pocket of magma beneath the volcano.
Pipe:
connects the magma chamber to Earth’s surface.
Vent:
the area where molten rock and has leave the volcano.
Lava flow:
the spread of lava as it leaves the vent
Crater:
bowl-shaped area around the central vent.
Slide8Volcanic Structure
Slide9Volcanic Eruption
Dissolved gases are built up in magma.
As they expand, pressure increases, and eventually forces the magma through the pipe and out of the vent.
Slide10Volcanic Eruption
Eruptions can be quiet or explosive; it depends on the magma’s silica content and the thickness of the magma.
Slide11Volcanic Eruptions
If magma is very hot and low in silica, the volcano erupts quietly.
Lava can flow for long periods of time; built the Hawaiian islands.
Magma that is high in silica explodes from a volcano.
Mount St. Helens in Washington erupts this way.
Slide12Rock Fragments
Volcanic Ash
: Consists of particles ranging from the size of dust to the size of rice grains
Volcanic Cinders
Volcanic Bombs
Volcanic Blocks
: Solid pieces of rock, as big as houses
Slide13Volcano Hazards
Quiet eruptions have large lava flows and burn and bury almost everything in its path.
Explosive eruptions release dangerous materials that form clouds around the volcano.
Pyroclastic flow:
mixture of hot gases, ash, cinders, and bombs that rush down a volcano.
Slide14Volcano Activity
An
active volcano
is one currently erupting or showing signs of erupting soon.
A
dormant volcano
is one that is “sleeping” but expected to turn active in the future.
An
extinct volcano
is one that is unlikely to ever erupt again.
Slide15Predicting Activity
Geologists use
tiltmeters
to measure small changes in the ground caused by magma movement.
They also monitor earthquakes, which can cause volcanic eruptions.
They measure gas from the volcano, and also keep track of temperatures.
Slide16Chapter 5: Volcanoes
5.3 Volcani
c Landforms
Slide17Calderas
A
caldera
is a hole left behind when a volcano collapses.
Lakes may form in this hole over time.
Usually associated with shield and composite volcanoes.
Slide18Cinder Cone Volcanoes
A steep, cone-shaped hill or small mountain
Formed by ash, cinders, and bombs building up around the volcano’s vent.
Usually magma high in silica
Slide19Composite Volcanoes
Tall, cone-shaped mountains with layers of lava and ash
Usually alternates between quiet and explosive
Slide20Shield Volcanoes
Wide, gently sloping mountain
Thin layers of lava pour out of a vent and cool in layers.
Hot spot volcanoes are usually this type.
Slide21The largest volcano on Earth, Mauna Loa.
Slide22Lava Plateaus
Lava plateaus are made from thin, runny lava floods that cool and solidify.
Slide23Magma Landforms
Volcanic neck:
forms when magma hardens in a volcano’s pipe and the rock wears away.
Slide24Magma Landforms
Dike:
magma that moves across rock layers
Sill:
magma that squeezes between rock layers
Slide25Magma Landforms
Batholith:
mass of rock formed when a large body of magma cools inside the crust.
Slide26Magma Landforms
Dome Mountains:
bodies of hardened magma that are pushed upward toward the surface.