Volcano
- Vent, opening in the surface of earth - - Magma, gases, and ash erupt.
- Occurs mainly near plate tectonic plates/boundaries. – Convergent and Divergent
- Common around Pacific basin…..Called “Ring of Fire”
- Word refers to form or structure (usually conical)….produced by accumulations of
erupted material.
Volcano Formation and Eruptions
- May be violent
- Possible catastrophic or tragic
- May be mild
- Explosive eruptions are blasts of steam, ash, lava, etc….creates spectacular displays
- Quieter eruptions….molten rock pushes thru long cracks in the earth’s crust and floods
surrounding landscape.
- Creates thick lava plateaus
- Magma is name of molten rock when in the earth…called lava when outside of earth.
- 80% of magma is composed of basalt rock
- Magma rises because: less dense than rocks at lower depths, heat weakens surrounding
rock, and expanding gases within molten rock.
- Volcanic Material moves toward the surface thru “channel ways” or volcanic conduits
(pipe) and extruded thru vents at the surface of earth.
- Products of Volcano is classified in 2 groups…
Lava – fluid phase of volcanic activity
Pyroclastics or tephra – various size of particles of hot debris thrown by volcano
- Gas may be poisonous
- Explosive Eruptions may bring earthquakes, high columns
- of vapors, lightning, and strong whirlwinds.
- Most volcanoes occur along divergent plate boundaries, such as the mid-ocean ridge, or
in subduction zones around the edges of the oceans.
Types of Volcanoes:
- Classified by shape and size
- Determined by volume and type of volcanic material ejected
- Sequence and variety of eruptions
3 Most Common Types of Volcanoes:
Shield – low, broad profile
-Lava spreads over wide areas
- No build up of cone or not much
-Ex: Hawaii composed of Shield Volcanoes..built up layers or plateaus
Strato or Composite Volcano – Most common form
- Cone constructed
- Composed of both lava and pyroclastic material.
- Explosive and Violent Eruptions
Cinder Cone Volcano – Conical Hill
- Mostly cinder size pyroclastics
- Explosive
- Steep slopes above surrounding area
Volcanic activity typically alternates between short active periods and much longer dormant
periods.
-
Extinct Volcano – not erupting, not likely to erupt in the future
Dormant Volcano – while currently inactive, has erupted in history
And is likely to erupt again in the future.
Active Volcano – “Self Explanatory”  “live” a volcano is erupting or shows signs that
it may erupt in the near future.
Late Stages of Volcanic Activity:
- Magma can heat circulating groundwater which produces “hot springs” and “geysers.”
- Geysers – hot water fountain with great force. Ex: Old Faithful in Yellowstone
800 Volcanoes active today
75% are located Pacific Ring of Fire
Vocabulary
Volcano – weak spot in the crust where molten material, or magma comes to the surface.
Magma – molten mixture of rock-forming substances, gases and water from the mantle.
Lava – magma when it reaches the surface.
Ring of Fire – a volcanic belt located in the Pacific Ocean.
Island Arc – a string of islands created by volcanoes
Hot Spot – is an area where magma from deep within the mantle melts through the crust like a
blow torch.
Magma Chamber – a pocket, beneath a volcano, where magma collects.
Pipe – a long tube in the ground that connects the magma chamber to the Earth’s surface.
Vent – the location or opening where molten rock and gas leave the volcano.
Lava Flow – is the area covered by lava as it pours out of a vent.
Crater – is a bowl-shaped area that may form at the top of a volcano around the volcano’s central
vent.
aa – Lava that is cooler and slow moving.
Pahoehoe – fast moving, hot lava.
Note: the more silca (material from the Earth’s crust and mantle)
the thicker the lava becomes.
Pyroclastic Flow – occurs when an explosive eruption hurls out ash, cinders, and bombs as well
as gases.
Bomb – chunks of rocks and debris released into the air from an eruption.
Hot Spring – forms when groundwater heated by nearby body of magma rises to the surface and
collects in a natural pool.
Geothermal Energy – clean, reliable energy provided by a volcano (magma).
Caldera – The huge hole left by a collapse of a volcanic mountain.
Lava Plateau – High level area of lava.
Dike – when magma forces itself across rock layers and hardens.
Sill – when magma squeezes between layers of rock.
Batholith – is a mass of rock formed when a large body of magma cools in the crust.
Geyser – a fountain of water and steam that builds up pressure underground and erupts at regular
intervals.
Viscosity – Tendency to resist flow. It’s a property of liquids.