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Section 6.1• Vocabulary to know: • Volcano
• Quiet eruptions• Explosive eruptions• Crater• Central vent• Dike• Lava• Pipe • Magma chamber• Magma• Aa• Pahoehoe• Pillow lava• Blocky lava• Pyroclastic• Volcanic bombs• Lapilli• Volcanic ash• Volcanic blocks
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What is a Volcano?
• Volcano- – a
mountain that forms when magma (As well as volcanic gases) reaches the surface
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How do volcanoes form?Magma reaches the surface through a vent
Explosive eruption. Boiling mud and ash are hurled into the air
Hot lava then flows out through the vent. The lava cools and hardens
The process keeps on repeating itself making the volcano grow larger
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Types of Eruptions• Quiet (Non explosive)
eruptions- – Have very hot, low
silica, low viscosity magma
• Explosive eruptions- – High amounts of water– High silica, and high
viscosity magma• Clogs a volcanic pipe…• Enormous pressure
builds up…• Steam gets trapped…• Volcano explodes!!!
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Non explosive volcanic eruptions• 4 different types of lava:
Aa- forms brittle crust…crust gets torn into little pieces as lava flows underneath
Pahoehoe- flows very slowly…like wax dripping from a candle
Pillow lava- forms when eruptions occur underwater
Blocky lava- cool and stiff. Doesn’t travel far from the erupting vent of the volcano
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Volcano Structure1. Crater-
• bowl shaped pit at top of central vent
2. Central vent- • magma escapes to the
surface3. Dike-
• leads to side vent
4. Lava- • magma that has reached the
surface
5. Pipe- • narrow vertical channel
6. Magma chamber- • pocket where magma
collects
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Explosive volcanic eruptions• Produce pyroclastic material-
– Forms when magma explodes from a volcano and solidifies in the air
– 4 types:
Volcanic bombs-
•Large blobs of magma that harden in the air
Lapilli-
•Pebble-like bits of magma that harden before they hit the ground
Volcanic ash-
•Majority of pyroclastic material
Volcanic blocks-
•Solid pieces of rock erupted from volcano
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What are pyroclastic flows?• Pyroclastic flow-
– Very dangerous– produced when
enormous amounts of hot ash, dust, and gases are ejected from volcano
– can race downhill at speeds of more than 200 km/h
– temperature at the center can exceed 700°C
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Section 6.2
• Vocabulary to know: • Shield volcano• Cinder cone volcano• Composite volcano
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Shapes of Volcanoes• Shield
volcano:– Broad– Gently
sloping
• Eruptions:– Hot, flowing
basaltic lava.– Travels a
long way before it solidifies
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Mount Kilauea (Shield Volcano)
• Located in Hawaii• Presently the most active
volcano on the planet• Can be walked up to
because of its non-violent explosions
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Shapes of Volcanoes• Cinder cone
volcano:– Small– Steep sides
• Form from:– Ash and
cinders that are ejected into the air and fall back onto the volcano
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Shapes of Volcanoes• Composite
volcano:– Tall– Steep sides
• Built up from viscous lava, ash, and volcanic bombs
• Eruptions:– High silica– High viscosity
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Mount St. Helens
• Composite volcano• Erupted on May 18,
1980• Killed over 55 people• Blast removed 1000 ft off
the top of the volcano• The explosion could be
heard as far away as Canada
• Notice the trees…
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Krakatau
• Composite volcano• Erupted on August 26, 1883
in Indonesia• Explosions were heard 2200
miles away in Australia• Ash was propelled 50 miles
into the air– This ash blocked the sunlight
for 2 ½ days
• Created a tsunami 120 feet tall
• Killed 36,000 people
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Mount Vesuvius
• Composite volcano• Erupted in Pompeii in 79
AD• 10 feet of ash piled on
top of the buildings after the explosion
• Considered to be one of the most dangerous volcanoes in the world– 3,000,000 people live
close to it
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Mount Pinatubo• Erupted in 1991• A 7.7 Richter scale
earthquake caused the volcanic eruption
• Scientists predicted the eruption, and the residents were evacuated
• Caused the entire world’s temperatures to drop by 1 degree
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Section 6.3
• Vocabulary to know • Plate boundary• Ring of fire• Divergent boundary• Convergent boundary• Hot spot
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Most Volcanoes Occur at Plate Boundaries
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Ring of Fire• Mostly
found along the edge of the Pacific plate
• Contains nearly 75% of the worlds active volcanoes found on land
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Divergent Boundary• Magma
escapes to the surface as the plates move apart– Magma rises
to fill the gap between the two separating plates
– Mid ocean Ridge
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Convergent Boundary• Oceanic plate is
subducted into the mantle…
• This causes melting…
• Magma forms and rises to the surface…
• Volcano created!!!• Why does the
magma rise?– It’s less dense
than the rocks around it.
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Hot Spot• Hot spot stays
in one place…• Plates move
over the top of it…
• Over time, a chain of volcanoes is formed!!!
• Is Kauai an active volcano?
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Iceland• Above sea level
because there is a hot spot that works with the mid ocean ridge
• What rocks would be the oldest?
• What would happen to a house built on the mid ocean ridge?