Volcanic Eruptions

Volcanic Eruptions
Think about the force released when the
first atomic bomb exploded during WWII.
Now imagine an explosion 10,000 times
stronger, and you will get an idea of how
powerful a volcanic eruption can be!
Volcanoes are areas of the Earth’s surface
through which magma and volcanic gases
Volcanoes erupt both explosively
and non-explosively
Non-explosive eruptions are most common:
• Calm flows of lava
• Can release huge amounts of lava
• Much of the sea floor and NW region of
the US are covered with lava from nonexplosive eruptions.
Volcanoes erupt both explosively
and non-explosively
Explosive eruptions are much rarer:
• Can be incredibly destructive
• Clouds of hot debris, ash, and gas rapidly shoot
out of the volcano
• Ash-molten rock blown into tiny particles that
harden in the air (may circle in the atmosphere
for years
• Larger pieces of debris fall closer to the volcano
• Can demolish a mountainside in seconds
Magma that has a high level of water, CO2,
or silica tends to erupt explosively
The composition of magma affects how explosive
a volcanic eruption is:
• The higher the water content, the more
explosive the eruption
• Lava releases pressure (CO2- as it moves to the
surface-just like shaking up a soda can)
• Silica rich magma is very stiff and hardens easily
plugging vents, results in explosive eruptions
when the pressure builds up
Lava can be classified by its viscosity and by
the surface texture of lava flows
• Lava is liquid magma that flows from a
volcanic vent, its viscosity can vary (thick,
like a milkshake or thin, like milk)
• High viscosity=stiff; low viscosity=fluid
• Blocky lava and pahoehoe (puh HOY hoy) have
high viscosity and flow slowly
• Aa (Ah Ah) and pillow lava have low viscosity
and flow quickly
Pyroclastic material, such as ash and
volcanic bombs, forms when magma
solidifies as it travels through the air
Pyroclastic material forms when magma is blasted into the
air and hardens or when powerful eruptions shatter
existing rock.
• Size can vary from tiny particles suspended in the
atmosphere to boulders the size of houses
• Volcanic bombs -large blobs of magma that harden in
the air
• Lapilli (little stones)-pebble size pieces of magma that
harden before they hit the ground
• Volcanic blocks -largest, solid pieces erupted from a
• Volcanic ash -tiny, glass-like slivers of hardened magma
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