Volcanic Eruptions
• Hawaii – many myths about Pele, the fire goddess
of volcanoes
• Pele lives in the depths of Hawaii’s erupting
volcanoes
• When Pele is angry, she causes a volcanic
eruption
• Pele’s hair type of volcanic rock
• As lava stretches and hardens
into thin strands
Magma Reaches Earth’s Surface
• Inside a volcano
• Magma chamber – beneath a volcano, magma
collects in a pocket
• Magma moves upward through a pipe
• Molten rock and gas leave the volcano
through an opening called vent, at the top of
the volcano
• Vents can form on the side of the volcano
• Lava flow an area covered by lava as it pours
out of a vent
• Crater is a bowl-shaped area that may form at
the top of the volcano around the central vent
A Volcanic Eruption
• The carbon dioxide in the magma expands and
forms bubbles, which rush to the surface,
these dissolved gases are under pressure
• When a volcano erupts, the force of the
expanding gases pushes magma from the
magma chamber through the pipe until it
flows or explodes out the vent.
Kinds of Volcanic Eruptions
• Quiet Eruptions – low in silica
• Low silica – magma has low viscosity and
flows easily
• Lava flows easily from the vent, and flows for
many kilometers, can produce both pahoehoe
and aa
• Explosive Eruptions – magma high in silica, high
viscosity magma is thick and sticky
• High viscosity magma builds up in the volcano’s
pipe, gases build up pressure until they explode.
• Pebble-size particles are called cinders
• Large pieces are called bombs (baseball to car size)
• Pyroclastic flow occurs when an explosive eruption
hurls out a mixture of hot gasses, ash, cinders , and
bombs
• Obsidian forms when lava cools very quickly,
giving it a smooth, glossy surface like glass
• Pumice forms when gas bubbles are trapped
in fast cooling lava, leaving spaces in the rock
• Volcano Hazards
• Quiet Eruption, lava flows setting fire and
burying anything in its path, can cover large
areas with thick layers of lava
• Explosive Eruptions puts out hot clouds of
deadly gases, ash, cinder, and bombs.
• Ash can bury entire towns
• If ash becomes wet, becomes heavy and
collapse roofs
• Planes can suck in ash and make the engines
stall
• Cause landslides, avalanches of mud, melt
snow and rock
Stages of Volcanic Activity
• Volcanoes can last from less than a decade to more
than 10 million years
• Active, (alive) volcano is one that is erupting or has
shown signs that it may erupt in the near future
• Dormant volcano may awaken in the future and
become active
• Extinct (dead) unlikely to erupt again