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VOLCANOES
YEAR 7
3. VOLCANIC ACTIVITY
• Lava begins as magma, formed in the
asthenosphere. It rises toward the surface,
into any cracks in the rock above. The gases
form bubbles. When an opening develops in
weak rock on the surface, a volcano erupts.
• When a volcano erupts, the force of
expanding gases pushes magma from the
chamber through the pipe until it flows or
explodes out of the vent.
• Inside a volcano:
– Magma chamber: magma is collected there
– Pipe: long tube in the ground that connects
the magma chamber to Earth's surface.
– Vent: opening where molten rock and gas
leave the volcano.
– Lava flow: area covered by lava as it pours
out of a vent
– Crater: bowl-shaped area that may form at
the top a volcano around the volcano's
central vent.
Pipe
Magma Chamber
• The force a volcanic eruption depends on
different things related to the magma:
– Amount of gas dissolved
– Temperature
– Silica content (Silicon plus Oxygen)
• Type of volcanic eruptions:
– Quiet eruptions
• Magma low in silica, low viscosity and flow
easily. I.e.: Hawaii volcanoes
– Explosive eruptions
• Magma high in silica, high viscosity, making it
thick and sticky. I.e.: Mount St. Helens
• Explosive eruption breaks the lava into
fragments that quickly cool and harden into
pieces of different sizes: ash (small pieces) and
bombs (large pieces)
• Pyroclastic flow occurs when an explosive
eruption hurls out ash, bombs, gases…
QUIET ERUPTION (KILAUEA)
EXPLOSIVE ERUPTION (MT ST.HELENS)
PYROCLASTIC FLOW
BOMB
• VOLCANO HAZARDS
– Both type of eruptions can cause damage far from
the crater’s rim
– Quiet eruption:
• Lava flows from vents, setting fire to and then burying
everything in its path. It can cover large areas with a
thick layer of lava
– Explosive eruption:
• Volcano can belch out hot clouds of deadly gases, ashes,
bombs…
• Volcanic ashes can bury entire towns. If it becomes wet,
the heavy ash can cause roofs to collapse.
• If a jet plane sucks ash into its engine, the engine may
stall.
• Eruptions can cause landslides and avalanches of mud,
melted snow and rock
• Geologist have been more successful in
predicting volcanic eruptions than earthquakes.
• Geologist monitor volcanoes checking different
parameters and small earthquakes around it,
caused by the movement of magma:
– Surface changes in elevation (magma moving
underground)
– Gases (escaping from the volcano)
– Temperature increase in the underground
water (magma is nearing the surface)
• Stages of a volcano (From less than a
decade to more than 10 million years):
–Active or live: it is erupting or has
shown signs that it may erupt in the
near future.
–Dormant or sleeping: scientist expect
to awaken in the future and become
active.
–Extinct or dead: it is unlikely to erupt
again