Volcanoes
Get Ready for an
ERUPTION!!!
What is a volcano?
• A weak spot in the crust where
molten material, or magma, comes
to the surface
• Magma- melted rocks and minerals
from the mantle
• Lava- Magma that reaches the
surface
Where are volcanoes located?
• Volcanoes can be found:
– Diverging Plate boundaries (mid-ocean
ridge)
– Converging plates with subduction zones
• Oceanic plate vs. oceanic plate
• Oceanic plate vs. continental plate
– Hot spots
• Area where magma from deep within the mantle
melts through the crust like a blow torch
– Example: Hawaiian Islands
What is the Ring of Fire?
• The majority of Volcanoes on earth are
located around the edge of the Pacific Plate,
which is the tectonic plate that holds the
Pacific ocean.
• The outer boundary of this plate is nicknamed
the Ring of Fire because of the number of
Earthquakes and Volcanoes that occur there.
Results of Volcanoes
• Are constructive:
– add new rock to existing land
– form new islands
• Can be destructive
– explosive eruptions changes the
landscape of and around the volcano
Eruptions
• Why do volcanoes erupt?
– Less dense magma seeps upward through
cracks and creates volcanoes
– Gas in the magma is trapped and builds
pressure
– Closer it gets to surface the less
pressure it has and the gases separate
(bubbles)
– Gases dissolve on the surface and magma
is carried out
Types of Eruptions
• determined by amount of silica (material
made from the elements oxygen and silicon)
• 2 types:
– Quiet
• Lava moves steadily and easily
– Explosive
• Thick, sticky lava plugs vent like a cork and
builds up pressure
• Explodes and releases pyroclastic flow
– Volcanic ash: fine, rock particles
– Cinders: pebble sized particles
– Bombs: baseball to car sized particles
Types of Rocks Produced
• Type of lava produces different
types of rocks
– High silica lava: thicker, sticky,
lighter colored
• Rhyolite
• Pumice
• obsidian
– Low silica lava: flows readily, dark
colored
• basalt
Stages of a Volcano
• Active: (live) erupting or has shown
signs that it may erupt In the near
future
• Dormant: (Sleeping) is not currently
erupting but may/can erupt in the
future
• Extinct: (dead) unlikely to erupt again
Other Volcanic Activity
• Hot springs
– Groundwater is
heated by near
by magma
rising to the
surface and
collects in
natural pools
Other Volcanic Activity
• Geyser
– Rising hot water
and steam that
gets trapped
underground and
builds pressure
until it sprays to
the surface
Land Formations from Lava & Ash
• Shield Volcano
– Created by hot spots
– Gently sloping
• Cinder Volcano
– Steep
– Cone-shaped hill/mountain
• Composite Volcano
– Tall, cone-shaped mountain
– Alternating layers of ash and lava
Land Formations from Lava & Ash
• Lava Plateaus
– Lava moves far from the volcano before
cooling which forms high plateaus
• Calderas
– Huge hole left by the collapse of a volcanic
mountain
• All magma has been emptied leaving a hollow
shell that collapses