Download Violent Volcanoes

Violent Volcanoes
- Kaboom!
What did Mummy Volcano say to
Baby Volcano?
- I lava you!
Volcanoes (origins…)
So, who on Earth came up with the name volcano to describe a
smouldering mountain that can explode? Well, there are different
stories around the world to explain what causes volcanoes, but you
can blame the actual name on the ancient Romans and their hottempered fire god, Vulcan…
According to legend, Vulcan lived on the island of Vulcano, inside a
smouldering mountain.
Volcanoes (origins…)
All the smouldering, sparks and rumbling noises were caused by
Vulcan’s frantic activities. He was blacksmith to the gods… He made
weapons for Mars…
Armour for Hercules…
Volcanoes (origins…)
And thunderbolts and lightning for Jupiter.
But Vulcan used his skills in other
ways too. For no good reason,
Vulcan would pick on villagers and
terrorise them with fire, lightning,
lava flows and explosions!
So, which came first, Vulcan or Vulcano? No one knows, but the
name, tweaked a bit, stuck.
Volcanology (a proper definition)
• Includes all processes by which solid, liquid or
gaseous materials are forced into the Earth’s
crust or are ejected onto the surface
Lesson Objectives
• Main features of a volcano
– Physical characteristics
– Internal forces
• Processes that create volcanoes
• Life of volcanoes
Main Features of a Volcano –
Physical Characteristics
• Vent: An opening in the
Earth’s surface
• Pipe: A channel which
allows the magma to rise
to the top of the volcano
during an eruption
• Crater: A bowled-shaped
opening at the top of the
volcano
• Cone: The shape of the
volcano
Main Features of a Volcano –
Internal Forces
• When the temperature beneath the Earth’s surface is so
great, magma (molten mantle) is formed
• Magma that reaches the Earth’s surface is called lava
• Vulcanicity is the process in which magma and other
materials reach the Earth’s surface
Main Features of a Volcano –
Internal Forces
• Volcanoes grow by intrusion and extrusion
- An intrusion is magma that moves up into a volcano and then it stops,
never erupting  volcano grows on the inside
- An extrusion is an eruption  can add layers of lava or ash  volcano
grows on the outside
 The outpouring of the lava onto the Earth’s surface is called an eruption.
• Hardened lava from eruptions through a single hole or vent
may result in a cone-shaped mountain called a volcano
Processes that Create Volcanoes
• Convergent plates
– Mantle above subducting plate,
below over-riding plate hot but
not hot enough to melt rock
– Oceanic plate on the ocean
floor for tens of millions of
years, incorporating a lot of
water and buried in sediment
– As plate subducts, comes into
contact with overlying hot
mantle
– Causes water and sediment to
melt and move into overlying
mantle
– Lowers melting temperature of
mantle enough to generate
magma
• Divergent plates
– Accumulation of lava at the
surface
– Magma mostly originates by
melting in the mantle
– As hot rock gets closer to the
surface the pressure
decreases and the rock begins
to melt  magma.
– Magma more buoyant than
the surrounding rock  rises
towards surface and may
supply a volcano (or solidify
before it reaches the surface)
Processes that Create
Volcanoes
• Hotspots
– Source of heat and/or magma
supplied to surface
– BUT exact nature of hotspots
poorly known
– Stationary with respect to the
moving lithosphere
– Linear chains of volcanoes form
on the overlying plates
– Volcanoes get older as you look
in the direction of plate motion
Example of Volcanic Hotspots:
The Hawaiian Islands
Example of Volcanic Hotspots:
The Hawaiian Islands
• This movement takes it to the northwest compared to the layers
below it at a rate of 5 to 10 cm/yr
• As the plate moves over a fixed spot deeper in the Earth where
magma (molten lava) forms, a new volcano can punch through this
plate and create an island
• As the plate moves away, the volcano stops erupting and a new one
is formed in its place
• With time, the volcanoes keep drifting westward and getting older
relative to the one active volcano that is over the hot spot
• As they age, the crust upon which they sit cools and subsides +
erosion of the islands once active volcanism stops  shrinking of
the islands with age  eventual submergence below the ocean
surface
Life of Volcanoes
• Active
• Dormant
• Extinct
Life of Volcanoes
• Active
– A volcano that has shown eruptive activity within
recorded history
– Need not be in eruption to be considered active
– 600 volcanoes on Earth considered to be active
– 50 to 60 of volcanoes actually erupt yearly
Life of Volcanoes
• Extinct
– A volcano that has not shown any historic activity
– Usually deeply eroded, and shows no signs of recent
activity
– How old a volcano must be to be considered extinct
depends to a large degree on past activity.
• Yellowstone Caldera: about 600,000 years old and is deeply
eroded, but geothermal activity, hot springs, and geysers all
point to the fact that magma still exists beneath the surface
 not considered extinct
• Other volcanoes that are deeply eroded, smaller, and much
younger than Yellowstone, that show no hydrothermal
activity may be considered extinct
Life of Volcanoes
• Dormant (aka sleeping volcano)
– Somewhere between active and extinct
– Has not shown eruptive activity within recorded history but
shows geologic evidence of activity within the geologic recent
past
– Because the lifetime of a volcano may be on the order of a
million years, dormant volcanoes can become active volcanoes
all of sudden  perhaps the most dangerous
– Examples:
• Yellowstone Caldera would be considered a dormant volcano.
• Mount St. Helens was a considered a dormant volcano, having not
erupted for 123 years, before its reawakening in 1980.
• Mount Pinatubo in the Philippines had been dormant for over 400
years before its eruption in 1991.
• Mount Vesuvius, near Naples, Italy was considered an extinct
volcano prior to its devastating eruption of 79 A.D.
Life of Volcanoes
• Dormant (aka sleeping volcano)
– Examples:
• Yellowstone Caldera would be considered a dormant volcano.
• Mount St. Helens was a considered a dormant volcano, having not
erupted for 123 years, before its reawakening in 1980.
• Mount Pinatubo in the Philippines had been dormant for over 400
years before its eruption in 1991.
• Mount Vesuvius, near Naples, Italy was considered an extinct
volcano prior to its devastating eruption of 79 A.D.