Transcript volcano

Volcanoes
Exploding
mountains?
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VOLCANOES
The word "volcano" comes from the little island of
Vulcano in the Mediterranean Sea off Sicily (Italy).
Centuries ago, the people living in this area believed
that Vulcano was the chimney of the god Vulcan ( he
was the blacksmith of the Roman gods -- he made
things out of metals).
They thought that the hot lava pieces and clouds of
dust erupting from Vulcano came from Vulcan's
furnace as he made thunderbolts for Jupiter, king of
the gods, and weapons for Mars, the god of war.
In Polynesia the people attributed eruptive activity to
the beautiful but wrathful Pele, Goddess of Volcanoes,
whenever she was angry or spiteful.
Today we know that volcanic eruptions are not supernatural but can be studied and interpreted by
scientists.
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So, What is a volcano?
Volcanoes are mountains, but they are very
different from other mountains; volcanoes are
built by the accumulation of their own eruptive
products -- lava, bombs (hardened lava blobs),
ashflows, and tephra (airborne ash and dust).
A volcano is most commonly a cone shaped hill
or mountain built around a vent that connects
with pockets of molten rock (magma) below the
surface of the Earth.
The term volcano also refers to the opening or
vent through which the molten rock and
associated gases are expelled.
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As you heard last week…
Volcanoes generally form along plate margins
Either where the plates are approaching each
other and one is sliding under the other –
destructive margins
Or where they are moving away from each
other – constructive margins
There are a few exceptions – called hot spots –
where the magma bursts through a particularly
thin bit of oceanic crust, for example in Hawii.
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Distribution of some of the
Ring of Fire world’s major volcanoes
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How do they form?
This one is forming on a destructive plate
As the oceanic crust
slips beneath the
continental plate,
some of the magma
gets trapped above.
This is force out
through any crack it
can find in the
continental plate.
Violà – you have a
volcano!
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Which of these are volcanoes?
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Types of volcano
They all were !
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Shield Volcanoes
Broad, slightly
domed-shaped
Made of layers of
frozen lava
May be 100s of km
across and have a
large crater
Produced by mild
eruptions of large
volumes of lava
Non-explosive eruptions
Mauna Loa on Hawaii is a
good example
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Cinder Cone Volcanoes
Made of loose grainy
cinders and no lava
Steep slope angle
Rather small size about
1 km across with a small
crater
Frequently occur in
groups
Moderately
explosive
Example: Paricutin
(Mexico)
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Composite Volcanoes
Most are located adjacent
to the Pacific Ocean (e.g.,
Fujiyama, Mt. St.
Helens)
Large, classic-shaped
volcano (1000’s of ft. high
& several miles wide at
base) with a small crater
Composed of layers of lava
flows with layer of cinder
and ash in between
May have very explosive
eruptions
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A composite volcano
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Comparing sizes
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Which type is this?
A: Mount Rainier, Washington State in
western USA
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Which type is this?
B: Paricutin, Mexico
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Which type is this?
C : Mauna Loa, Hawaii
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Which type is this?
D: Papua New Guinea
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Which type is this?
E: Popocatepetl, Mexico
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How did you do?
A = composite (Mount Rainier, WA)
B = cinder cone (Paricutin, Mexico)
C = shield (Mauna Loa, Hawaii)
D = cinder cone (Papua New Guinea)
E = composite (Popocatepetl, Mexico)
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Types of Lava
Volcanic eruptions may be quiet outflows of
lava which are so peaceful that one can stand
close enough to toss in pebbles or so
explosively violent that they blow mountains
apart and blast everything within a hundred
miles to smithereens (not recommended for
close observation).
Both the shapes of volcanoes and the violence
of volcanic eruptions depend on the same
rather mundane thing: the physical properties
of erupting lavas.
The two most important properties of lava are
– its viscosity (its stickiness), and
– the amount of gases dissolved in the liquid rock.
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Viscosity
Is a term that describes the fluidity or
"runniness" of the lava.
Some lavas are very "runny," not quite like
water, but more like warm honey or hot wax.
When these lavas erupt, they flow for large
distances before cooling enough to turn solid.
You can imagine what kind of volcanic mountain
you could make with runny lavas by thinking
about (or carefully doing) pouring hot wax on a
large sheet of paper.
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Viscosity
The wax spreads out into a large, flat layer.
Let it cool and harden and then pour another
layer. The second "flow" of wax will partly
pond on the first and partly run off onto the
paper to form another flat layer.
If you keep pouring more and more "flows," you
will get a large, but almost flat pile of wax.
Therefore, many small eruptions of runny lavas
form large, almost flat mountains like shield
volcanoes.
Eruptions of huge amounts of really runny lavas
form flood basalt type volcanoes.
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Viscosity
Other lavas are very "pasty" like soft
clay and hardly flow at all. Imagine piling
lumps of soft ice cream on a big, flat
dish--you would end up with a tall, narrow
pile. Likewise, pasty lavas form tall,
steep-sided mountains like composite
volcanoes.
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Why is some lava sticky and some
not?
The viscosity of lava depends on several
things.
The amount of silica . More than 80% and it is
VERY sticky. Get as low as 50% and it is quite
runny
The amount of dissolved gas in it. If there is
a lot of gas in a runny lava, you might get a
fountain of cinder flying out
But if you have a lot gas in sticky larva then
you get enormous and very dangerous
explosions
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Two types of lava
Pahoehoe and Aa
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Other volcanic landforms
Calderas
• Steep-walled depressions at the summit
• Size generally exceeds 1 km in diameter
Example Santorini in Greece
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Caldera
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Volcanoes and climate
Explosive eruptions emit huge quantities
of gases and fine-grained debris into the
atmosphere which filter out and reflect
a portion of the incoming solar radiation
Examples of volcanoes affecting climate
Mount Tambora, Indonesia – 1815
Krakatau, Indonesia – 1883
Mount Pinatubo, Philippines - 1991
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VOLCANIC ACTIVITY
ACTIVE - A volcano that has erupted in the
recent past and is expected to erupt again.
Any names?
DORMANT - A “sleeping” volcano. A volcano
that has not erupted in the recent past, but
could erupt again. One in Yellowstone has not
erupted fro 640,000 years BUT there are still
earthquakes and steam emissions so it could!
EXTINCT - A volcano that is not expected to
erupt again. This is because there is no longer
a source of magma. Castle rock in Edinburgh is
an example
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Homework
Choose an active volcano (or at least one
that has erupted in the last 20 years or
so)
Find out its name and where it is – I will
send you a world map to move a X to the
right spot.
Find out which sort of volcano it is –
shield, composite or cinder cone
Find out 4 other things about it
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Suggestions for your other 4
things
A picture of your volcano
Geographic setting:
– Is it on an island or in a mountain range?
– Is it near towns or cities or is it isolated
When did your volcano last erupt?
– what do you know about it?
– Was the eruption hazardous to people? What happened?
If the volcano erupts again, what are the possible
hazards? Does it pose a threat now?
What are 2 cool facts about your volcano?
What is a question you still have about your volcano?
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