An ancient
Volcano erupts.. and you can hear the explosion,
you can see the fire rise into a
fountain…. enflaming the sky...
you can smell the gases, feel
the ground tremble,
taste the ash
in your mouth, your eyes burn... you feel the heat… and your
senses become aware of
the planet… and you stand in awe.
Magnificent and Powerful... Volcanoes are the
bringers of Life and death. With the risk comes the beauty of the
Voluptuous
Volcano
lands, where the mountains
and valleys are the lushest
green
and the
land is so fertile, which creates the most
fantastic diversity of Life in all areas and
creates the cloud and rainforests.
The skies are more beautiful... in the Voluptuous
Volcano Lands... and more mysterious.
Volcanoes are fascinating... they bring you information about the interior of the planet, down to
60
miles or more
and help you study
the evolution
of the
planets, on a human time scale. In
geology,
you think of
processes taking thousands or even
millions of years.
All volcanoes are born... when hot magma
rises to
the surface,
and infiltrates
a weak spot...
in the Earth's outer crust, and finally breaks through.
 Most of the
600 or more, active volcanoes on Earth... are
associated with the boundaries of the
tectonic plates,
which
are the seven great
plates, that carry the oceans
and continents.
They are especially common in subduction zones,
which occur when one plate dips beneath another.
As the plate dives into the mantle... the layer
of hot,
flexible rock,
on which the plates glide...
is gradually heated.
That in turn,
releases fluids which heat the
overlying rock,
producing blobs of
molten rock...
that rise to the surface.
The molten rock or magma, collects in weak
patches of crust, in structures called magma
chambers. If the pressure in the magma chamber
builds high enough, the magma will erupt.
 
A Volcano is Born
The lithosphere is made up of the crust and the upper most layer
of the
mantle, and is divided up into 16
major plates. As the
plates of the lithosphere shift, they disrupt portions and pockets
of
the mantle
below it. This disruption causes steam and gasses
within
the mantle then
into liquid magna, these pockets of
liquid magma... are called "hot spots". The
liquid magma then makes its
way up through the lithosphere and erupts
onto the earth as lava.
What are Plate Tectonics?
"Plate" depicts the plates of the lithosphere of
earth.
"Tectonics"
is the
study of geological features.
Therefore,
"plate tectonics" is
the study of
the shifting of the lithosphere
plates... which cause
the
eruption of volcanoes and are the
advent
of earthquakes.
Plates can shift towards each other, away from
each other,
or they can
shift side by side. The way
in which these plates
move in relation
to each
other... cause the different types
of physical
conditions...
that create volcanoes and earthquakes.
Volcanic eruptions
begin when magma comes
to the surface...
through hot spots, spreading
centers or subduction zones. The Tectonic
plates are part of the
Earth's surface
that is constantly
spreading apart in
slow motion.
The Tectonic plates pull
apart, and magma
fills the
spaces.
This pulling apart of the spreading plates... is called
an oceanic spreading center. The Mid-Ocean ridge (46,600 miles
long), was created
by a spreading center. When you press them together,
you've created
a subduction
zone. Subduction zones are created
with the lighter
continents. This type of movement
has created
a series of
volcanoes in the Pacific.
Hotspots develop... when magma burns holes through rocks. The
Hawaiian Islands were created by hot spots.
Magma gets to the surface.. by moving
rocks. Gas pressure
in the magma cracks
overlying rocks. This is the reason
earthquakes
precede eruptions.
A lava
fountain can propel
lava 1,000 - 2,000 feet above a volcano.
People who live near Strato volcanoes...
are
faced with ash, cinders, high domes and earthquakes. The steep
volcanic
slopes... combined with rain, earthquakes, and lava, produce landslides,
avalanches and mudflows.
Shield
volcanoes
(found in Hawaii), have gentle slopes.
Ninety percent of
the material expelled from this volcano is lava... not pyroclastic.
Shield
volcanoes were formed by hotspot volcanism.
Fissure volcanoes or monogenetic fields... have hundreds
or
thousands of vents. These volcanoes have no
main
pathway to
expel
their lava. The American Southwest,
Mexico
and the San Francisco volcanic fields, are
examples
of this type of volcano.
Flood basalts are
another form of volcano. These volcanoes
can have lava
flows
50 meters thick. They cover SE Washington
State
and Oregon.
Caldera volcanoes explode.
They blow themselves up
and collapse their domes. The last big bang Caldera...
occurred in 83 A.D.
Types of Eruptions
Depending on the pressure that forces the
magna up, and
depending on the
viscosity (how
liquid the magma is) and
amount
of gas
in the
magna, eruptions vary in size,
explosiveness and
danger. Plinian eruptions
are the most dangerous
and explosive.
the magma is high in viscosity
and
gas content, and can
cause a
lava plume
over 10 miles high in the air. The Pompeii explosion of Mount Vesuvius... is an example,
of a Plinian eruption.
Effusive eruptions
are defined as those which have
lava outpouring onto the ground.
These eruptions are less
dangerous, and the
magma has lower
viscosity and levels of gas.
Lava flows generated
by effusive
eruptions...
vary in shape,
thickness, length and width. Strombolian eruptions... are
characterized
by the
intermittent
explosion or fountaining
of lava,
from a single
vent or crater. Each
episode is caused by the release of volcanic
gases, and they typically occur every few
minutes
or so, sometimes rhythmically and
sometimes irregularly.
Hydrovolcanic eruptions... are when volcanic
eruptions occur
near
oceans, saturated clouds
or other wet areas, the interaction of
water
and magma, can create a unique sort
of
eruptive column.
The hot magma heats the water, so that it becomes steam.
This rapid change of state,
causes an
explosive type of expansion
in the
water, which breaks apart the magma, creating a fine ash.
Fissure eruptions,
occur when magma flows
up through cracks in
the ground and leaks
out
onto the surface. These often occur
where plate movement has caused large fractures... in the earth's crust, and may also
spring up
around
the base of a volcano
with
a central vent.
Geophysicists used to think that the movement
of magma...
from the base of the crust, and
then out of the
volcano
in an eruption... took centuries or more.
In the last decade or so, however, researchers
have found
evidence, that volcanism is a
much more dynamic, rapid
process.
On time scales of days or weeks, for magma to
move
from a magma chamber and then
up to the surface to
erupt.
The world's most explosive
and devastating volcanic eruptions usually occur in subduction zones, because oceanic plates are
soaked with water, and that water... helps the overlying rock to melt. Ultimately,
the result is
a particularly,
"gassy" magma.
This Andes tic magma, as it is called, is very viscous... that is, resistant to flow
like maple
syrup, compared to
water. Such is the case, in the Cascades Range...
of
the Pacific Northwest, the home
of Mount St.
Helen's and 14 other
large volcanoes.
Andes tic magma,
is not explosive
in and
of itself.
But it does impede the escape of
gases... out of the magma chamber. Their migration,
being inhibited, causes their gases
to form bubbles and pockets in the magma.
Eventually, the pressure of the collected gases... rises so high,
that they
blow through the magma...
like a cork out of a
champagne bottle. The result
is an explosion of gas, ash, and
fiery fragments of volcanic rock.
Explosive volcanoes typically have a characteristic shape...
which is tall, with
a steep summit, created
out of alternating
layers of lava and volcanic rock fragments known as a composite
cone or strato volcano.
Many of history's most famous volcanoes... Etna, Vesuvius,
St. Helens, Fujiyama,
Arenal... are strato volcanoes.
Very rapidly formed volcanoes,
like "Paricutin" in Mexico, are
often a type known as a cinder cone... built out of layers, of
ejected volcanic rock. These volcanoes are typically no more than
1,000 or so
feet tall, whereas... strato
volcanoes, can become mountains.
Most of the damage... in strato volcano eruptions,
comes not from lava flow... but
from a phenomenon, known
as "pyroclastic" flow.
A "pyroclastic" flow, is an avalanche... of ground-hugging,
hot rock... accompanied by a cloud of
ash and gas... that
races down
the slope of
a volcano.
The flow can reach speeds
of up to
60 miles per hour, and temperatures of nearly 1,300 degrees
Fahrenheit.
Pyroclastic flows, cause more death and
destruction... than
any other volcanic hazard.
In 1902, on the Caribbean island of Martinique,
a
pyroclastic flow...
generated by the eruption
of Mt. Pelée...
swept into the town of St.
Pierre...
and incinerated 29,000
people.
The devastating mudflow,
that killed 25,000 people in
Armaro, Colombia, after the
1985 eruption of "Nevado del Ruiz" Volcano, (described in the "SAVAGE EARTH" program...
"Out of the Inferno"), was
triggered by a pyroclastic flow.
Pyroclastic flow and lava
aren't the only hazards created by
volcanic eruptions. Other dangers are "lahars"
mixtures of rock fragments
and water, that flood down volcanoes (mudflows, are
one type),
as well as landslides,
gas emissions, and ash
clouds.
Ash clouds, are a particular
problem for aircraft.
They can cause engine failure, damage electrical
systems,
scratch
the outer surface of a plane,
and contaminate its
interior.
Lightning Volcano
The effects of a volcanic eruption...
can also be felt
over the long term. Eruptions, releasing high concentrations of sulfur-rich "gas"
like the eruptions of the Philippines'
"Mount Pinatubo", in 1991,
and Mexico's "El Chichón", in 1982,
can alter global
climate.
The sulfur mixes with water vapor in the atmosphere
and forms clouds,
of sulfuric acid. The acid droplets, absorb incoming solar
radiation
and bounce it back into space.
The result: lower temperatures.
In the year after the eruption... of Pinatubo, global
temperatures dipped, by nearly a degree.
Of course, volcanoes aren't always associated
with
plate
boundaries.
Volcano chains, like the Hawaiian
Islands... are formed
by plumes of hot mantle, material... that rise up from the
mantle and intrude on weak parts
of the
crust, within the interior of a plate. The plumes are
called "hot spots."
Hot-spot volcanoes,
like those in Hawaii... often
form a
characteristic broad, flat shape, like that
of a
warrior's shield,
and are known as shield volcanoes.
Hawaii's Mount Kilauea...
has essentially been continuously erupting since 1983, which has
made
it an ideal test site for
a new system
to predict volcanic eruptions.
The system, first tested by researchers... from
Stanford University,
in January 1997, uses a
network of receivers...
hooked into the
satellite Global
Positioning System.
By looking at the position
of the receivers,
which can be determined
within a fraction
of an inch,
researchers can determine, if the
ground beneath the volcano... is shifting or deforming, as it would,
if it were
filling with
magma.
Other "tell-tale" signs of impending eruption... such as particular changes in gas emissions, and the frequency of earthquakes
are currently being studied by researchers,
at other volcanoes.
In the test,
researchers did see signs... that the ground
swelled, by as much as eight inches, in the hours before an eruption on January 30.
At the time, however, their system was not
working in real-time,
so they didn't see the signals until after the
eruption. Soon,
however, they hope to be able to
actually predict eruptions.
|
An Ancient Volcano...
