Transcript Kr - Tricia Abrizenski

Tricia Abrizenski
11.05.10
Natural Disasters 1750-91
Fall 2010
In this presentation we will discuss:
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What Krakatoa was

It’s Location
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How Krakatoa was created
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Events leading up to the eruption
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The result of the eruption
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The preliminary eruption
investigation
The devastation caused
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Why Krakatoa erupted so
forcefully
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Krakatoa today
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The effects of the Krakatoa
eruption
Sound and pressure waves from
the eruption
Anak Krakatau in the future
What was Krakatoa?
Krakatoa was a chain of
three stratovolcano islands
with five identified
evolutionary periods.
Over time it grew to
become one giant island
volcano with 3 peaks.
It was located in the most
volcanically active region
on earth (Indonesia) south
of Sumatra (approximately
25 miles from Ketimbang)
and west of Java in the
Sunda Strait.
It is also one of the
deadliest volcanoes in
history.
Slide 23 – 1
Slide 25 - 1
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After remaining dormant for more than
200 years, it would erupt in a cataclysmic
explosion during the summer of 1883 after
months of geologic activity signifying the
reawakening of the island.
The pyroclastic flows and ensuing
tsunamis that it produced would claim the
lives of 36,417 people and injure thousands
more in the region; it would become
known as one of (if not the) most
important eruptions in the fields of science
and volcanology.
It has been confirmed through
the reading of sulfuric acid
deposits contained within
Antarctic ice core samples that
Krakatoa erupted with
paroxysmal force in 535AD.
The entire island was wiped
from the surface of the earth
forming a large undersea
caldera, thus ending the first
evolutionary period of
Krakatoa and beginning the
second.
During its 3rd period
Krakatoa would rebuild itself
with a series of regular,
violent, undersea eruptions
forming three volcanic peaks.
The volcanoes Rakata (798m),
Danan (500m), and
Perbuwaten also known as
Perboewetan (130m) would
grow together, from the
original caldera of the
ancestral Krakatau, to create
the larger island of Krakatoa.
Slide 23 - 2
Krakatoa was formed through the process of undersea subduction between the
Indo-Australian plate and the Burmese continental plate.
As one tectonic plate subducts under another, magma can find its way to the
surface and form volcanoes.
As the older, cooler
oceanic plate was
pushed below the
warmer, more
buoyant continental
plate the cooler rock
was reabsorbed into
the core of the planet.
As that rock melted it
found its way to the
surface through
cracks and fissures in
the earth’s crust
erupting violently to
create Krakatoa.
Slide 23 – 3
Slide 25 - 2
In Ketimbang (23miles NW) and Batavia (83 miles E of Krakatoa) there
were precursors to the events that would take place only a short time
later.
Small indiscernible tremors were taking place below the earth’s crust at
that time.
Batavia was the capital of the Dutch East Indies; it was also home to a
meteorological observatory. The chief Dr. and Director there was Dr.
Vanderstock. He was responsible for monitoring the seismic activity in
the region and it is widely believed that through his initial observations
in the early stages of the eruption of Krakatoa, he helped modern
volcanologists understand why the volcano erupted with such
paroxysmal force.
There was also a young geologist stationed at the observatory by the
name of Sherman.
Slide 23 - 4
On May 9th in Ketimbang, four months before the eruption that
would destroy Krakatoa, there was a great tremor felt throughout
the region. At the time, it was unknown as to where it had come
from or what the cause was but is now believed to be the first
discernable sign that intensely pressurized magma had broken
through a fault underneath the volcano and was making its way to
the surface of the earth’s crust.
Eleven days later on May 20th, fisherman hunting off of the coast of
Krakatoa and foraging in the jungle for timber to build boats
witnessed the first eruption.
Perbuwaten, the smallest volcano on the island, had erupted
throwing ash and pumice miles from its peak in a vulcanian
eruption.
The eruption was also witnessed by Captain Johan Lindeman of the
Governor General Loudon.
The Governor General Loudon was a Dutch steamship that often
passed through the Sunda Strait and within close range of Krakatoa.
Slide 23 - 5
Only a fraction of a moment after the eruption the shockwaves
reached Ketimbang and minutes after that, the shockwave was
recorded within Dr. Vanderstocks observatory in Batavia.
Dr. Vanderstock read the recording, much like we would a readout
from a seismometer today, and came to the conclusion that the
shockwave had come not through the ground, but through the air
from some 100 miles away.
It was Sherman who deduced that the shockwave must have then
come from a volcano.
Dr. Vanderstock was notified of the eruption definitively by the
controller of Ketimbang, Willem Beijerinck. Vanderstock then
notified the Governor General who subsequently ordered an
investigatory expedition to the island.
Slide 23 – 6,7
The expedition was led by Sherman and began on May 27th 1883.
Upon their arrival they found that the entire forest on the
Perbuwaten side of the island had been flattened and charred by
what we now know are pyroclastic flows.
Pyroclastic flows are superheated fluid masses of rock , gas, and ash
that move in a rapid gravitational manner across land and water.
The expedition yielded volcanic and geologic samples of great
importance such as water, ash, acids, and large pumices that had
been strewn across the beaches and riddled with small holes formed
from the gaseous content of the lava.
Sherman’s report to the Governor General offered information such
as there were no obstacles to hinder their investigation other than
loose ash and foul smelling smoke that caused them to gag.
Slide 23 - 8
Over the preceding months the island had returned to a relatively calm state;
then on August 26th at 1:06 PM, the Island volcano of Krakatoa began to erupt
in true plinian fashion.
All three craters on the island began to erupt and with the ejection of magma,
pumice, and ash, day became night and the clouds blocked out the sun so
that you may not see your hand in front of your face.
Gas, ash, and pumice were
ejected so high into the
atmosphere that it joined with
the jet stream and was carried
around the globe for years to
come affecting everything from
the global climate and weather
patterns to the colorations of the
sunrise and sunset.
It is even thought that the famous
“Scream” painting was inspired by
the colors seen in the sky half way
around the world soon after the
eruption.
Slide 25 - 3
The following morning, at 5:30 AM,
began another series of eruptions on
Krakatoa that inevitably ripped the
island volcano apart with paroxysmal
force, completely destroying it and
leaving only remnants of Rakata
behind after collapsing back into the
ocean.
The eruption scattered debris across
the Indian Ocean as far away as
Madagascar.
It was loud enough to be heard over
more than 8% of the earth’s surface
And the air borne shock waves
reverberated around the entire planet
7 times
The actual force of the explosion is
somewhat debatable; some reports
say that it was equivalent to 200
megatons of TNT, some report that
it was equal to 1,000 atomic bombs,
and others yet say that it was a force
near 21,000 megatons of nuclear
explosion.
The one thing that is not debatable is
the level of destruction left in the
wake of the volcanic eruptions and
pyroclastic flows that burned
thousands, were approximately
2,800 ft. high in their origination and
stretched more than 25 miles from
the island of Krakatoa to the
mainland in Ketimbang as well as
the following tsunamis that claimed
more than 36,000 lives.
Slide 23 – 9, 10, 11
Pyroclastic Flows
Some investigation as to the interaction of
pyroclastic flows and water can be viewed in
this excerpt from the Discovery Channel
documentary regarding Krakatoa.
Click for 3:17 Video
In this video we can see one of the possible
results of a pyroclastic flow and its interaction
with the surrounding water.
Slide 23 – 12
Slide 25 - 4
As the flow cascades down the
mountainside and comes into
contact with the water, the
heavier debris moves outward
and sinks; however the
forward momentum of the
flow causes a large wave to
form.
In addition, the superheated
ash on the surface comes into
contact with the water and
creates a cloud of steam for the
lighter debris to flow on top of
enabling it to move greater
distances and at an even more
rapid pace than it would have
on land.
The tsunamis that followed the eruption were reported to be more than 40 meters high.
Slide 25 - 5
As the tsunami continued to
move inland, it lost speed but
gained in height.
As it hit the Sumatran coastline it
was then funneled up Lampong
Bay destroying everything in its
path.
It carried the Dutch steamer Berouw
1.8 miles inland of Telok Betong
before finally depositing it across a
river bed.
Slide 23 – 13
Slide 25 - 6
Slide 25 – 7S
The Destruction of
Fourth Point
Lighthouse
The tsunami that hit the
coastline at Java even tore up
large chunks of sea bed and
coral reported to have weighed
some 600 tons.
One of these chunks of coral
was responsible for the
destruction of the Fourth Point
Lighthouse.
600 Ton coral that destroyed Fourth Point Lighthouse
The new lighthouse that was
built is 40 meters in height and
is about the same height as the
tallest tsunami wave that hit the
coastline there.
An estimated 19.6 thousand
Javanese died in the tsunami
Slide 23 – 13
Slide 25 - 7
Same coral responsible for the destruction of Fourth Point lighthouse today
But WHY?
WHY did Krakatoa erupt
so forcefully?
That question has puzzled
scientists for decades.
Numerous scientists, both
volcanologists as well as
geologists, have made
repeat visits to Rakata (all
that remains of Krakatoa)
to find answers to this very
question.
It seems as though there
are a number of factors that
come to play in the violent
eruption of Krakatoa.
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Krakatoa is situated atop a
subduction plate within the “Ring
of Fire”.
Its construction was that of a
stratovolcano who’s chamber
contained thick, viscous, silica rich,
andesitic magma.
Krakatoa was not comprised of
“solid” rock but made up of fairly
loose debris formed over time from
layers of pumice and pyroclastic
activity topped with lava flows of a
high viscosity.
The alternating layers would make
it easier for the volcano to crumble
and collapse after an exceptionally
explosive eruption.
The high viscosity lava that formed
the cap of the volcano was what
held in the pressure over hundreds
of years.
Slide 23 - 14
After the initial eruption the magma chamber of the volcano was partially
emptied and the thick viscous magma formed over the cap again allowing for
the lull in activity for a few months. When the magma chamber emptied the
fissure that had opened previously underneath the volcano allowed for
superheated magma to flow into the volcano and mix with the cooler magma
in the chamber, as is evident from the examination of larger pumices on
Rakata.
The cooler magma that had
been sitting in the chamber for
an extended period is lighter in
color than the hotter magma
that entered the chamber later
after the initial eruption. When
examining the pumices it has a
marbled effect of lighter and
darker (or cooler and hotter)
magma types.
Slide 23 – 15
Slide 25 - 7
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May 9th violent tremors are felt in the region. It is believed that a
fissure opened under the volcano at this time.
May 20th Perbuwaten erupts as a result of the open fissure and
partially empties the magma chamber.
A new “plug” forms over the volcano due to the viscous nature of
the lava allowing for a lull in activity and time for the magma
chamber refill.
Superheated magma enters the chamber mixing with cooler
magma already in the chamber and melting surrounding rock
releasing more gasses and building pressure inside of the volcano.
This eruption process has been likened to shaking up a bottle of
champagne until the cork blows off.
The superheated magma directly caused the pressure inside of the
volcano to rise until the structural integrity of the volcano failed
and erupted with cataclysmic force blowing the island apart.
The island then collapsed into the magma chamber creating an
undersea caldera approximately 3X5 miles across.
Sound & Pressure
Waves
The explosion of Krakatoa at 10:02
AM August 27th 1883 has been
renowned as the loudest sound
ever heard by modern humans.
It was heard over more than 1/12th
of the earth’s surface; 2,000 miles
away in Perth Australia, as well as
3,000 miles away at Rodriguez
Island in the Indian Ocean.
It is the longest distance traveled
by any airborne sound in recorded
history.
It also produces pressure waves
that reverberated around the globe
seven times and were recorded
over a period of 12 days.
The Fourth and final explosion at
10:45 AM tore Krakatoa apart and
the volcanic island collapsed back
into the sea.
Map of atmospheric pressure waves from the Krakatoa eruption.
Slide 23 – 16
Slide 25 - 8
The news of the eruption of
Krakatoa and subsequent
disappearance was transmitted
around the globe in a matter of
hours through the use of fairly
newly installed transoceanic
telegraph cables.
People around the world would
soon (and for years thereafter)
take note of the effects of the 11
cubic miles of ash and debris that
had joined with the atmosphere.
Sunset Oil Pastels drawn after the eruption.
Evidence that the explosion
affected the atmosphere for 4-5
years afterwards is documented in
detail at The Royal Society in
London
Slide 23 – 17
Slide 25 – 9, 10
Now, nearly 130 years later,
Krakatoa is in its 5th evolutionary
stage.
In June of 1927 a new volcano called
Anak-Krakatau was born from the
undersea caldera that remains from
earlier explosions.
It is regularly active, as well as
continually and rapidly growing at a
rate of 12+ feet per year.
It first developed through a number
of submarine eruptions and now
stands at a height of more than 1,033
feet. It covers 1.25 square miles and
in less than 10 years ejected more
than 50 million tons of material.
Slide 23 – 18
Slide 25 - 11
The investigation of Krakatoa and Anak-Krakatau continues today
and also continues to influence volcanism as the first ever widely
studied eruption in history.
Anak-Krakatau will continue to grow and it WILL erupt again…
whether or not it will be as destructive a force as its parent, still
remains to be seen but is almost a certainty.
Slide 23 - 18
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Carter, S. (Producer), Hall, J. (Writer), & Hall, J. (Director). (2005). Krakatoa [Motion Picture]. USA: PBS
Carter, S., Marsh, S. (Producers), & Strange, R. (Director). (2009). How the Earth was Made: Krakatoa [Motion Picture]. USA / UK: A&E Television
Networks
2.
How the Earth was made: Krakatoa, History Channel Documentary, 2009. Global Volcanism Program of the Smithsonian Institute
http://www.volcano.si.edu
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5.
Krakatoa Documentary, PBS, 2005. How the Earth was made: Krakatoa, History Channel Documentary, 2009
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12.
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13.
Krakatoa Documentary, PBS, 2005. How the Earth was made: Krakatoa, History Channel Documentary, 2009
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Krakatoa Documentary, PBS, 2005. Krakatoa: Volcano of Destruction, Discovery (BBC), 2006
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How the Earth was made: Krakatoa, History Channel Documentary, 2009
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Abbott, P. L. (2009). Natural Disasters (7th ed.). New York, NY, USA:
McGraw Hill.
Beijerinck, J. (2010, 10 25). Discovery Channel :: Krakatoa :: Survivor Diary ::
Johanna Beyerinck. Retrieved 10 25, 2010, from Discovery Channel:
http://dsc.discovery.com/convergence/krakatoa/diaries/johanna.html
Carter, S. (Producer), Hall, J. (Writer), & Hall, J. (Director). (2005). Krakatoa
[Motion Picture]. USA: PBS.
Evans, G., Mosley, M. J. (Producers), Heber-Percy, C., Olmert, M.
(Writers), & Miller, S. (Director). (2006). Krakatoa: Volcano of Destruction
[Motion Picture]. UK: Discovery Channel.
Carter, S., Marsh, S. (Producers), & Strange, R. (Director). (2009). How the
Earth was Made: Krakatoa [Motion Picture]. USA / UK: A&E Television
Networks.
Unk. (2010, 10 27). Krakatau. Retrieved 10 27, 2010, from Smithsonian
Institution - Global Volcanism Program: Worldwide Holocene Volcano
and Eruption Information: http://www.volcano.si.edu
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4.
Evans, G., Mosley, M. J. (Producers), Heber-Percy, C., Olmert, M. (Writers), & Miller, S. (Director). (2006).
Krakatoa: Volcano of Destruction [Motion Picture]. UK: Discovery Channel
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6.
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7.
Evans, G., Mosley, M. J. (Producers), Heber-Percy, C., Olmert, M. (Writers), & Miller, S. (Director). (2006).
Krakatoa: Volcano of Destruction [Motion Picture]. UK: Discovery Channel
8.
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10.
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11.
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