Krakatoa
Krakatoa (Indonesian name: Krakatau, Portuguese name: Krakatao) is a volcanic island in the Sunda
Strait between Java and Sumatra
in Indonesia.
The name is used for the island group, the main island (also
called Rakata),
and the volcano
as a whole. It has erupted repeatedly, massively and with disastrous consequences
throughout recorded history. The best known eruption culminated in a series
of massive explosions on August 26-27, 1883.
The 1883 eruption ejected more than 25 cubic kilometres of rock, ash, and pumice [1],
and generated the loudest sound ever historically reported — the cataclysmic
explosion was distinctly heard as far away as Perth in Australia
(approx. 1930 miles or 3100 km), and the island of Rodrigues near Mauritius
(approx. 3000 miles or 4800 km). Atmospheric shock waves reverberated around
the world seven times and were detectable for five days[2].
Near Krakatoa, according to official records, 165 villages and towns were
destroyed and 132 seriously damaged, at least 36,417 (official toll) people
died, and many thousands were injured by the eruption, mostly in the tsunamis
which followed the explosion.
The eruption destroyed two-thirds of the island of Krakatoa.
New eruptions at the volcano since 1927 have built
a new island, called Anak Krakatau (child of Krakatoa).
Origin and spelling of the name
The earliest mention of the island in the Western
world was on a map by Lucas Janszoon Waghenaer,
who labelled the island "Pulo Carcata." ("Pulo" is a form of pulau,
the Indonesian word for "island".) There are
two generally accepted spellings, Krakatoa and Krakatau. While
Krakatoa is more common in the English-speaking
world, Krakatau (or Krakatao in an older Portuguese based spelling)
tends to be favored by Indonesians. The origin of the spelling Krakatoa
is unclear, but may have been the result of a typographical error made in
a British source reporting on the massive eruption
of 1883.
Theories as to the origin of the Indonesian name Krakatau
include:
There is a popular story that Krakatau was the
result of a linguistic error. According to legend, "Krakatau" was adopted
when a visiting ship's captain asked a local inhabitant the island's name,
and the latter replied "Kaga tau" — a Jakartan/Betawinese
slang phrase meaning "I don't know". This story is largely discounted; it
closely resembles famous linguistic myths about the origin of the word kangaroo
and the name of the Yucatán Peninsula.
The name is spelled Karata on a map drawn before
1708. [citation needed]
Before 1883
Geography
Before the 1883 eruption, Krakatoa consisted of three
main islands: Lang ('Long', now called Rakata Kecil or Panjang) and Verlaten
('Forsaken' or 'Deserted', now Sertung), which were edge remnants of a
previous very large caldera-forming eruption; and Krakatoa itself,
an island 9 km long by 5 km wide. Also there was a tree-covered islet near
Lang named Poolsche Hoed ('Polish Hat', apparently because
it looked like one from the sea), and several small rocks or banks between
Krakatoa and Verlaten. There were three volcanic cones on Krakatoa: running
South to North they were: Rakata (823 m), Danan (445 m),
and Perboewatan (also spelled Perbuatan) (122 m). (Danan
may have been a twin volcano). Krakatoa is directly
above the subduction zone of the Eurasian Plate and Indo-Australian Plate, where the plate
boundaries undertake a sharp change of direction, possibly resulting in an
unusually weak crust in the region.
416 AD event
The Javanese Book of
Kings (Pustaka Raja) records that in the year 338 Saka (416 AD) "A thundering
sound was heard from the mountain Batuwara ... a similar noise from Kapi
... The whole world was greatly shaken and violent thundering, accompanied
by heavy rain and storms took place, but not only did not this heavy rain
extinguish the eruption of the fire of the mountain Kapi, but augmented the
fire; the noise was fearful, at last the mountain Kapi with a tremendous
roar burst into pieces and sank into the deepest of the earth. The water
of the sea rose and inundated the land, the country to the east of the mountain
Batuwara, to the mountain Raja Basa, was inundated by the sea; the inhabitants
of the northern part of the Sunda country to the mountain Raja Basa were drowned
and swept away with all property[3]
... The water subsided but the land on which Kapi stood became sea, and Java
and Sumatra were divided into two parts." There is no geological evidence
of a Krakatoa eruption of this size around that time; it may describe loss
of land that previously joined Java to Sumatra across what is now the narrow
east end of the Sunda Strait; or it may be a mistaken date, referring
to an eruption
in 535 AD, also
referred to in the Javanese Book of
Kings, and for which there is geological and some corroborating historical
evidence.
535 AD event
David Keys and others have postulated
that the violent eruption of Krakatoa in 535 may have been responsible for
the global climate changes of 535-536. Keys
explores what he believes to be the radical and far ranging global effects
of just such a putative 6th century eruption in his book Catastrophe:
An Investigation into the Origins of Modern Civilization. Additionally,
in recent times, it has been argued that it was this eruption which created
the islands of Verlaten and Lang (remnants of the original) and the beginnings
of Rakata
— all indicators of early Krakatoa's caldera's
size. However, there seems to be little, if any,
datable charcoal from that eruption, even if there is plenty of circumstantial
evidence.
1600s
At least two Dutch travelers reported that Danan and
Perboewatan were seen erupting in May 1680 and February
1681.
Visit by the HMS Discovery
In February 1780, the crew of HMS Resolution and HMS
Discovery on the way home after Captain James
Cook's death in Hawaiʻi, stopped
for a few days on Krakatoa. They found two springs on the island, one fresh
water and the other hot. They described the natives who then lived on the
island as "friendly" and made several sketches. (In his journal, John
Ledyard calls the island 'Cocoterra'.)
Dutch activity
In 1809, the Dutch established a penal
colony on the islands. (No information on exactly where.) It was in operation
for about a decade.
In 1880, R.D.M. Verbeek made an official survey
of the islands and published a comprehensive report in 1884/5. This proved
helpful in judging the geological and biological impact of the 1883 eruption.
The 1883 eruption
Pre-eruption
In the years before the 1883 eruption, seismic activity
around the volcano was intense, with some earthquakes
felt as far distant as Australia. Beginning 20 May 1883, three months
before the final explosion, steam venting began to occur regularly from Perboewatan,
the northern of the island's three cones. Eruptions of ash reached an altitude
of 6 km (20,000 ft) and explosions could be heard in Batavia (Jakarta)
160 km (100 miles) away. Activity died down by the end of May. Also, to help
the eruption along, water seeped into the magma chamber and created large
amounts of steam and smoke.
Early eruptions
The volcano began erupting again around 19 June.
The seat of the eruption is believed to have been a new vent or vents which
formed between Perboewatan and Danan, more or less where the current volcanic
cone of Anak Krakatau is. The violence of the eruption caused tides in the
vicinity to be unusually high, and ships at anchor had to be moored with
chains as a result. On 11 August larger eruptions began, with ashy plumes
being emitted from at least eleven vents. On 24 August,
eruptions further intensified. At about 1pm (local time) on 26 August,
the volcano went into its paroxysmal
phase, and by 2pm observers could see a black cloud of ash 27 km (17 miles)
high. At this point, the eruption was virtually continuous and explosions
could be heard every ten minutes or so. Ships within 20 km (11 nautical
miles) of the volcano reported heavy ash fall, with pieces of hot pumice up
to 10 cm in diameter landing on their decks. A small tsunami
hit the shores of Java and Sumatra
some 40 km (28 miles) away between 6pm and 7pm.
Cataclysmic stage
On August 27, the volcano entered the final cataclysmic
stage of its eruption. Four enormous explosions took place at 5:30 a.m.,
6:42 a.m., 8:20 a.m., and 10:02 a.m. The worst and loudest of these was the
last explosion. Each was accompanied by very large tsunamis
believed to have been over 100 ft high in places. A large area of the Sunda
Strait and a number of places on the Sumatran coast were affected by
pyroclastic flows from the volcano. The explosions
were so violent that they were heard 2,200 statute
miles (3,500 km) away in Australia
and the island of Rodrigues near Mauritius,
4,800 km away; the sound of Krakatoa's destruction is believed to be the
loudest sound in recorded history, reaching levels of 180 dBSPL 100 miles
(160 km) away. Ash was propelled to a height of 50 miles (80 km). The eruptions
diminished rapidly after that point, and by the morning of August 28 Krakatoa
was quiet.
After eruptions
Small eruptions continued through October, and continued
to be reported through February 1884 (although any after mid-October were
discounted by Verbeek). In the aftermath of the eruption, it was found that
the island of Krakatoa had almost entirely disappeared, except for the southern
half of Rakata cone cut off along a vertical cliff, leaving behind a 250
m-deep caldera.
Effects
The combined effects of pyroclastic flows, volcanic ashes and tsunamis
had disastrous results in the region. There were no survivors from 3,000
people located at the island of Sebesi, about
13 km from Krakatoa. Pyroclastic flows killed around 1,000 people at Ketimbang on the coast of Sumatra some
40 km north from Krakatoa. The official death toll recorded by the Dutch
authorities was 36,417 and many settlements were destroyed, including Teluk Betung and Ketimbang in Sumatra,
and Sirik
and Semarang
in Java. The areas of Banten on
Java and the Lampong
on Sumatra
were devastated. There are numerous documented reports of groups of human
skeletons floating across the Indian
Ocean on rafts of volcanic pumice and
washing up on the east coast of Africa, up
to a year after the eruption. Some land on Java was never repopulated; it
reverted to jungle
and is now the Ujung Kulon National Park.
Tsunamis
Ships as far away as South
Africa rocked as tsunamis hit them, and the bodies of victims were found
floating in the ocean for weeks after the event. The tsunamis that accompanied
the eruption are believed to have been caused by gigantic pyroclastic flows entering the sea; each of
the five great explosions was accompanied by a massive pyroclastic flow resulting
from the gravitational collapse of the eruption column. This caused several
km³ of material to enter the sea, displacing an equally huge volume
of seawater. Some of the pyroclastic flows reached the Sumatran coast as
much as 25 miles (40 km) away, having apparently moved across the water on
a "cushion" of superheated steam. There are also indications of submarine
pyroclastic flows reaching 10 miles (15 km) from the volcano.
On a recent documentary, a German research team conducted
tests of pyroclastic flows moving over water. The tests revealed that hot
ash traveled over the water on a cloud of superheated steam, preceding a tsunami.
Geographic effects
As a result of the huge amount of material deposited
by the volcano, the surrounding ocean floor was drastically altered. It is
estimated that as much as 18-21 km³ of ignimbrite
was deposited over an area of 1.1 million km², largely filling the 30-40
m deep basin around Krakatoa. The land masses of Verlaten and Lang were increased,
and volcanic ash continues to be a significant part of the geological composition
of these islands. Polish Hat disappeared. A new rock islet called Bootsmansrots
('Bosun's
Rock', a fragment of Danan) was left.
Two nearby sandbanks
(called Steers and Calmeyer after the two naval officers who investigated
them) were built up into islands by ashfall, but the sea later washed them
away. Seawater on hot volcanic deposits on Steers and Calmeyer caused steam
which some people mistook for continued eruption.
The fate of Krakatoa itself has been the subject of
some dispute among geologists. It was originally proposed that the island
had been blown apart by the force of the eruption. However, most of the material
deposited by the volcano is clearly magmatic in origin and the caldera formed
by the eruption is not extensively filled with deposits from the 1883 eruption.
This indicates that the island subsided into an empty magma
chamber at the end of the eruption sequence, rather than having been
destroyed during the eruptions.
Worldwide effects
The eruption produced erratic weather and spectacular
sunsets throughout the world for many months afterwards, as a result of sunlight
reflected from suspended dust particles ejected by the volcano high into
Earth's atmosphere. This worldwide volcanic dust veil acted as a solar radiation
filter, reducing the amount of sunlight reaching the surface of the earth.
In the year following the eruption, global temperatures were lowered by as
much as 1.2 degrees Celsius on average. Weather patterns continued to be
chaotic for years, and temperatures did not return to normal until 1888.
British artist William Ashcroft made thousands of color sketches
of the red sunsets half-way around the world from Krakatoa in the years after
the eruption. In 2004, researchers proposed the idea that the blood-red
sky shown in Edvard Munch's famous 1893 painting
The Scream is also an accurate depiction of the
sky over Norway
after the eruption. Munch said: "suddenly the sky turned blood red ... I
stood there shaking with fear and felt an endless scream passing through
nature." Also a so called blue moon
had been seen for two years as a result of the eruption.
Legacy of the 1883 eruption
The 1883 eruption of Krakatoa is among the most violent
volcanic events in modern times (a VEI of 6, equivalent to 200 megatons
of TNT - about 13000 times the yield of the Little
Boy bomb which devastated Hiroshima, Japan). Concussive air waves from
the explosions travelled seven times around the world, and the sky was darkened
for days afterwards. Waves from the tsunamis were recorded as far away as
the English Channel. The explosion is considered
to be the loudest noise ever heard by man.
Cause of the explosion
The violence of the final explosions has also attracted
debate. Four theories are:
- Contemporary investigators believed that the volcano's
vents had sunk below sea level on the morning of 27 August, letting seawater
flood into it and causing a massive series of phreatic
(interaction of ground water and magma) explosions.
- The seawater could have chilled the magma, causing
it to crust over and producing a "pressure cooker" effect relieved only when
explosive pressures were reached.
- Both these ideas assumed that the island subsided
before the explosions; however, the evidence does not support that conclusion
and the pumice and ignimbrite deposits are not of a kind consistent with
a magma-seawater interaction.
- A massive underwater land slump or partial subsidence
suddenly left the highly pressurized magma chamber wide open.
- The final explosions may have been caused by magma mixing caused by a sudden infusion
of hot basaltic magma into the cooler and lighter magma in the chamber below
the volcano. This would have resulted in a rapid and unsustainable increase
in pressure, leading to a cataclysmic explosion. Evidence for this theory
is the existence of pumice consisting of light and dark material, the dark
material being of much hotter origin. However, such material reportedly is
less than 5% of the content of the Krakatoa ignimbrite
and some investigators have rejected this as a prime cause of the 27 August
explosions.
Subsequent volcanism
Anak Krakatau, June 2005. Fresh lava flows are clearly visible.
Map of Krakatoa as it is today, showing boundaries of the ancient caldera
in which the island sits
Verbeek investigation
Although the violent engulfment phase of the eruption
was over by late afternoon of August 27,
after light returned by the 29th, reports continued for months that Krakatoa
was still in eruption. One of the earliest duties of Verbeek's committee
was to determine if this was true and also verify reports of other volcanoes
erupting on Java and Sumatra. In general, these were found to be false, and
Verbeek discounted any claims of Krakatoa still erupting after mid-October
as due to steaming of hot material, landslides due to heavy monsoon rains
that season, and "hallucinations due to electrical activity" seen from a
distance.
No signs of activity were seen in the next several years
until 1913, when an eruption was reported. Investigation could find no evidence
the volcano was awakening, and it was determined that what had been mistaken
for renewed activity had been a major landslide (possibly the one that formed
the second arc to Rakata's cliff).
Anak Krakatau
Verbeek, in his report on the eruption, predicted that
any new activity would manifest itself in the region that had been between
Perboewatan and Danan. This prediction came true in June 1927 when evidence
of a submarine eruption was seen in this area. A few days later, a new island
volcano, named Anak Krakatau ("Child of Krakatoa"), broke water. Initially,
the eruptions were of pumice and ash, and it (and 2 more islands) was quickly
eroded away by the sea; but eventually Anak Krakatoa 4 produced lava flows
faster than the waves could erode them. Of considerable interest to volcanologists,
this has been the subject of extensive study since the new island broke water
permanently in August 1930.
Current activity
The island is still active, with its most recent eruptive
episode having begun in 1994. Since then, quiet periods of a few days have
alternated with almost continuous eruptions, with occasional much larger
explosions. Since the 1950s, the island has grown at an average rate of five
inches (13 cm)
per week. Reports in 2005 indicated that activity at Anak Krakatau was increasing,
with fresh lava flows adding to the island's area.
Biological research
The islands have become a major case study of island
biogeography and founder populations in an ecosystem being
built from the ground up in an environment virtually sterilized.
'The Krakatau problem'
Biologically, the 'Krakatau problem' refers to the question
if the islands were completely sterilized by the 1883 eruption, or if some
life survived. When the first researchers reached the islands in May, 1884,
the only living thing they found was a spider in a crevice on the south side
of Rakata. Life quickly recolonized the islands, however. The eastern side
of the island has been extensively vegetated by trees and shrubs, presumably
brought there as seeds washed up by ocean currents or carried in birds' droppings.
It is, however, in a somewhat fragile position and the vegetated area has
been badly damaged by recent eruptions.
Media
The volcano has inspired several books and films.
About the volcano
Books
- Tom Simkin and Richard Fiskes' book about Krakatoa
was written close to the centenary of the event and provides source material
that had previously been unavailable in English, as well as to that point
the most thoroughly researched book on the subject, and it has not been surpassed.
- Simon Winchester explores the eruption of Krakatoa
in his book Krakatoa: The Day the World Exploded, 27 August 1883.
The book examines the history of the region, the early spice trade,
the growth of colonial governments, explains the geology of volcanos and
describes in detail the series of eruptions and tsunamis
and their effects around the globe.
Film
- Krakatoa, a short 1933 movie about
the volcano that won the Academy Award for Best Short Subject, Novelty
for its producer Joe Rock. This movie was notable for overwhelming the
sound
systems of the cinemas of the time. In Australia,
the distributors insisted on a power output of 10 watts RMS as a minimum
for cinemas wishing to show the movie. This was then considered a large system,
and forced many cinemas to upgrade.
- The eruption is the subject of a 1969 Hollywood
film starring Maximilian Schell, which was titled Krakatoa, East of Java — even though
Krakatoa is in fact west of Java. This blatant error is perhaps the
most remembered thing about the film. (Tambora,
on Sumbawa,
is the violent volcano east of Java). There was a novelization with
the same title by Micheal Avallone.
Television
- Ultimate Blast: Eruption at Krakatau has been
aired on Discovery Channel, as part of the Moments
in Time series.
- The 1883 eruption is reconstructed in the BBC drama
'Krakatoa - The Last Days', first broadcast
in May 2006. It was broadcast in the U.S. as Krakatoa: Volcano of Destruction
on the Discovery Channel
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