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The
Great Explosion of the Krakatau Volcano ("Krakatoa")
of August 26, 1883, in Indonesia
George Pararas-Carayannis
(Excerpts from
"Some of the World's Greatest Disasters", a book under
preparation)
©
2001 George Pararas-Carayannis / all rights reserved
 
Selected
by Los Angeles Times and the National Science Teachers Association
(NSTA)
 Introduction
 Over a century ago, on August
26,1883, the island volcano of Krakatau ("Krakatoa")
in Indonesia, a virtually unknown volcanic island with a history
of violent volcanic activity, exploded with devastating fury.
The eruption was one of the most catastrophic natural disasters
in recorded history. The effects were experienced on a global
scale. Fine ashes from the eruption were carried by upper level
winds as far away as New York City. The explosion was heard more
than 3000 miles away. Volcanic dust blew into the upper atmosphere
affecting incoming solar radiation and the earth's weather for
several years.
A series of large
tsunami waves generated by the main explosion, some reaching
a height of nearly 40 meters (more than 120 feet) above sea level,
killed more than 36,000 people in the coastal towns and villages
along the Sunda Strait on Java and Sumatra islands. Tsunami waves
were recorded or observed throughout the Indian Ocean, the Pacific
Ocean, the American West Coast, South America, and even as far
away as the English Channel.
Location and Geologic
Setting of the Krakatau (Krakatoa) Volcano
 Krakatau
(Krakatoa) is located in the Sunda Strait, 40 km off the west
coast of Java on the island of Rakata in Indonesia. The geographical
coordinates of Krakatoa are 16.7 S. Latitude and 105.4 E. Longitude.
Krakatoa is one of the volcanoes of the Sunda volcanic arc. The
volcano was formed by the subduction of the Indian-Australia
Plate under the Eurasian Plate.
At its peak, Krakatoa
reached a height of 790 m (2,600 ft.) above sea level. Its first
known eruption occurred in 416 A. D. However, this eruption
destroyed the volcano of Krakatoa which collapsed and formed
a 4-mile wide caldera. The islands of Verlaten and Lang are remnants
of this older volcano. Subsequently, three volcanoes combined
to form the island of Krakatau.
Thus Krakatoa was
the remnant of the old volcano which had not erupted for 200
years. Prior to the great 1883 eruption of Krakatoa, Rakata island
was made of three volcanoes and at least one older caldera. The
volcanic cones aligned in a north-south direction. The northernmost
was called Poeboewetan and the southernmost was called Rakata.
Overall approximate dimensions of Krakatoa were 5 by 9 Kilometers.
Chronology of Events
Prior to the Great August 26, 1883 Eruption
After a long period
of inactivity (about 200 years), Krakatoa became active again
in early 1883. The first indication that something was happening
on Krakatoa was when a large earthquake struck the area. Seismic
activity became stronger until May 20,1883, when the volcano
abruptly came to life. The initial explosive eruptions of Krakatoa
could be heard 160 km away. Steam and ash could be seen rising
11km above the summit of the volcano. By August 11, 1883. three
vents were actively erupting. Eleven other vents were ejecting
smaller quantities of steam, ash and dust.
Around 1 pm on the
26th of August 1883, the explosions became more frequent occurring
on the average every 10 minutes. Sailors on a ship, 120 km away
from the island reported a black cloud of smoke rising above
the volcano. At the time the rim of Krakatoa's crater was approximately
1,000 meters in diameter and had and average depth of 50 meters.
The volcano' s central vent was blocked by a plug of solid lava
and underneath it pressure was rapidly building up.
The Great Eruption
 The
renewed activity in May 1883 culminated in four gigantic explosions
on August 26 and 27 of the same year. On the afternoon of August
26, 1883, (27 August local date) at 17: 07 Greenwich time (GMT),
the first of these four violent explosions begun. A black cloud
of ash was initially observed. It rose 17 miles (27 kilometers)
above Krakatoa. In the morning of the next day, on August 27,
1883, at 05:30, 06:44 and 10:02 GMT, three more violent eruptions
occurred. It was the paroxysmal eruption which occurred at 10:02
which blew away the northern two-thirds of the island. This was
the most severe violent volcanic explosion on Earth in modern
times. The explosion was followed by the collapse of the unsupported
volcanic chambers of Krakatoa forming the huge underwater caldera.
It was this explosion and collapse of Krakatoa that generated
catastrophic tsunami waves as high as 37 meters. (120 ft.) that
caused havoc and destruction in the Sunda Strait.
Photo of the Krakatoa
eruptive activity a few hours before the major explosions (taken
on August 26, 1883 from a ship crossing the Sunda Strait.
A Phreatomagmatic Event
Krakatoa's paroxysmal
explosion was "phreatomagmatic" . Ocean water entered
the magmatic chambers of the volcano when its walls begun to
rupture. Super heated steam built tremendous pressure which,
in turn, resulted in the large explosion of the volcano. The
violent explosion of released gases blasted huge quantities of
ash, cinders, pumice, bombs, and larger blocks skyward. The explosion
was followed by the collapse of the volcanic remnants into the
empty magmatic chambers, thus forming a submerged caldera.
 Magnitude of the 1883 Eruption
of Krakatoa
The 1883 eruption
of Krakatoa has been assigned a Volcanic Explosivity Index or
VEI of 6 which rates as "colossal". To be assigned
a VEI rating of 6, a volcanic eruption must have a plume height
over 25 km and a displacement volume ranging between 10 and 100
km3 (cubic kilometers). Eruptions of this size occur only once
every few hundred years on earth.
The total energy released
by the four main events of the 1883 eruption was equivalent to
200 megatons of TNT. Most of this energy was released by the
third paroxysmal explosion which has been estimated to be equivalent
to an explosion of 150 megatons of TNT. To understand the magnitude
of the Krakatoa explosion, it will suffice to say that the Hiroshima
atomic bomb was only about 20 kilotons).
(Schematic of Krakatoa
before the 1883 explosion)
Volume of Material Ejected
by the Volcanic Explosion
The amount of ejected
material from the eruption of Krakatoa into the atmosphere is
estimated to have been about 21 cubic km (appr. 11 cubic miles)
 What was left of Krakatoa after
the Explosion
When Krakatoa erupted
in 1883, the entire northern portion of the island was blown
away.
After the explosions
and the collapse of unsupported remnants into the newly formed
caldera, only 1/3 of the volcano remained above sea level. What
remained were a few small islands marking the previous cone of
the volcano and some small new islands of steaming pumice and
ash to the north. One of the small islands that were born was
"Anak Krakatau" or Krakatoa's Child which is at present
an extremely active young volcano, which at some point in the
distant future may explode with the same violence as Krakatoa.
(Schematic of what
remained of Krakatoa following the 1883 explosion)
Local and Global
Effects of the August 26,1883 Krakatoa Eruption
Effects in the Immediate
Vicinity
Blast waves cracked
walls and broke windows up to 160 km. away. Vibrations smashed
shop windows as far as 80 miles away. Ships navigating the seas
near Krakatoa reported that in certain areas floating pumice
had formed a layer about 3 meters thick. Other ships, 160 miles
off, reported that their decks were covered with volcanic dust
three days after the end of the eruption.
The dust cloud from
the eruption completely covered the area, and it was dark even
257 miles away from the volcano. Darkness covered the Sunda Straits
from 11 a.m. on the 27th until dawn the next day. This darkness
lasted more than 24 hours at places which were 130 miles away
and 57 hours at places which were 50 miles away. In the immediate
area, total darkness continued for three days.
Rain of Volcanic Ash
and Pumice
 There was a rain of volcanic
ash and pumice from the eruptions. In the nearby islands everything
was buried under a thick layer of ash. Plant and animal life
did not begin to reestablish itself to any degree in these nearby
islands for nearly five years.
Near the volcano huge
masses of pumice from the eruption floated in the sea and were
thick enough to interfere with navigation. Pumice formed large
and thick floating rafts some of which crossed the Indian Ocean
in a 10 month period. Others such rafts of pumice reached Melanesia,
and were still afloat two years after the eruption. Volcanic
ash and such debris from Krakatoa's eruption reached as far west
as the island of Madagascar. Quantities of dust from the eruption
precipitated on the decks of vessels as far as 1,600 miles away.
Ash fell on Singapore, which was 840 km away, and on Cocos Island
(Keeling) 1,155 km to the SW. Similar precipitation of ash occurred
on ships at sea more than 6,000 Km away in a WNW direction.
Krakatoa's Explosion
Heard More than 2,000 Miles Away
Krakatoa's tremendous
explosions were heard throughout the area and beyond, over 1/3rd
of the earth's surface. They were heard as far away as 2,200
miles (3,540 kilometers) away in Australia, and even as far away
as Rodriguez Island which is 2,908 miles (4,653 km) away to the
west-southwest, in the Indian Ocean about 1,000 miles (1,600
km) east of Madagascar. People on Rodrigues Island described
the sounds to be like the distant roar of firing canons. The
sounds continued at intervals of three to four hours during the
night.
Atmospheric Shock Waves
Recorded Throughout the World
Atmospheric pressure
shock waves from the explosions of Krakatoa circled the earth
seven times and were recorded by barographs throughout the world.
Barographic records documented the shock waves from the paroxysmal
explosion of Krakatoa by as many 7 times, as these waves bounced
back and forth between the site of the eruption site and its
antipodes on the earth for 5 days following the explosion.
Upper Atmosphere Effects
Ash from the eruptions
was propelled to a height of 50 miles (80 kilometers) in the
upper atmosphere blocking the sun and plunging the surrounding
region into darkness for two and a half days.
Dust and ash from
the eruption encircled the Earth in 13 days forming a cloud which,
by September 9, 1883, had covered completely the upper atmosphere
along a belt in the equatorial zone. Three months after the eruption
this belt of volcanic dust of fine particles of dust had spread
to higher latitudes causing unusually spectacular red sunsets
and other interesting atmospheric effects. Blue and green suns
were also observed. Breathtaking sunsets were observed during
the winter months of 1884 in both American and Europe. Unusual
sunsets continued for almost 3 years.
Climatic Changes
It has been estimated
that at least 21 cubic Km (appr. 11 cubic mile) was ejected from
the eruption of Krakatoa and that at least 1 cubic mile of the
finer material was blown to a height of about 17 miles (27 Km).
The volcanic dust blown into the upper atmosphere was carried
several times around the earth by air currents. This volcanic
dust veil not only created the spectacular atmospheric effects
described previously but acted also 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 degree Centigrade on the average. Weather
patterns continued to be chaotic for years and there were major
climatological changes which affected the entire globe. Temperatures
did not return to normal until five years later, in 1888.
Eruptions of Krakatoa
Prior to 1883
Violent volcanic activity
has been known to exist in this region of Indonesia since early
historic ages. In about 416 A.D., according to ancient Javanese
scriptures, a great eruption" of Krakatau (Krakatoa) must
have taken place. It was this violent early eruption that formed
the three islands of Rakata, Panjang, and Sertung and created
a 4-mile (7-km) wide caldera.The islands of Krakatau, Verlaten,
and Lang are remnants of this volcano.
The earliest recorded
eruption of Krakatoa was a moderate one between May 1680 and
November 1681. This eruption destroyed all of the lush vegetation
on the island. Large quantities of rock pumice and ash fell into
the sea.
Subsequent and Recent
Eruptions of Krakatoa
As reported previously,
prior to the 1883 eruption, Krakatoa was an island made of three
volcanoes and at least one older caldera. The eruption of 1883
destroyed most of of the island, leaving only a remnant.
 (Recent photo of Anak Krakatau)
For the next few years,
what used to be Krakatoa was relatively quiet until, on January
25,1925, a small volcanic cone broke through the water in the
caldera of old Krakatoa. Krakatoa not only was not dead but had
given birth. The new volcanic island was named Anak Krakatau
or Child of Krakatoa. In 1927, occasional weak eruptions of this
small volcano began. In later years, the small eruptions became
more frequent gradually building up this new island volcano to
a much larger size.
in December of 1959,
Anak Krakatau became very active. The renewed activity attracted
a great deal of attention. In January of 1960, a team of scientists
visited Anak Krakatau to study this renewed activity. They reported
that Anak Krakatau had grown to a minimum diameter of about one
mile and was 545 ft. tall. They reported that the crater on the
south side of the island was 2,000 ft. in diameter and contained
a growing cinder cone which was 300 ft. in diameter and 150 ft.
high. This new cinder cone had formed in about a month, since
the resumption of activity. The scientists observed that the
explosive eruption were of the Vulcanian-type and, at the time,
they were occurring at intervals ranging from 1/2 to 10 minute
. They reported that the new explosive eruptions included pyroclasts
ranging in size from fine ash to boulders and that the largest
explosions produced turbulent clouds of ash that rose 4,000 ft.
above the volcanic vent. This renewed activity of Anak Krakatau
lasted for almost four years, ending in 1963.
Since 1963, according
to reports, Anak Krakatau had at least nine episodes of activity
most lasting less than one year. The volcano's activity continued
into the 1990's. As of the writing of this report, the most recent
episode of eruption began in March of 1994 and continued to March
of 1995. This activity was very similar to the 1959-1963 eruptions.
The 1883 Eruption of
Krakatoa was not the Largest Known in Recorded History
Although large and
catastrophic, the 1883 eruption of Krakatoa was not the largest
known in recorded history. The explosion of the volcano of Santorin
(Thera) which occurred in the Aegean Sea in in the fifteenth
century BC, although assigned also a VEI of 6, was at least six
and one half times greater than that of Krakatoa. Also the volcanic
explosion of Mount Vesuvius in 79 A.D was greater than that of
Krakatoa.
 Future Great Eruptions of Anak Krakatau, the
Child of Krakatoa
Undoubtedly the eruptions
will continue and Anak Krakatau, the Child of Krakatoa will keep
on growing in size. Undoubtedly, at some time in the future,
perhaps a few hundred years from now, a large explosion similar
to that of 1883 can be expected. It is only a question of time.
(Photo of Anak Krakatau
at the present time)
SEE ALSO
REFERENCES
IIDA, K., D.C. Cox,
and Pararas--Carayannis, George, 1967.
Preliminary Catalog
of Tsunamis Occurring in the Pacific Ocean. Data Report No. 5. Honolulu: Hawaii Inst.Geophys.Aug.
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Pararas-Carayannis,
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Pararas-Carayannis,
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Pararas-Carayannis,
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ADDITIONAL BIBLIOGRAPHY
- In Chronological Order
Anon., 1883, On
the Tsunami of Aug. 27, 1883,
Daily Bulletin, Honolulu, Aug. 29, 1883.
Fuchs, C. W. C. 1884
Report on the volcanic
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Verbeck, R. D. M.,1884. Krakatoa
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6, HIG-67-25, Univ. of Hawaii, 27 pp.
Sea Frontiers, 1971 "Krakatoa-The
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R.J., and Moser, P.H., 1993, The
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Krakatau Eruption (Geological
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Bulletin of the Global
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p.
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