Mary Bagley, LiveScience Contributor
The eruption of Krakatoa in August 1883 was one of the most deadly
volcanic eruptions of modern history. It is estimated that more than
36,000 people died. Many died as a result of thermal injury from the
blasts and many more were victims of the tsunamis that followed the
collapse of the volcano into the caldera below sea level.
The island of Krakatau (Krakatoa) is in the Sunda Strait between Java
and Sumatra. It is part of the Indonesian Island Arc. Volcanic activity
is due to subduction of the Indo-Australian tectonic plate as it moves
northward towards mainland Asia. The island is about 3 miles wide and
5.5 miles long (9 by 5 kilometers). Before the historic eruption, it
had three linked volcanic peaks: Perboewatan, the northernmost and most
active; Danan in the middle; and the largest, Rakata, forming the
southern end of the island. Krakatau and the two nearby islands, Lang
and Verlatan, are remnants of a previous large eruption that left an
undersea caldera between them.
In May 1883, the captain of the Elizabeth, a German warship, reported
seeing clouds of ash above Krakatau. He estimated them to be more than 6
miles (9.6 km) high. For the next two months, commercial vessels and
chartered sightseeing boats frequented the strait and reported
thundering noises and incandescent clouds. People on nearby islands held
festivals celebrating the natural fireworks that lit the night sky.
Celebration would come to a tragic halt on Aug. 27.
At 12:53 p.m. on Sunday the 26th, the initial blast of the eruption
sent a cloud of gas and debris an estimated 15 miles (24 km) into the
air above Perboewatan. It is thought that debris from the earlier
eruptive activity must have plugged the neck of the cone, allowing
pressure to build in the magma chamber. On the morning of the 27th, four
tremendous explosions, heard as far away as Perth, Australia, some
2,800 miles (4,500 km) distant, plunged both Perboewatan and Danan into
the caldera below the sea.
The initial explosion ruptured the magma chamber and allowed sea water
to contact the hot lava. The result is known as a phreatomagmatic event.
The water flash-boiled, creating a cushion of superheated steam that
carried the pyroclastic flows up to 25 miles (40 km) at speeds in excess
of 62 mph (100 kph). The eruption has been assigned a rating of 6 on
the Volcanic Explosion Index and is estimated to have had the explosive
force of 200 megatons of TNT. (For purposes of comparison, the bomb that
devastated Hiroshima had a force of 20 kilotons. The Mount St. Helens explosion of 1980 had a VEI of 5.)
Tephra and hot volcanic gases overcame many of the victims in western
Java and Sumatra, but thousands more were killed by the devastating tsunami.
The wall of water, nearly 120 feet tall, was created by the volcanoes’
collapse into the sea. It completely overwhelmed small nearby islands.
Inhabitants of the coastal towns on Java and Sumatra fled toward higher
ground, fighting their neighbors for toeholds on the cliffs. The
steamship Berouw was carried nearly a mile inland on Sumatra; all 28
crewmembers were killed. Another ship, the Loudon, had been anchored
nearby. The ship's captain Lindemann succeeded in turning its bow to
face the wave and the ship was able to ride over the crest. Looking
back, the crew and passengers saw that nothing was left of the pretty
town where they had been anchored.
The explosions hurled an estimated 11 cubic miles (45 cubic km) of
debris into the atmosphere darkening skies up to 275 miles (442 km) from
the volcano.
In the immediate vicinity, the dawn did not return for three days.
Barographs around the globe documented that the shock waves in the
atmosphere circled the planet at least seven times. Within 13 days, a
layer of sulfur dioxide and other gases began to filter the amount of
sunlight able to reach Earth. The atmospheric effects made for
spectacular sunsets all over Europe and the United States. Average
global temperatures were up to 1.2 degrees cooler for the next five
years.
Mount Tambora & the year without a summer
While justifiably rated as one of the most destructive volcanic
eruptions of modern times, Krakatoa was not the largest eruption in the
recent history of Indonesia. That “honor” belongs to the eruption of
Mount Tambora on April 10, 1815.
Tambora is the only eruption in modern history to rate a VEI of 7. Global temperatures were an average of five degrees cooler
because of this eruption; even in the United States, 1816 was known as
the “year without a summer.” Crops failed worldwide, and in Europe and
the United States an unexpected outcome was the invention of the bicycle
as horses became too expensive to feed.
The Child of Krakatoa
In 1927, some fishermen were startled as a column of steam and debris
began spewing from the collapsed caldera. Krakatoa had awakened after 44
years of calm. Within weeks, the rim of a new cone appeared above sea
level. Within a year, it grew into a small island, which was named Anak
Krakatoa, or Child of Krakatoa. Anak Krakatoa has continued to erupt
periodically, although mildly.
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| Child of Krakatoa, deadlier than its mother |
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