Krakatau was seen before the eruption as a small group of islands with the main part towering high above the others in the ocean between the islands of Java and Sumatra.
The main part of Krakatau stood 6,000 feet above sea level before the eruption; afterward it was below sea level.
In the course of the nineteenth century, Indonesia was struck by two of the most powerful volcanic eruptions it had experienced in the past 10,000 years—Tambora in 1815, in the eastern part of the country, and Krakatau in 1883, farther west between Java and Sumatra. Krakatau had one tenth of Tambora’s power but, nevertheless. was sufficiently destructive to profoundly affect places all over the world. Following tremors and minor explosions during the previous night there was one massive outburst of pyroclastic material that rose more than six miles into the upper atmosphere on the morning of the twenty-seventh and at the same time swept across Indonesia, darkening the sky for as far as one could see. The explosion was followed by several tsunamis ranging in height from 40 to 120 feet. Most of the 36,000 who died were victims of the tsunami.
The Krakatau Islands in the Sunda Strait were the above sea level portions of a single volcano that had erupted more than once over the previous million years. Just before its last phase of activity, many centuries before 1883, Krakatau was a mountain that stood 6,000 feet above sea level. When it erupted in 1883 the entire top of the mountain and much of the portion below sea level disappeared and in their place was a huge four-mile-wide crater, known as a caldera. The caldera was mostly below sea level and all that remained visible of Krakatau after the event in 1883 were the four Krakatau Islands, composed of the higher parts of the caldera. At the time of the 1883 eruption, because the eruption originated below sea level and was so massive, the noises of pyroclastic material mixing with water were the most powerful and long lasting experiences of all who witnessed the event. For thousands of miles from Sunda Strait, in places as far away as Australia, the sounds of explosions were heard, and in countries all over the world the atmospheric shock caused by the eruption were registered in their barometers.
Some estimate of the power of the explosion on August 27 can be seen in reports from the time. The place we now know as Indonesia was a European colonial territory in 1883, mainly a Dutch possession and to a lesser extent a British one. A Dutch warship was close to the site at the time of the eruption. As a result, the ship was carried inland for more than a mile and was left there at an elevation of thirty feet above sea level. Extensive damage was done both on land and in the sea. Towns on both sides of the Sunda Strait were completely destroyed; blocks of coral, some as heavy as 600 tons, were torn away from their locations and left on shore; and more than 5,000 boats were sunk. In Australia, four hours after the eruption, a thousand-foot-high tsunami reached almost one mile inland. On the eastern coast of India, in Calcutta, three hundred riverboats were sunk by the tsunami and, still further away at the southern tip of Africa and in the North Island of New Zealand, there were some minor repercussions from this powerful wave of water from Indonesia.
The volume of material that was ejected from Krakatau on August 27 was not understood for many years, not until extensive measurements were taken in and around the Krakatau Islands about one hundred years later. Altogether six cubic miles of materials of different kinds had been thrown out by the eruption and most of that material came back to earth or sea in areas quite close to their source. So heavy was the deposit on the north side that two new islands were formed just below sea level. Coastlines were extended on both sides of Sunda Strait and the ocean around Krakatau was shallower as a result of the deposits. All of these events together gave rise to the two events that were vividly remembered by the people who lived there at the time: the explosive noises of magma and rocks at temperatures of more than 700 degrees entering water, and the tsunamis that were created by the huge displacement of water. The caldera that remained had a diameter of four miles and it was more than two hundred feet below sea level.
Fortunately for us today, detailed records of the events of 1883 were sent back to Europe soon after the eruption by the Dutch and British colonial authorities in Indonesia. Alexander Cameron, the British Consul in Batavia, now the city of Jakarta, wrote a letter to the British Prime Minister, William Gladstone, five days after the volcanic eruption. In the letter, Cameron identified what had happened as one of the greatest calamities of the century. Uppermost in his report were two things: the loud noises that were identical to artillery shells exploding, and the darkness that covered the area around him. He described the latter as a thick cloud of grey ashes that gradually reduced light from twilight conditions to total darkness by midday as the cloud moved eastward. Cameron’s report went on to describe the tsunamis that followed the eruption and affected the neighboring shores of Java and Sumatra, stressing their height and speed. Details of the damage caused and the numbers of lives lost were still unknown as his report was being written because all forms of communication had been interrupted.
Others also recorded their observations. A representative of Lloyd’s of London Insurance Company who was based in Batavia reported to his head office in London that all methods of communication, including roads, had been destroyed, and that the principal peak in the Krakatau Islands— which was almost 3,000 feet high—was no longer there. Other observations came from a harbor pilot whose home was in Anjer on the shore of Java and whose work was to guide ships through the Sunda Strait. The pilot was walking on the beach near his home on the afternoon of August 27 because hot volcanic fragments had been dropping from the sky all day and he was afraid that they would set his home on fire if the thatch on the roof were to be ignited. As he stood on the beach he saw a dark, black object moving toward the shore, something he had never seen before in his many years on the ocean. As the object approached he could see that it was a high wall of water. This was the first of several tsunamis that would, over the following twelve hours, cause the deaths of almost all of the 36,000 who lost their lives.
The deadly tsunamis made the Krakatau eruption different from other events of this kind elsewhere in the world. Approximately 10 percent of the world’s peoples live close to volcanic sites that are either active now or potentially active in the lifetime of those living nearby. Volcanic eruptions occur somewhere in the world every year yet, over the past two centuries during which there are records of close to a hundred tsunamis that were created by volcanic eruptions, not one of them was responsible for as many deaths as were caused by Krakatau’s tsunamis. The more than 150 villages in Java and Sumatra in which people were killed were not the only places destroyed by these tsunamis. Numerous small boats were sunk near shore and those in them drowned as telegraph cables were severed, and all kinds of docking and other shore installations were swept out to sea. A number of larger ships that were some distance from Sunda Strait when the eruption occurred were not affected in any way as they were still in deep water.
As soon as the scale of the disaster became known, corrective steps were taken to minimize additional damage. Warships were stationed on both north and south entrances to the Sunda Strait to stop all approaching ships. This was normally a very busy shipping area so, until the nature and extent of the changes that occurred below sea level were known, the Strait had become an unsafe waterway. On land, the damage affected both human and animal life. Agriculture, the main livelihood of almost all of the people, was suddenly and completely stopped because of the deep layer of ash everywhere. Fodder for animals was unavailable so emergency food supplies had to be found for them. Fruit and palm trees constituted a major source of wealth for the native people and they depended for food on other crops that had been destroyed. The loss of coffee and tea plantations created additional concerns among the colonial officers. These plantations were the sources of profits for the European nations concerned and the main reason for their presence in that area.