Anak Krakatau is an island in the Pacific Ocean approximately 40 kilometres from Java. It has an explosive history and an explosive nature! The original volcano of Krakatau gave birth to Anak Krakatau. What follows is an explanation of the most powerful volcanic eruption in recorded history.

The History of the Islands

In the year 416AD, Krakatau (Krakatoa) was estimated to be 2 kilometres high, with a radius of some 9 kilometres. Its first recorded eruption was during this same year which resulted in the forming of the islands of Rakata, Sertung and Penjang which were approximately 40 kilometres from Java. It is not recorded how high Krakatau became after this date.

Before the eruption in 1883, the Island of Rakata actually had 3 volcanoes. These were Perboewatan, Danan, and Krakatau.

The Eruption

On 20 May 1883 an 11 kilometres high cloud of ash was reported coming from the uninhabited island of Rakata. Krakatau had begun to wake up. This would be the beginning of 2 months of unstable activity coming from the volcano. During this time, many ships travelling near the island reported seeing similar spectacles which were also accompanied by explosions. Nearby islanders celebrated the spectacle, but little did anyone know the ferocity of the explosion that was to happen on 26 August and would continue until 27 August of that year.

At mid-day Krakatau began to erupt, throwing pumices and ash some 25 kilometres into the sky. So forceful were the explosions, the sound carried as far as Australia. It is impossible to comprehend the force that Krakatau emitted, but to give you an idea of the destructive forces; the volcano blew itself apart, taking the other two volcanoes with it. Only one third of the island of Rakata survived the explosion. The rest of the island then fell 300 metres below sea level.

The cataclysmic Events that followed

The initial blast formed a cloud of volcanic ash and rock that rose 25 kilometres above the island. A few hours later, the cloud widened dramatically to the northeast and rose even higher to around 36 kilometres high, and entered the earth’s stratosphere. Frightened, the coastal communities of western Sumatra, western Java, and other islands close by began to panic. A few hours later, these villages would be devastated by tsunamis.

The Tsunamis

The final blast from Krakatau happened on the following day, 27 August 1883. This blast caused the island to collapse and sent the giant waves, some up to 40 metres in height, across the Sunda Straits. Most of the islands that were closest to Krakatau were completely submerged below the tsunami. No life survived from these islands, which were also stripped bare of vegetation. Some 80 kilometres away, the Thousand Islands were submerged by 2 metres of water. The villagers only saved themselves by climbing up into the trees to get clear of the water.

A ship called the Loudon was anchored in Lampong Bay near the village of Telok Betong. The captain of the ship spotted the tsunami coming broadside to the ship. With skill and fear Captain Lindermann managed to turn the ship head on into the oncoming wave just in time. Had the ship been side on to the wave, it would certainly have capsized, killing all those on board.

For many months after the eruption, the Sunda Straits were clogged with thick pumice banks, which often held fifty or more bodies. To this day¹ it is unsure how many people were killed by the tsunami, although Dutch authorities there at the time calculated the death toll at some 36,417. Nearly 90 per cent of this death toll was attributed to the tsunami.

So strong were the tsunami waves, they were even felt in the seas around Great Britain.

Pyroclastic flows and fallout

If 90 percent of the death toll happened due to the tsunamis, then 10 percent of the death toll, some 4,500 deaths, happened because of Pyroclastic ² flows and falling debris. To give you an idea of the total amount of ash and debris thrown into the air, Krakatau generated some 20 cubic kilometres, which is more than 20 times that of Mount St Helens which erupted in 1980.

The Sunda Straits were congested with so much debris that it appeared to be solid ground, stopping relief ships reaching coastal communities for weeks. Over the coming months, storms and high-tides would scatter the debris. Ships thousands of kilometres from Krakatau reported this floating debris for months after the eruption. One such accumulation floated until it reached the coast of South Africa in September of the following year.

The Pyroclastic flow travelled 40 kilometres over water to reach Sumatra. Approximately 2000 bodies were found with severe burns. The thought is that as the flow travelled over the water, the water turned to steam with the heat of the flow allowing the flow to travel further than it normally would.

Atmospheric problems

Fine particles from the eruption entered the stratosphere before spreading out along the equatorial belt in just two weeks. These particles stayed in the atmosphere for years whilst spreading further north and south before eventually dispersing.

Sulphur dioxide gas within the particles mixed with water to create sulphuric acid. The resulting acidic water and dust created a shield which reflected enough of the suns rays to cause a global drop in temperatures of several degrees. The same vapour also created spectacular effects over 70% of the earth’s surface. For several years after the eruption, halos around the sun and moon could be seen, together with exotic colours in the morning and evening sky.

So rich and vibrant were colours that many times were the fire service called out in New York City. The glow of the evening sky making it look like a catastrophic fire was taking place.

Barometers monitoring the air pressures at the time of the explosion picked up on the pressure waves generated by the eruption. In some cases they were picked up 7 times as the shock waves bounced around the earth.

The Child of Krakatau

A group of Javanese fisherman were startled by steam and debris belching from the sea where Krakatau once stood. This date was 29 December 1927. This marked the rebirth of Krakatau. Within one month of the activity beginning, the tip of a new volcano appeared from out of the sea. The Anak, or child of, Krakatau had been born. A year later, Anak Krakatau became a small island.

Anak Krakatau has erupted in most years since. Typically, these are rather mild eruptions of basaltic andesine lava flows. Although they present little danger to surrounding islands, the eruptions from Anak Krakatau provide an unvarying token of the dreadfulness of 1883.

Anak Krakatau is now an island that hosts plant and animal life. No mammals have been found on the island, but a huge array of plant and insect life are now inhabitants.