The history of Krakatau
As you might have known by now, Anak Krakatau (meaning “child of Krakatau” in Malay) erupted yesterday at 10:35 p.m. (local time) in Indonesia. This eruption is believed to be bigger than its last one in December 2018 with plumes up to 15 km in the atmosphere.
This volcano is one of the most appreciated in the geoscientific community given the history of its parent volcano, Krakatau. Sometimes we forget how powerful nature is and I, and probably most of you, feel that 2020 is making sure we remember that. This said, in this story, I am trying to show you why Krakatau is so respected and what I believe might happen in the future.
After approximately 200 years of inactivity, Krakatau erupted in August 26th of 1883 and approximately 70% of its caldera collapsed. The explosion was so monstrous that it led to the deaths of 36,000+ people, mostly attributed to the tsunamis it caused. Up to date, it is known as the 2nd eruption worldwide with the highest number of fatalities. The first, also in Indonesia, is from the Mount Tambora 1815 with 71–250+ thousand deaths.
The Krakatau eruption was not the result of a single eruption but of the simultaneous eruption of three volcanoes that shared the same magma chamber in the Krakatau Island.
The 1883 main eruption took place during the 26th and 27th of August and minor eruptions continued for about a year. The rocks from the main eruption reached up to about 27 km. People from other countries, and even other continents, were able to hear the eruption. It could be heard up to 5,000 km away. The noise caused by this eruption is the largest sound ever recorded (310 decibels)!!
Anyone within a 16 km radius became deaf (and dead by the pressure of the sound). The human threshold for pain is about 120 decibels. This explosion was more than twice that!
According to experts, the final blast of the sound wave was 10,000 times more powerful than the Hiroshima atomic bomb. As a reference, the eruption of Mount St. Helens in 1980 was only 500 times as powerful.
The tsunamis occasioned by the eruption reached up to 40 m high and some of them reached South America after crossing the Indian and Pacific oceans. It also reached the English channel (separates the UK from France).
Some of these tsunamis managed to transport blocks of corals of about 600 tonnes. That’s the equivalent of about 86 adult African elephants.
Apart from 25 cubic meters of ash launched to the sky, Krakatau released large amounts of sulphur dioxide (SO2) aerosol particles from its 20 million tons of sulphur. SO2 is a toxic, greenhouse gas that can be converted into sulphuric acid when interacting with the sun and leads to acid rain. This poisonous gas significantly affects climate, resulting in cooler temperatures (up to 1.2°C drop for Krakatau 1883) and the deaths of both fauna and flora.
Why is the cooling of the atmosphere a big deal? Well, remember about the eruption that killed more people so far (Mount Tambora 1815)? The main cause of death was famine. For this eruption, it is also described as “the year without a summer”. The colder temperatures had a tremendous impact on food production in the Northern Hemisphere and led to starvation — the principal cause of death of Mount Tambora 1815.
The aerosol released into the atmosphere originated outlandish colours in the skies. For about 13 days, the sun presented blue and green colours and three months after, it resulted in the vivid red sunset that is so mentioned in the literature of this eruption. Peculiarities in the atmosphere continued for three years after the eruption. Additionally, the lower temperatures persisted for longer (up to a century) in the oceans. This is believed to have influenced the mean sea level.
A fun speculation about this eruption is that it is thought that the sky in the painting “The Scream” (1893) by Edvard Munch was inspired by colours caused by the eruption.
OK. We get it. The Krakatau eruption in 1883 is a historical eruption. But why are we so terrified of its child? Well, while Karakatau had a magma chamber of around 16 km its child has one of 70 km. Hence, if an eruption like the one in 1883 happens again, it has the potential of being considerably more catastrophic. However, Anak Krakatau is far from reaching the size of its maker. Back in 1883, Krakatau had a height of about 6 km. Nowadays, its child has 110 m since its previous most recent eruption in December 22nd 2018. Up to that time, Anak Krakatau had about 324 m above sea level and like its parent volcano, its collapse originated a tsunami, taking the life of +400 people.
At the moment, the internet lacks reports about the most recent eruption of Anak Krakatau. Hence, there is no updated information about its actual current size.
Experts claim that volcanic predictions are improving alongside technologies. However, fully accurate predictions of unusual eruptions seem unlikely. Exactly because of the unusual part.
Eruption styles can alternate in the same volcano. It can be an explosive eruption (like that of Krakatau 1883 and Mount St. Helens 1980) or an explosive eruption where lava steadily flows out of a volcano onto the ground (like the ones often seen in Hawaii). The higher the repose time between eruptions, the more likely the eruption to be explosive as more pressure accumulated over time. Based on this concept, Anak Krakatau seems unlikely to be what its parent once was given its most recent eruptions in December 2018 and the one that occurred last night on March 10th 2020. Additionally, its reduced and smaller size as that of its parent, suggests that if an eruption like the one that happened in 1883 ever happens again it will not take place so soon.
