Some people are really afraid of water. Mostly those who don’t know how to swim. And I totally understand, I was like that too, but somehow I my curiosity pushed and I became a swimmer at the age of 9. At 11 I was already very comfortable with water but still if it’s a about large surface such as the Ocean, I do hesitate to jump in without extra protection available. I don’t like very deep waters. I am a very good swimmer, but in the ocean I am too vulnerable so I don’t push for that.
Even if you’re not a wave connoisseur, it’s still worth knowing about shoaling, because it could save your life. On the morning of 26 December 2004, tourists on the island of Phuket in Thailand were walking on the beach when they noticed something odd. The sea was receding fast, exposing usually submerged rocks and leaving boats in the bay stranded. Children watched and wondered, and so did their parents, as a large wave suddenly appeared; they thought they’d never seen anything like it before. But, of course, they had. This was the shoaling of a wave, only this wave was enormous: a tsunami.
As it turns out, just a few hours earlier, in the middle of the Indian Ocean, part of the Earth’s crust had ruptured, causing an earthquake of magnitude 9.0. This is a massive earthquake by any standards. The energy released was estimated to be 10.000 times bigger than that of the atomic bomb dropped on Hiroshima. Nevertheless, being that far out to sea, it didn’t cause much immediate damage or loss of life. But the earthquake didn’t just shear the tectonic plates of the crust – it also raised the sea floor by several metres. This, in turn, displaced approximately 30 cubic kilometres of water. That’s a lot of water – the equivalent of 10 million Olympic swimming pools. And just as moving suddenly in the bath makes the water slosh back and forth, the earthquake set this enormous amount of water into motion.
Waves being waves, they set off across the ocean in all directions. If you’d been looking down from an aircraft at the moment the tsunami began, you probably wouldn’t have been too worried. The waves were spread over such a large distance, and in such deep water, that only a small hump would have been discernible. But you might still have been alarmed by the speed at which they were traveling. Because of the intensity of the earthquake, and the vast amount of energy released over a short period of time, those waves traveled at the speed of a jet aircraft, about 500-900 km/h. As they approached the cost and the shallow water of the Andaman Sea, they slowed down, and got taller. The closer they got, the more the shoaling intensified. Because the waves were hundreds of metres long, the first thing the people on the beach noticed was the water being sucked out to sea. If they had recognized the phenomenon, they would have had about a minute to run to higher ground. But, tragically, most of them didn’t know what was happening – unlike many of the animals near the beach, who seemed to sense something was happening and fled. Those who stayed were hit by the first wave, which was 10 metres high when it reached the shore.
All in all, the tsunami killed 227,898 people along the coastlines of 15 countries. What makes a tsunami so dangerous is not just the vast amount of water it dumps on the coast, but the force that water exerts on everything it meets. One cubic metre of water weighs a tonne, and the tsunami displaced 30 billion cubic metres of water. It ripped apart huts, trees and cars, destroying them and thus creating a river of debris that smashed into everything it met. It swept up tankers and houses, and flung them into bridges and overhead electricity pylons, which collapsed, creating lethal fires.
The people who were pulled into the wave were carried along, bashed, knocked, tumbled and crushed by all this fast flowing debris. This knocked many of them unconscious or injured them in a way that hindered their ability to stay afloat. Just like storm waves, tsunamis come in sets, and as the first wave was pulled back (having reached two kilometres inland in places) by the approach of the second, the currents reversed and pulled the people and debris caught in their path into this new onslaught. Unfortunately, those who were lucky enough to survive this devastation were then faced with any number of challenges in its aftermath, water pollution being one of the most severe. The fresh-water supplies in the areas hit by the tsunami had been poisoned by the destruction of sewers and the infiltration of salt water; the hundreds of thousands of people struck dead by the waves all had to be buried as quickly as possible to prevent the spread of disease and pests; and longer-term infiltration of salt water into the region’ s arable land left it unable to support crops.
But as catastrophic as the 2004 tsunami was, the one in 2011 off the coast of Japan was even more powerful. The tsunami was created by the force of an enormous earthquake – the 4th most powerful in recorded history – with an epicentre in the ocean, 70 kilometres off the shore of Honshu, the largest island in the Japanese archipelago. Shaking was felt on and for 6 minutes, but the worst damage didn’t occur until later, when the resulting tsunami hit the shore, devastating entire towns, and colliding with the Fukushima Daiichi Nuclear Power Plant.
Fukushima Daiichi was built in 1971, and had 6 nuclear fission reactors. Nuclear fission reactors are made up of rods of uranium oxide, which are bundled together inside the reactor core. A reactor emits radiation in the form of very high-energy particles. In a nuclear power plant, most of this energy goes towards heating up water to create steam, which drives turbines, which in turn create electricity. This type of nuclear energy is so powerful that a set of rods of uranium oxide the size of a small car will produce the amount of electricity needed to run a city of a million people for 2 years.
Prior to the 2011 tsunami, the Fukushima plant had 6 of these reactors, all producing power 24 hours a day, 365 days a year, for approximately 5 million people. Japan has a long history of earthquakes; it lies at the boundary between 2 major tectonic plates. The Fukushima plant was built to withstand these earthquakes, and indeed it did. As did Japan’s other 54 nuclear reactors. When the earthquake occurred on 11 March 2011, it didn’t damage the plant at all. However, due to legally mandated safety precautions, 3 of the reactors (1, 2 and 3) all shut themselves down (reactors 4, 5 and 6 were already shut down for refuelling). You can’t just turn nuclear fuel ‘off’. It still gives out heat and radioactivity when the reactors are shut down. They need active cooling to prevent a meltdown of the uranium oxide. During shutdown, this is provided by diesel-fuelled backup generators, which produce electricity to power the pumps that circulate the cooling water.
Ultimately, 13.000 people would die as a result of the 2011 earthquake; but at the time the shaking stopped, and the reactors shut down, 90% of them were still alive. Then, 50 minutes later, a 13-metre tsunami wave traveling at an average speed of 500 km/h hit the power station. The water destroyed the plant’s sea wall defences and flooded the buildings containing the diesel generators that were cooling the nuclear fuel rods. The generators failed, and a second backup system kicked in, powered by a set of electrical batteries. The batteries had the capacity to run the plant’s cooling systems for 24 hours. Under normal circumstances, this would have been enough time either to restore the diesel generators or to obtain more batteries. However, the tsunami, the biggest Japan had encountered in modern times, destroyed anything and everything in its path. The sheer force of the water pulverized whole towns, 45.000 buildings and almost a quarter of a million vehicles, and left a mess of the region’s roads and bridges. The areas where the tsunami hit came to a standstill, making it incredibly difficult to get medical help to the survivors, and impossible to get the backup batteries to the Fukushima plant in time to replace the ones running the cooling systems. 24 hours after the tsunami hit, the batteries died and the temperature inside the reactors started to rise.
When nuclear fuel rods melt, they look a lot like lava, but the liquid is much hotter. Lava comes out of a volcano red hot, typically 1000°C. Liquid uranium oxide nuclear fuel is much more fearsome, a white-hot liquid with a temperature exceeding 3.000°C. It will melt and dissolve pretty much anything it comes in contact with. At Fukushima, it melted its way through the 10 inches of steel that had been containing it, and then continued to eat its way through the concrete floor of at least one of the reactors. But that was just the beginning. The nuclear fuel in the reactor is encased in an alloy made from zirconium. It is incredibly resistant to corrosion, except at high temperatures. At 3.000°C, the zirconium alloys react strongly with water, producing hydrogen gas. It’s estimated that, as a result of the meltdown, 1.000 kilograms of hydrogen gas were produced in each of the plant’s reactors.
On 12 March, the hydrogen gas reacted with the air inside the reactor containment building, creating an explosion that destroyed the complex. Liquids are incredibly hard to contain, and as a result a great deal of the radioactive contamination from these nuclear meltdowns made its way into the area’s water systems, and ultimately the sea. From there it can and does go anywhere and everywhere. This is why the primary concern of all nuclear-waste engineers is preventing water ingress into any of their storage facilities. Yet most nuclear power stations are built near large bodies of water, not because it’s safer, but because it’s cheaper. They need to use the water for cooling: having a large supply readily available makes the plant much more energy and cost-efficient, but, as we saw in Fukushima, when disaster strikes, our water supply is vulnerable to a huge
amount of radioactive waste.
This isn’t just a nuclear issue. Almost all of the world’s major cities are coastal because, historically, trade between countries required ports. But with sea levels rising as a result of global climate change, the impact of tsunamis and hurricanes and storms is going to make these places – and their dense populations – ever more vulnerable. The only way to protect ourselves from this threat is to get to higher ground, or perhaps into the air.