It’s a killer club song by DVBBS & Borgeous and it’s coming to a Pacific neighbourhood near you to totally ruin your day.
Tsunamis are big waves… the result of a monumental displacement of water that usually takes place at depth somewhere on the ocean floor, although they can also be caused in large lakes and by seismic events occurring at or near the Earth’s surface. The result is a colossal series of waves that only the most baked of surfers would attempt to tackle. The damage is potentially staggering should these waves make landfall and they frequently do.
Makin’ Waves: A How To Guide
As it was mentioned, tsunamis are most often caused by events that have the energy to displace enough water to give the coastlines of the adjacent continents a salt-water enema. What kind of events might these be?
- Earthquakes, the result of a sudden and violent wrenching of Earth’s foundations, can kick the water up and around its epicentre into violent protest.
- Fat celebrities jumping off their gazillion dollar luxury yachts.
- Landslides can send many tonnes of rock and debris crashing into water, generating large waves that can wipe out beaches, forests and any and all human habitation.
- Iceberg calving does the same as landslides, except, instead of earth and rock, it sends mammoth-sized chunks of ice and snow (and perhaps the occasional cryogenically preserved mammoth) careening into the ocean.
- Volcanic eruptions can do both: they can cause incredible landslides of debris into the ocean or a lake and they can cause tremors and earthquakes violent enough to generate tsunamis.
And then there are meteorite strikes that can cause the kind of giant waves portrayed in end-of-the-world movies The Day After Tomorrow and Deep Impact. Even the detonation of nuclear bombs (refer to the totes adorbs film Finding Nemo) can cause billions of litres of previously peaceful water to relocate to your previously peaceful neighbourhood.
Mother Nature Can Be A Real Jerk
Yes, she can. You see, tsunamis – natural disasters in their own right – are typically conceived by natural disasters. As if an earthquake wasn’t enough to rattle your nerves, here comes a solid wall of water and debris to thoroughly spoil your day. This makes them the coarse salt in the wound of the earthquake stricken city – as the Pacific coastline of Japan tragically experienced in March 2011 – and they add insult to injury to anyone who has managed to claw their way through one natural disaster only to encounter another.
Tsunami means “Harbour Wave” in Japanese and the etymology (“word origin” for the vocabulary handicapped) is brilliant…
Japanese fishermen would climb into their creaky little fishing boats and spend the day out on the swell catching fish as fishermen in fishing boats do. Without noticing anything unusual at all, they’d return to the harbour with their soon-to-be sushi only to find their entire village looking particularly soggy and sorry for itself. And so, tsunamis became known as “Harbour Waves” because they didn’t seem to happen anywhere else.
But, how had something as conspicuous as a giant wave escaped their notice? Surely, the wall of water that is a tsunami would have flung the fishermen and their creaky little fishing boats into an abyssal wave trough before crashing ashore?
The answer would be “not necessarily” and here’s why…
Tsunamis are ocean waves, which means that they travel in a waveform and are governed by the same physical parameters and laws. They have wavelength (λ), which is the distance between the trough and the crest of the wave (refer to graph below); and amplitude (a), the distance from the ocean’s resting point to top of the crest.
In addition to having a wavelength and amplitude, ocean waves travel at a certain speed (ν) and with a certain amount of energy (E). People who study physical oceanography make use of all kinds of fancy looking equations to calculate these various parameters given one thing or another. I used to be very well-versed in these equations, since I majored in ocean and atmospheric science back at university. Since those distant book-bound days, however, an abundance of beer, travel and floozies has done its damnedest to erase my memory of these equations and replace them with sweeter recollections. So, I won’t subject you or myself to any math. Rather, I will explain in concept how physical parameters such as energy and wave speed affect wave size, which is something you’re going to WANT to know if your day on the beach takes an unexpected turn for the disastrous.
Photo Credit: Asian Tsunami Video
Water may travel in waves on the open sea, but each wave is in turn composed of hoards of molecules. So while we see ocean waves as a surface oscillation (an up and then down motion of the water) beneath the surface, the composite water molecules are tracing quite different paths. Water molecules in a wave travel in great ellipses, or circles. The molecules closest to the water’s surface have the most fun on the merry-go-round, which you can see in the diagram below, while those at the bottom, nearest to the ocean floor are seriously considering asking for a refund.
Photo Credit: The COMET Program
When a wave is far out at sea where the ocean floor lies many thousands of metres away from the surface, these particle motions are hidden beneath the water and are felt at the surface as a swell. Regular ocean waves or “wind waves” with a garden-variety wavelength of 30 to 40 metres (100 to 130 ft.) are experienced as the kind of rolling up-down motion that can turn you green around the gills if you have a delicate constitution.
Tsunamis, on the other hand, have such a large wavelength that for hundreds of kilometres the water would almost seem to go still as you ride up the side of a very long, yet shallow swell, which belies the presence of the roiling monster passing beneath your very feet. Out at sea, thankfully, you’re none the wiser and also totally safe. On shore, however, things are about to get super soggy.
As a wave travels towards land, the sea bottom rises to meet the continental shelf and then the actual shore. The shallower water slows down or decreases the velocity of the incoming waves. What doesn’t change is the amount of energy the wave is carrying. Think about it: energy IS speed. The faster you run, the more energy you burn. By comparison, relinquishing your hung-over self to the sweet oblivion of your couch requires hardly any energy at all.
Unlike your body, however, waves travelling towards the shore may slow down as they breach shallower depths, but the amount of energy contained by their infinite composite particles remains the same. It’s like running a marathon even though you’re facedown in your couch. Oh look! A quarter!
What does this all mean? Well, if a wave isn’t spending all that energy on travelling fast and yet its energy remains the same when it slows down, where the hell does it all go?
The answer is UP!
So, as a wave approaches the shore, it slows down and compensates by increasing in height. It then becomes visible above the surface of the ocean as rolling, tumbling water… the kind that stringy haired, gnarly Californians like to surf. Wave shoaling essentially explains this process. It’s how those great undulating swells you experience out on the open ocean turn into breaking waves on the shore.
As tsunamis hit shallower water, the seafloor rears up to become dry land and the entire monstrous size of the wave is revealed. It’s owing to the vast wavelengths (and small amplitudes) of these giant waves that they go by completely unnoticed on the open ocean by those Japanese fishermen. All that they would have felt was a slight sea swell, which would be virtually indistinguishable from any of the other swells they had been sitting on all day long. However, the up-to-200km wavelength of the tsunami and its arrival in shallower waters results in the sudden and eerie recess of the sea – like an anomalous low tide – only to bring it crashing back in a surge of super “high tide” that’s so swift and violent, beach goers have only seconds to plan their exit strategies. If there are palm trees nearby, make sure you pick a sturdy one.
You might be there awhile.
Tsunami Statistics (Say That Three Times Fast)
The December 2004 Indian Ocean tsunami that famously struck a number of Thailand’s popular resort towns was generated by a 9.2 magnitude earthquake and killed more than 230,000 people in 14 countries bordering the ocean. Over two million people were negatively affected by this tsunami with the greatest number of deaths being recorded in Indonesia (165,708). The estimated cost of the damage done to countries from Indonesia, Thailand and Myanmar to Sri-Lanka, Kenya and Somalia was $15 billion according to the Disaster Prevention Organization.
The March 2011 Pacific Ocean tsunami that struck Tokyo, Japan, was caused by a 9.0 magnitude earthquake – the largest to have affected Japan on record. The tsunami that made landfall on the 11th of the month reached over 9 metres (30 ft.) in height and caused $300 billion worth of material damage. It also claimed the lives of 15,884 people, according to CNN.com, which is not hard to believe when you take a look at some of the spectacular images to have been published after this disaster.
Class Dismissed: Your Take-Home Message
Tsunamis are big waves caused by the voluminous displacement of water via earthquakes, meteor strikes, iceberg calving, nuclear explosion, landslides, volcanic eruptions and Kirstie Alley at the beach during the nadir of her yo-yo dieting. Tsunamis are one cataclysmic event born from another and for this reason, they are devastating and yet deceptive, because we only know about them when they make landfall.
Owing to their unpredictable nature, they are (surprise) hard to predict and not all tsunami warnings culminate in a tsunami. Likewise, there could be no warning at all and you could find your pacific island holiday rudely interrupted. As with all natural disasters, however, they serve as needed reminders that we are by no means the most powerful force at work on this planet, nor will we ever be.