Tsunamis are a uniquely devastating natural disaster, something all the more noteworthy given how simple they are. Caused by earthquakes deep under the sea, the water transfers the energy across vast distances – sometimes, if the quake is strong enough, across entire oceans – in the form of giant waves. The danger posed by tsunamis to coastal areas have been understood since coastal areas were first settled, and they figure deep into the histories of countries that have long dealt with them, often construed as the anger of the gods.
These days, we have some better understandings of tsunamis, and with that understanding comes ways to protect ourselves from them – specifically, technology. Let us show you how the world protects people from tsunamis.
You Can Hear the Ocean’s Roar
As we’ve said, tsunamis are caused by earthquakes. How does an earthquake happen? Well, as you might remember from your grade school science classes, the earth moves – slowly, but it moves. The thing is, rocks in the earth’s crust (that’s the part you live on) don’t like to move; they’re heavy and jagged, and get caught and stuck on each other, and sometimes, they get so stuck that they can’t move anymore. But the earth underneath it doesn’t stop just because the rocks are being difficult. It keeps moving; it pushes and pushes until, finally, the rocks can’t take it anymore and they violently shake themselves apart until they end up where they’re supposed to be.
What makes things interesting is when the earthquakes happen underwater. Water conforms to the shape that holds it, and certain earthquakes can suddenly shift the ocean floor in quite the dramatic fashion. When this happens, the water above moves with the seabed; we call this displacement. The water will then carry the energy of that movement, because that’s what water does, creating massive waves that keep going until they either dissipate or hit dry land – usually the latter.
There are three general rules that experts look for in terms of tsunami generation. Firstly – was the earthquake under land, or was it under water? If it was under land, no need to worry. Well, you’d still need to worry, just not about giant waves.
Second – what was the magnitude of the earthquake? Earthquakes are not measured linearly: the magnitude scale is logarithmic. In English, that means a magnitude 7 earthquake is exponentially more powerful than a magnitude 6. In terms of a tsunami, an earthquake that was under a magnitude of 8 is generally less likely to cause a tsunami, while above 8 is generally considered more likely.
Third and finally – what type of earthquake was it? Earthquakes happen on fault lines, and what type of fault line it is determines the strength and severity of the earthquake. Tsunamis are, at the most basic level, a displacement of the water, and that displacement is usually created by one type of earthquake – a convergent fault, where the earthquake causes one side of the fault line to rise suddenly, displacing the water above it.
To be clear, these are not ironclad rules. Strike-slip earthquakes below magnitude 8 have formed tsunamis before. How? Well, one 2018 earthquake in Indonesia caused part of the sea floor to fail, and a huge amount of material was displaced, which in turn displaced the water, which caused a tsunami. Even if they were must-have requirements, it’s to the misfortune of beach-lovers everywhere that it’s relatively easy to get a bingo with all three, because A) earthquakes happen underwater all the time, because there’s tons of water on earth, B) those earthquakes tend to be extremely powerful, and C) that’s because a significant number of the fault lines underwater are enormous reverse faults, not strike-slips.
So, that’s tsunamis, earthquakes, and water all broken down for you. Now that you understand tsunamis, you can understand how to spot for them, and how experts work to keep you from being killed by them.
Used to Sing on the Mountains
Before today’s technological capabilities, tsunami warnings were based on, for the most part, guessing. A tsunami travels, depending on conditions, between 500 and 1000 kilometers an hour, or 0.14 and 0.28 kilometers a second. The seismic waves of the earthquakes that cause them, however, travel much, much faster – typically about 14,000 kilometers an hour, or around 4 kilometers a second. Since the seismic waves can be detected far earlier than the actual waves, that provided the basis for the early warning signal.
The problems with this approach are obvious, given that there’s not a huge amount of information to go off of just from seismic waves. Second, if the earthquake happens just off shore – like, for example, Japan in 2011 – then that isn’t a lot of time to alert people to the possible danger. Thankfully, today, we have something a little more sophisticated, in the form of tsunami early warning networks. Let’s break them down, starting with America’s. That’s right, the United States has a tsunami early warning network. Did you know that?
America’s network, called DART for “Deep-ocean Assessment and Reporting of Tsunamis”, is situated in the Pacific Ocean, because tsunamis don’t really happen in the Atlantic. That’s because the Atlantic fault is a divergent fault, as in the plates are moving away from each other, which produces fewer earthquakes and not barely, if any, tsunamis. The ideas for an early warning network were first floated in the 20th century, following the catastrophe that was the 1960 Valdivia Earthquake in Chile.
The Valdivia quake was the most powerful earthquake in recorded history, and it produced a tsunami so powerful that it crossed the entire Pacific Ocean. On its merry way across the seas, the tsunami slammed into Hawaii, killing 61 people in the town of Hilo. America decided it would be best if their primary naval base in the Pacific wasn’t so vulnerable to, well, the ocean, and so they designed a system to provide warnings of potential waves.
The first part of the network consists of large, durable buoys, combined with pressure sensors anchored to the ocean floor. These combination sensors are deployed at strategic locations all around the Pacific, measuring wave heights and water pressure while monitoring for any suspicious changes in either. When such changes are measured, they are transmitted to a satellite listening in, because satellites are absolute game-changers in terms of weather observation.
That satellite then transfers the data to a computer, where a bunch of experts and algorithms crunch the numbers and make the determination whether a tsunami warning must be issued or not. If they believe there’s a wave coming, evacuations are ordered, and everyone has to get to higher ground.
That’s how the system works to detect a tsunami, but that’s only half the job. Of equal importance is getting the warning out to the people in the tsunami’s path, and that’s done in a myriad of different ways. Warnings are delivered via text, email, radio, even inlaid messages on television screens. Much of this is automated, ensuring that people everywhere can be warned. And it’s a good thing, too, because it most definitely saves thousands of lives when it counts.
But the Mountains Washed Away
Let’s shift from America to the other side of the Pacific, now. Japan is in one of the worst locations in the entire world for tsunamis. Right off the coast is a convergent fault, where one plate slipped under another. These are by far the worst fault lines for powerful earthquakes, and it proved that some ten years ago.
On March 11, 2011, at 2:46 in the afternoon, a magnitude 9.1 earthquake struck off the east coast of Japan, on this exact fault line. This earthquake lasted all of six minutes, which doesn’t sound that long, but in earthquake terms is an eternity. The initial earthquake was devastating enough, damaging buildings and causing liquefaction of the soil, but the worst part was yet to come. On the sea floor, the quake caused an upthrust of 6 to 8 meters, along a seabed 180 kilometers wide, causing an enormous tsunami.
Thankfully, Japan has a robust system similar to America’s, possibly even more so since they have sea walls and more to protect against water surges. Warnings were sent out, evacuations were ordered, and many people made it to safety. But the scale of the tsunami overwhelmed things; the waves were high enough to top over the sea walls, spilling into populated areas and reaching several miles inland. Hundreds of designated evacuation sites were, tragically, washed away. Most waves reached heights of several meters, with some reports that the waves reached up to 40 meters high in places. And, in the most well known disaster of the event, the Fukushima Daiichi nuclear power plant suffered a meltdown directly caused by the tsunami.
As a result of this disaster, nearly 20,000 people lost their lives. But considering the fact that this was the fourth-most powerful earthquake in recorded history, as well as one of the most powerful tsunamis in history, the fact that the damage wasn’t far worse is a testament to how these systems save lives when it counts.
Take, for example, another infamous tsunami in Asia. In 2004, a magnitude 9.3 earthquake occurred off the coast of the island of Sumatra, in Indonesia, producing a tsunami with waves up to 30 meters high in some places. In this disaster, eleven times as many people from 14 separate countries lost their lives as in the Japan earthquake, as they lacked the same early warning systems that might have warned people to head to higher ground – a tragedy, and a good reason to invest in more of these systems in places where they’re needed. And, relatively speaking, these systems are dirt cheap to run, compared to some of the other things governments are known to splurge on. Like tanks, or missiles. Hell, America only built theirs because Hawaii is a naval base. It’s always the military, isn’t it?