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Addressing questions most ocean visitors have had and offering new ones for our consideration, The Science of Ocean Waves: Ripples, Tsunamis, and Stormy Seas explains in accessible language how waves are formed, how they move, how they become huge and destructive, and how they’re being studied now for clues that will help us plan for the future.
The immense swell of a tsunami can grow up to 100 feet, hitting speeds over 500 mph — a treacherous combination for anyone or anything in its path.
Alex Gendler details the causes of these towering terrors and explains how scientists are seeking to reduce their destruction in the future.
Saved by the wrath of Poseidon
In 479 BC, when Persian soldiers besieged the Greek city of Potidaea, the tide retreated much farther than usual, leaving a convenient invasion route. But this wasn’t a stroke of luck. Before they had crossed halfway, the water returned in a wave higher than anyone had ever seen, drowning the attackers.
The Potiidaens believed they had been saved by the wrath of Poseidon.
But what really saved them was likely the same phenomenon that has destroyed countless others: a tsunami.
Tsunamis are caused by energy originating underwater
Although tsunamis are commonly known as tidal waves, they’re actually unrelated to the tidal activity caused by the gravitational forces of the Sun and Moon. In many ways, tsunamis are just larger versions of regular waves. They have a trough and a crest and consist not of moving water, but the movement of energy through water.
The difference is in where this energy comes from.
For normal ocean waves, it comes from wind. Because this only affects the surface, the waves are limited in size and speed.
But tsunamis are caused by energy originating underwater, from a volcanic eruption, a submarine landslide, or most commonly an earthquake on the ocean floor caused when the tectonic plates of the Earth’s surface slip, releasing a massive amount of energy into the water. This energy travels up to the surface, displacing water and raising it above the normal sea level, but gravity pulls it back down, which makes the energy ripple outwards horizontally. Thus, the tsunami is born, moving at over five hundred miles per hour.
When it’s far from shore, a tsunami can be barely detectable since it moves through the entire depth of the water. But when it reaches shallow water, something called wave shoaling occurs. Because there’s less water to move through, this still massive amount of energy is compressed. The wave’s speed slows down, while its height rises to as much as 100 feet.
Tsunami, ‘Harbor wave’
The word tsunami, Japanese for ‘harbor wave’ comes from the fact that it only seems to appear near the coast.
If the trough of a tsunami reaches shore first, the water will withdraw farther than normal before the wave hits, which can be misleadingly dangerous. A tsunami will not only drown people near the coast, but level buildings and trees for a mile inland or more, especially in low-lying areas.
As if that weren’t enough, the water then retreats, dragging with it the newly created debris, and anything, or anyone, unfortunate enough to be caught in its path.
The 2004 Indian Ocean Tsunami was one of the deadliest natural disasters in history, killing over 200, 000 people throughout South Asia.
So how can we protect ourselves against this destructive force of nature?
People in some areas have attempted to stop tsunamis with sea walls, flood gates, and channels to divert the water. But these are not always effective.
In 2011, a tsunami surpassed the flood wall protecting Japan’s Fukushima Power Plant, causing a nuclear disaster in addition to claiming over 18,000 lives
Many scientists and policy makers are instead focusing on early detection, monitoring underwater pressure and seismic activity, and establishing global communication networks for quickly distributing alerts.
When nature is too powerful to stop, the safest course is to get out of its way.