In 479 BC, the Persian soldiers laid siege to the Greek city of Potidaea. The tide unusually retreated much farther than usual, providing a seemingly convenient invasion route. However, this was not 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 Potiidaeans 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.
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 500 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 is 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.
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.
Create a simple tsunami simulation using a large tray, water, and a small object to represent land. Push down on one end of the tray to simulate an underwater earthquake and observe how the waves form and move. Discuss how this relates to the formation of tsunamis.
Research a historical tsunami event, such as the 2004 Indian Ocean tsunami or the 2011 Japan tsunami. Create a presentation that includes the causes, effects, and lessons learned from the event. Present your findings to the class.
Develop a tsunami safety plan for your community. Identify safe evacuation routes, emergency supplies, and communication strategies. Create a poster or brochure to share your plan with others.
Write a short story from the perspective of someone experiencing a tsunami. Describe the events leading up to the tsunami, the impact, and the aftermath. Use descriptive language to convey the power and danger of the tsunami.
Design an awareness campaign to educate others about tsunamis. Create posters, social media posts, or a short video explaining what tsunamis are, how they form, and what to do in case of a tsunami warning. Share your campaign with your school or community.
persian – relating to Persia or its people – The Persian Empire was one of the largest empires in history.
greek – relating to Greece, its people, or their language – The Greek civilization made significant contributions to philosophy and mathematics.
potidaea – an ancient Greek city located on the Pallene peninsula of Macedonia – Potidaea was a thriving city-state during ancient times.
tsunami – a long high sea wave caused by an earthquake, submarine landslide, or other disturbance – The devastating tsunami in 2004 claimed thousands of lives in Southeast Asia.
tidal waves – large, powerful ocean waves caused by the gravitational interactions between the Sun, Moon, and Earth – The coastal town was heavily damaged by the impact of tidal waves during the storm.
energy – the capacity to do work, generate power, or cause change – Renewable energy sources such as solar and wind power are becoming increasingly popular.
water – a transparent, odorless, tasteless liquid that forms the seas, lakes, rivers, and rain and is the basis of the fluids of living organisms – Drinking enough water is essential for maintaining good health.
earthquake – a sudden and violent shaking of the ground, often caused by the movement of tectonic plates beneath the Earth’s surface – The earthquake measured 7.2 on the Richter scale and caused widespread destruction.
coast – the part of the land near the sea; the edge of the land – She decided to take a walk along the coast to enjoy the refreshing ocean breeze.
disaster – a sudden event, such as an accident or natural catastrophe, that causes great damage or loss of life – The hurricane resulted in a major disaster, leaving thousands of people homeless.
