What Causes a Tsunami?
A tsunami is a very large, fast-moving wave — or series of waves — usually caused when the seafloor suddenly moves and pushes a huge amount of ocean water upward. Most tsunamis begin with an undersea earthquake: the Earth's crust is made of giant tectonic plates that slowly push against each other, and when stuck plates suddenly slip, the seabed jolts up and lifts the water above it into a bulge.
That bulge of water cannot stay still, so it spreads out across the ocean in all directions, racing through deep water as fast as a jet plane. In the open sea the wave is low and easy to miss, but as it nears the coast it slows down and the water piles up — so the wave grows much taller before it reaches the shore.
Learners come away understanding the four-step chain (earthquake → seafloor lifts → wave races out → wave grows near shore), why tsunamis differ from ordinary wind waves, and the natural warning signs, such as the sea suddenly pulling far back from the beach, that mean it is time to move to high ground.
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A giant wave!🌊 What Causes a Tsunami? A tsunami is a very large, powerful wave (or set of waves) that can race across the whole ocean and crash onto land. It is not made by wind like normal beach waves. Something has to push a huge amount of seawater all at once. Let's find out what! 🔎 Tap Next to begin your adventure.
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The seafloor movesThe seafloor can move Earth's surface is made of giant slabs of rock called tectonic plates. They fit together like puzzle pieces — and they slowly push against each other under the sea. Plate A → ← Plate B deep ocean water The plates get stuck and squeeze, building up energy — like bending a ruler more and more. 🔧
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Earthquake!Step 1: An undersea earthquake When the stuck plates suddenly slip, the seafloor jolts up. That sudden jump is an earthquake under the ocean — the most common cause of a tsunami. 👆 Tap the yellow fault line The plates are stuck and squeezing… give them a tap! Reset the plates
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Water lifts upStep 2: A mountain of water When the seafloor jumps up, it shoves the water above it upward too. This makes a giant bulge of water on the ocean surface. 💧 Drag the slider to push the seafloor up and watch the water rise. Push it all the way up! ⬆️
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The wave races outStep 3: The wave races across the sea That bulge of water can't stay still — it spreads out in all directions as fast as a jet plane. ✈️ In deep water the wave is low, so ships barely feel it. ocean floor ▶ Send the wave! Press the button to launch the wave across the ocean. Speed in deep water can be over 700 km/h — about as fast as a plane!
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It grows near shoreStep 4: It grows tall near the shore As the wave reaches shallow water near the coast, it slows down and the water piles up — so the wave grows much taller before it hits land. land Quick check — why does the wave get taller near the beach? More wind blows Shallow water piles it up The moon pulls it Pick the answer you think is right.
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Order the stepsBuild the tsunami story You learned the 4 steps! Drag the cards into the right order — from first to last. 🧩 Drag a card up or down to reorder it. Check my order
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Warning signsNature's warning signs If you are ever at a beach, these clues can warn you a tsunami may be coming. Tap each card to reveal what to do. 🛟 🌊 The sea suddenly pulls far back The water drains away and shows the seabed. This is a big warning — move to high ground at once! 🤜 You feel the ground shake A strong or long earthquake near the coast can mean a tsunami. Get away from the shore. 📢 You hear a siren or roar Listen to warnings and a loud ocean roar. Follow adults and run to higher, safer land. Tap the cards to learn the safe action.
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You did it!🏆 You're a tsunami expert! Here's the whole story in 4 steps: 1. Plates under the sea suddenly slip → an earthquake 🤜 2. The seafloor jumps up and lifts a bulge of water 💧 3. The wave races across the ocean super fast ✈️ 4. In shallow water it grows tall and hits land 🌊 💡 Other things can cause tsunamis too — undersea volcanoes and big landslides — anything that pushes a lot of water at once! Great job learning how tsunamis form. Stay curious and stay safe! 🌟
Frequently asked questions
- What causes a tsunami?
- Most tsunamis are caused by undersea earthquakes, when tectonic plates suddenly slip and the seafloor jolts upward. That sudden movement lifts the water above it, creating a giant wave that spreads across the ocean. Underwater landslides and volcanic eruptions can cause them too.
- How is a tsunami different from a normal ocean wave?
- Normal waves are made by wind blowing across the surface, so they only stir the top of the water. A tsunami is caused by the whole column of water being pushed, which is why it carries enormous energy and can flood far inland.
- Why does a tsunami grow taller near the shore?
- In deep water the wave is low and travels very fast. As it reaches shallow water near the coast it slows down, and the water behind it piles up — so the wave grows much taller before it hits land.
- What are the warning signs of a tsunami?
- A strong sign is the sea suddenly pulling far back and exposing the seabed, which can happen before the wave arrives. Feeling a strong earthquake near the coast or hearing an official warning are also signals to move quickly to higher ground.
- How fast does a tsunami travel?
- In deep ocean a tsunami can race as fast as a jet plane — around 700 to 800 kilometres per hour. It slows down a lot as it nears the shore, but by then the water is piling up into a tall, powerful wave.
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