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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.

The 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. 🔧

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!

Step 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! ⬆️

Step 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
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!

Step 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?

Pick the answer you think is right.

Build 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.

Nature'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'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! 🌟