THESE are the waves that I was taught to call ‘tidal waves.’ In reality, they are seismic waves, caused by some movement of the Earth, such as earthquakes or landslides.
Out in the ocean they travel deep in the water. It’s only when they reach shallow water that they start to rise up. The Japanese word ‘tsunami’ means ‘harbor wave’ because fishermen out to sea wouldn’t notice them. It seemed like the waves just appeared in the shallow harbor.
Tsunamis aren’t necessarily large. Any water wave that is caused by a seismic event is a tsunami. So the can be a few inches to several meters high. But that doesn’t mean that all of the water will come in one giant wave. Also, a little known fact is that a tsunami may start by all of the water at the beach rusing AWAY from shore. Remember that a wave has two parts – a crest that rises above the water level and a trough that is below. If the trough arrives first, the water will rush out to sea. If you ever see this happening, run to high ground immediately. A British school girl who knew saved 100 lives.
In this video of the Boxing Day tsunami, you can see several things. It starts with a fairly large wave. Then, if you look carefully, you can see the water recede. There is a single large wave, followed by more waves as the water just keeps coming.
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