Why does the ocean recede prior to a tsunami? Where does the water go?
In: Planetary Science
Into the wave
Do an experiment: go to your bed and pick up the middle of your blanket. What happens to the edges? They *recede*, towards the “wave” you’ve made
Imagine you hold a bed sheet at the one end with both hands. You wave it up and down to replicate the way an ocean works. The higher you make your waves you will notice the shorter the sheet will appear until your hands touch the ground and the sheet may overshoot the pillows.
Plug your sink and fill it half way with water. The amount of water doesn’t change from now on. Then place your hand on the water surface and slowly move it up and down.
You’re creating waves. The edge of the sink represents the shore line and you’ll see the water going up and down. Because the volume of water is constant, the level in the middle of the sink has to rise when it sinks at the shore line.
No imagine you’d be able to do one big up and down movement with your hand and the water would follow. This would represent an underwater earthquake. While all the Water follows your hand upwards, the level on the shore line has to drop significantly.
Tsunamis can be formed from a convergent earthquake, which then lifts up a column of water, which when it makes landfall becomes a Tsunami. This column is relatively small in the open ocean and gets higher as the sea become shallow, this results in what is known as drawback basically building the massive wave from the surrounding water. https://youtu.be/QcQv3RJjNYQ
Here’s a [gif](https://www.acs.psu.edu/drussell/Demos/waves/Water-v8.gif) of how individual particles move within ocean waves.
Notice as the wave approaches, the yellow dot actually gets pulled back and up into the wave. Tsunamis are so big, they pull all the water off the beach for quite a long ways before the crest of the wave gets to land.
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