A post in underwater360 does a great job of explaining what happens when you scuba dive in a tsunami. It explains that if you are out at sea at a depth of about 20 meters and 200 meters away form the shore, the effects of a tsunami would be barely noticeable.
Furthermore it is pointed out that the effects of a tsunami can vary between spinning currents, surging water in one direction or another , even up and down. It is these types of extreme underwater movements that make divers vulnerable to many types of dangers as highlighted in the excerpt below.
Those dangers can be fatal, depending on how shallow or deep you are:
If you’re deep, a “washing machine” current can pull you up and down – and if you ascend too quickly, you’re at risk of the decompression sickness
With the water criss-crossing, it’s easy for your group to be broken apart. Disorientated and pulled by the current, you could end up losing your buddy
If you’re too close to powerful tsunami waves, you’re at risk of being dragged inshore onto hard land
Just like in drift diving – only much stronger and faster – there is the risk of crashing into underwater structures, being knocked unconscious or sustaining fatal blows
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