Tsunami's have a certain tendency to secrete things as they go back out to sea. When they bash themselves onto the land they just throw a bunch of sea water around, but there are only certain things that they'll secrete when they're leaving.

Most tsunami's secrete heat (ひ). It takes a lot of energy for a tsunami to crash onto the land so the water is really really hot, and it has to secrete that heat as it's going back out to sea.