Sand
People think tsunamis are only made of water but they have a few pieces of sand in there too. There's actually more sand in the ocean than most people think. And tsunamis can't just have water and sharks in them. A few grains of sand will always slip in.
さ, しゃ
すな, よなげる
None
You already learnt the reading for 砂, the other kanji for sand. It should be easy to remember this one too, since it's also さ!