What do the Megapon onomatopoia mean?

I know that in japanese they use katakana to describe different sounds, but I can't figure these out, nor what they mean. I think it's クテーbut the exclamation marks would be at the beginning which I think would be weird. Anyway, could anyone please explain to me? Thank you so much.

https://preview.redd.it/9vs7n55tc95g1.jpg?width=2992&format=pjpg&auto=webp&s=a29e9080182307e50d2e3e90655731ccce38292d