A huge flood from Towada caldera in Japan was studied by looking at the Oirase River. Evidence like hanging valleys, boulder bars, and a big fan of sediment showed that a massive flood happened between 15 and 12 thousand years ago. The flood came from the caldera lake and released over 6 cubic kilometers of water at a very high speed. This flood formed the Sanbongi fan, which was previously thought to be made by normal river activity, but it was actually from this catastrophic event.