Mystery of the Megaflood (2005)

The Channeled Scablands in Washington state defied conventional explanations for their formation for decades. Little by little evidence mounted for an old theory that was rejected by the scientific establishment. It involved glaciers, volcanoes, a relatively minor river and a prodigious amount of water. Originally aired as an episide of NOVA.

Unfortunately the movie Mystery of the Megaflood is not yet available on HBO Max.