Well, it wouldn’t be the first time since the end of the last glaciation that the ice suddenly gave way. I would have hated to have been down stream when the glacial dam that created Washington’s scablands gave way.
The Washington area badlands are a pretty freaky area of the country- and hard to comprehend the enormity of what must have happened.
My guess is a meteor hitting water, but not sure why it only affected Washington, unless it manages to hit some blocked up huge reservoir of water (but where was THAT stored..???)