Before evacuating their rental cabin on the edge of Yellowstone National Park, the Manning family watched a nearby house plunge from the riverbank into the raging, flood-swollen waters.

¡°The earth off the bank was coming off in sheets,¡± said Parker Manning, who had traveled from Terre Haute, Indiana, to Yellowstone with his family for a summer vacation.

¡°It was crazy when the house, when the building, finally hit the water,¡± Manning said. ¡°It was floating down the river like a boat.¡±