In what experts call "Flash Flood Alley," the terrain reacts quickly to rainfall steep slopes, rocky ground, and narrow riverbeds leave little time for warning.

Rain rushing to the Guadalupe took it from a depth of less than 8 feet to 37.5 feet, a deluge with as much volume as an aircraft carrier over five minutes.

Survivors have described the floods along the Guadalupe River as a “pitch black wall of death” and said they received no emergency warnings.