Flash floods happen when heavy rains unleash more water than the ground can absorb, causing that water to pile up and flow to low-lying areas

At least 70 people have died and many children are missing in the Texas Hill Country after catastrophic flooding that left officials struggling to explain whether they did enough to warn people of the fast-rising waters.

Hundreds of residents, campers and visitors were plucked to safety after the Guadalupe River rapidly swelled in Texas Hill Country with little warning.