Flash floods in Texas have killed nearly 90 people, many of them children. Heavy rains fell quickly in the predawn hours Friday in the Texas Hill Country, causing the Guadalupe River to rise 26 feet in just 45 minutes.

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

The very qualities that draw people to the beautiful Texas Hill Country — rolling terrain, limestone formations and lazy rivers — also make the area deadly during heavy rainstorms.