Albert Pike Campground Flash Flood: How It Happened

The news that at least 16 people were killed by flash floods overnight at the Albert Pike Campground in Caddo Gap, Arkansas echoes similar tragedies in the region. Last December, one person was killed in similar flooding in Fayetteville, about 185 miles north of the current disaster.

Elsewhere, one of the deadliest rain-related flash floods in U.S. history killed 237 people in Rapid City, S.D. in 1972. In 1889, a flash flood resulting from a broken dam killed more than 2,200 people in Johnstown, Penn.

Flash floods occur within several seconds to several hours of intense rain, often with no warning. They occur whenever the amount of rainfall overwhelms drainage and absorption systems and continues to surge through a low-lying area. Run-off from storm systems further upstream may not reach an area for a few hours, so meteorologists often advise people to remain off the streets for several hours following an intense storm.

Mountainous areas--such as western Arkansas's Ouachita Mountains--are especially susceptible to such flooding, as steep inclines funnel water down into narrow canyons at incredibly fast rates. 30-foot-high waves are common, and can destroy buildings, tear out trees, and cause mud slides. Within seconds, a dry area can be submerged by a roaring torrent.

Flash floods account for the vast majority of flood-related deaths each year. Flooding in general kills more than 100 people and forces some 75,000 Americans from their homes each year.

UPDATE, 9:11 p.m.: This afternoon, Arkansas Gov. Mike Beebe briefly put the death toll at 20 before revising the confirmed fatalities total to 16. More than 40 people are thought to be missing.