Years ago a geologist friend of mine was driving with an older experienced geologist far up a Middle East wadi (also called an arroyo or wash in the American southwest). They both heard far off thunder in the nearby mountains at which point the experienced geologist stopped the Jeep and turned to my friend and said, grab your gear and we’re going to climb out of here, now! My friend thought the guy was crazy, but did as he was told. A short time later he watched from the top of the wadi as their Jeep was carried away by a wall of water.