I witnessed my first flash flood decades ago in the Oman. Fortunately we were camped far enough - just - above the floor of the wadi to be able to simply watch and listen - with a sense of terror. The photo above is from Zion National Park a couple of years ago - torrential rains, devastating flash floods - and the clunking sound of boulders rumbling along the bed. Only a few hours earlier we had been wandering through Antelope Canyon, beautiful but infamous and deadly, with wary eyes on the gathering clouds (see here for an incredible video of the canyon filled by a flash flood in 2013 and here for an image of a relatively minor 2010 flood emerging from the canyon).
Flash floods can occur anywhere, any time - Texas is under a flash flood watch as I write this and Maryland was devastated only a couple of weeks ago. They can come with no warning whatsoever and yet their power is indescribable.
Hence Dana Hunter's recent post - "Instant Peril: Flash Floods (and How to Survive Them)." Wherever your travel plans will be taking you, but particularly if they include arid lands, read this.
If you want a further taste of the staggering power of flash floods when they turn into debris flows (which, more often than not, they do), watch these videos (originally reported on "The Landslide Blog," thanks to Dave Petley).
And never forget Isabelle Eberhardt, the luminous writer (but troubled and enigmatic human being) who drowned in the Sahara.