A slot canyon is a long, narrow, deep and tortuous channel or drainageway with sheer rock walls that are typically eroded into either sandstone or other sedimentary rock. A slot canyon has depth-to-width ratios that typically exceed 10:1 over most of its length and can approach 100:1. The term is especially used in the semiarid western United States, including the Colorado Plateau region. Slot canyons are subject to flash flooding and commonly contain unique ecological communities that are distinct from the adjacent, drier uplands. Some slot canyons can measure less than across at the top but drop more than to the floor of the canyon. Many slot canyons are formed in sandstone and limestone rock, although slot canyons in other rock types such as granite and basalt are possible. Even in sandstone and limestone, only a very small number of streams will form slot canyons due to a combination of the particular characteristics of the rock and regional rainfall.
The largest known area of slot canyons in Australia is in the Blue Mountains, west of Sydney. They occur in a narrow band of sandstone that runs roughly from east to west, and about from south to north. The majority of these canyons are in the Wollemi Wilderness, and are difficult to access. A small number are regularly visited by canyoners on weekends in summer. The Grand Canyon, near Blackheath, has a tourist track along its rim, but requires abseiling or swimming to visit fully. Sandstone slot canyons can also be found in a few more remote parts of Australia, including Karijini National Park and the Bungle Bungles in Purnululu National Park, both in Western Australia, and Carnarvon Gorge in Queensland. , Utah
Local as well as distant storms can cause dangerous flash flooding in slot canyons, and hikers should not enter them if there is any sign of rain in the surrounding area. In many slot canyons, it can be miles before a safe exit or rescue is possible. On August 12, 1997, eleven tourists, including seven from France, one from the United Kingdom, one from Sweden and two from the United States, were killed in Lower Antelope Canyon by a flash flood. Very little rain fell at the site that day, but an earlier thunderstorm had dumped a large amount of water into the canyon basin, seven miles upstream. The lone survivor of the flood was tour guide Francisco "Poncho" Quintana, who had prior swift-water training. At the time, the ladder system consisted of amateur-built wood ladders that were swept away by the flash flood. Today, ladder systems have been bolted in place, and deployable cargo nets are installed at the top of the canyon. A NOAA Weather Radio from the National Weather Service and an alarm horn are stationed at the fee booth.
