A slot canyon is a long, narrow 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 southwestern United States and particularly the Colorado Plateau. Slot canyons are subject to flash flooding and commonly contain unique ecological communities that are distinct from the adjacent, drier uplands.[1] Some slot canyons can measure less than 1 metre (3 ft) across at the top but drop more than 30 metres (100 ft) 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 (containing over 900) is in the Blue Mountains, west of Sydney. They occur in a narrow band of sandstone that runs roughly 30 kilometres (19 mi) from east to west, and about 100 kilometres (62 mi) from south to north. The majority of these canyons are in the Wollemi Wilderness, and are difficult to access. Many canyons within the Wollemi Wilderness have yet to be explored by humans. A small number are regularly visited by canyoners on weekends in summer with those closest to Katoomba being the most frequently visited. The Grand Canyon, near Blackheath, has a tourist track along its rim, but requires abseiling (rappelling) or swimming to visit fully.
There are a number of slot canyons in Spain, especially in the arid foothills of the Pyrenees, such as on the Balcez river.[3] There is an extensive tourism industry built around canyoning in this region. In Czechia, there is a spectacular slot canyon in the Teplice Mountains[4] called Little Siberia due to the microclimate, which is several degrees colder than the surrounding area. The canyons in Teplice are surrounded by pillar-like rock formations which resemble various animals and were the site where The Chronicles of Narnia[5] were filmed.
Drowning danger
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.[6] In many slot canyons, it can be miles before a safe exit or rescue is possible.
Australia's Blue Mountains in particular have claimed the lives of several often due to flash flooding.[citation needed]
On August 12, 1997, eleven tourists, 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.[7][8] 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.[9]
On July 15, 2021, a Michigan woman died in a flash flood that swept through a slot canyon in Grand Canyon National Park. She was a customer with a commercial rafting group that camped overnight about a quarter of a mile from a slot canyon. Five other people with serious injuries were airlifted from the canyon as a result of the same flash flood.[10]
