Jumping and sliding
Jumping oftens result in injury and is the leading cause of slot canyon injuries in Zion National Park. But, jumping and sliding can be extremely fun and may even be the primary draw for some canyons. This page documents considerations for safer jumps and slides.
There is no universal style for sliding/jumping, but in general it is recommended to jump with loose legs, stiff back, and compressed torso (mummy position) and looking forward or up (not down). The loose legs will flex in case of any impact on hidden ledges or rocks, the compressed torso will protect ribs, the stiff back will protect vertebrae, while looking up will prevent face splash or broken jaws. This body position is best taken a split second before the impact with the water for jumps, while for sliding it is best taken and kept throughout the slide. It is rare to be injured by a bad pose doing jumps under 20 ft (6 m), but minor pose mistakes can have serious consequences in jumps 50 ft (15 m) and over. In general, slides are more dangerous than jumps because minor pose mistakes can have unpredictable consequences on the trajectory.
It is recommended to lock off all carabiners before a jump/slide since the impact may cause them to open and fall to the bottom of the pool. Any other hanging objects like cameras, knifes, etc. should also be secured before a jump/slide to avoid hitting the jumper by the impact or becoming lost.
Never ever jump in whitewater! Even if the person in front of you jumped fine, there might be hidden obstacles there that you can crash on. Waterfalls tend to accumulate rocks and debris under the whitewater areas but are usually deepest in the center of the pool.
The first person to jump is the one that takes most of the risk. It's a safe practice, especially if you don't know the canyon and water is not clear, to send a person rappelling down first to check with goggles (or by taking pictures with an underwater camera) that there are no rocks or hidden ledges in the landing area.
Some short jumps are shallow but have sandy bottoms, so it may be safe to jump with legs high and landing on your butt (or bottom of the pack when wearing a pack).
For high jump, anything 30 ft (9 m) or above, it is recommended to jump without the pack to avoid squeezing your body or breaking some strap with the impact. Some people prefer to always jump with a pack (they sink much deeper without) and loosening the waist buckle seems to solve the issue. For very high jump, 50 ft (15 m), taking off the helmet is also recommended.
These are the jumps where a minor mistake may bring disastrous consequences. Run and jump to clear ledges, aiming into small areas, back flips, matrix jumps, etc. are fun to watch but are not for everyone.