Free solo climbing, also known as free soloing, is a form of free climbing where the climber (the free soloist) foregoes ropes, harnesses and other protective gear while ascending and relies only on his or her physical strength, climbing ability, and psychological fortitude to avoid a fatal fall. Free solo climbing should not be confused with free climbing, in which gear is used for safety in case of a fall, but not to assist the climb. Less risky alternatives to free soloing include bouldering (climbing at heights low enough that a fall would typically be safe) and deep water soloing (climbing where falling would result in harmlessly falling into water).
Reasons for free soloing given by high-profile climbers include the simplicity and speed with which one can climb, a feeling of intense concentration required, and the adrenaline rush. The practice is mostly confined to routes familiar to the climber and whose difficulty lies well within the climber's abilities. However, inherent risks such as loose rocks or sudden change in weather are always present, and some high-profile climbers have been killed this way.
Yosemite climbing program manager and park ranger Mark Fincher said there has been only one confirmed death from free-soloing at the park, that of Derek Hersey, a high-profile free-soloist who died on Sentinel Rock in 1993. The challenge of free soloing single pitch routes is mainly in the mental difficulty for the climber of staying focused on what they are doing. Free soloing is usually not meant to be hard in a physical sense. That said, however, unpredictable weather and rock conditions can create grave hazards for climbers on longer routes. Hersey, though a master of solo climbing's physical and mental demands, is believed to have encountered rain during his fatal solo ascent of the 1000-meter Sentinel Rock.
Some of the driving forces in rock climbing and free soloing from 1900 to today: Paul Preuss, Henry Barber, John Bachar, Derek Hersey, Peter Croft, Alexander Huber, Dan Osman, Dean Potter, Hansjörg Auer, Alain Robert and Michael Reardon.
Remaining close to the ground (typically below 25 ft.) and using protective mats is known as bouldering and is another, safer alternative.