Complex sentence: They are used on hard snow (neve) and ice to provide additional traction and allow very stechniques of alpine skiing and mountaineering to ascend and descend a mountain is a form of the sport by itself, called ski mountaineering.
Split into simpler sentences: They are used on hard snow (neve) and ice to provide additional traction and allow very steep ascents and descents. Combining the techniques of alpine skiing and mountaineering to ascend and descend a mountain is a form of the sport by itself, called ski mountaineering.