Hard frozen snow is called nivi. . Over time, the nivi becomes more dense. Eventually, when airtight, it becomes ice. There is soft ice, rotten ice, serac or glacier ice, rime ice, hoarfrost, firnspiegel , hard ice, water ice, gully ice, brittle ice, green ice and blue ice, black ice, verglas and live ice. But there is more to it.
Ice climbing is an inherently dangerous activity.
Only proper training and a thorough understanding of the equipment can reduce the danger. Winter climbing can be even more dangerous than summer rock-climbing. With everyone roped together, for instance, leader falls on ice are frequently more serious than falls on rock. And in ice climbing, everyone is wielding sharp tools, which can be deadly in a fall. Then there are the mental mistakes.