Icicle in the context of Solidification

Freezing is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point.

For most substances, the melting and freezing points are the same temperature; however, certain substances possess differing solid-liquid transition temperatures. For example, agar displays a hysteresis in its melting point and freezing point. It melts at 85 °C (185 °F) and solidifies from 32 to 40 °C (90 to 104 °F).

Ice climbing is a climbing discipline that involves ascending routes consisting entirely of frozen water. To ascend, the ice climber uses specialist equipment, particularly double ice axes (or the more modern ice tools) and rigid crampons. To protect the route, the ice climber uses steel ice screws that require skill to employ safely and rely on the ice holding firm in any fall. Ice climbing routes can vary significantly by type, and include seasonally frozen waterfalls, high permanently frozen alpine couloirs, and large hanging icicles.

Ice climbing originated as a subdiscipline of alpine climbing, where sections of scalable ice are encountered alongside segments instead necessitating rock or mixed climbing. Ice climbing arose as an independent sport in the 1970s. Modern ice climbing includes a difficulty grading system peaking at WI6 to WI7, as ice tends to hang vertically at its most severe. WI7 is very rare and usually attributed to overhanging ice with serious risk issues (i.e. unstable ice, little protection, and a risk of death). Mixed climbing has pushed the technical difficulty of ice climbing routes by crossing bare rock overhangs and roofs. This can entail dry-tooling, the use of ice tools on bare rock.