Self-arrest is the technique of stopping yourself after a slip or fall on a snow slope by using an ice axe to dig into the snow and halt your slide before you gather dangerous speed. It is one of the most important and practiced mountaineering safety skills, drilled repeatedly because a real arrest happens in seconds.
An ice axe is the fundamental mountaineering tool — a shaft with a pick-and-adze head and a spike at the base — used for balance and support on snow slopes, cutting steps, building anchors, and, crucially, self-arrest to stop a slide. Every snow and glacier mountaineer carries and knows how to use one.
Crampons are metal frames with downward and forward-pointing spikes that strap or clip onto boots to grip snow and ice. They let mountaineers and ice climbers walk and climb on hard, slippery terrain. Designs range from flexible walking crampons to rigid technical models, matched to the boot and the terrain.
Glacier travel is the technique of crossing a glacier safely as a roped team, managing the hazard of hidden crevasses. Climbers travel roped together at set spacing, ready to arrest a fall and perform crevasse rescue, while reading the glacier's surface for sagging snow bridges and other signs of crevasses below.
Crevasse rescue is the set of techniques for extracting a climber who has fallen into a crevasse, using the rope, snow anchors, prusiks or ascenders, and mechanical-advantage hauling systems like the Z-pulley. It is an essential skill for glacier travel, practiced until it's second nature, because a real rescue must be fast and is physically demanding.
A crevasse is a deep crack in a glacier formed as the ice moves over uneven terrain. Crevasses can be tens of metres deep and are often hidden beneath snow bridges, making them one of the principal hazards of glacier travel. Mountaineers rope up and learn crevasse rescue to manage the danger.
The death zone refers to altitudes above about 8,000 metres (26,000 ft), where the oxygen is too thin to sustain human life for long. The body deteriorates rather than acclimatizes, so climbers use supplemental oxygen and move fast. Prolonged time in the death zone leads to exhaustion, altitude illness, and death.
HACE (high-altitude cerebral edema) is a rare but deadly form of altitude illness in which the brain swells with fluid, causing confusion, loss of coordination, and altered consciousness. It is a medical emergency requiring immediate descent and treatment; without rapid action, HACE can be fatal within hours.
HAPE (high-altitude pulmonary edema) is a severe, life-threatening form of altitude illness in which fluid accumulates in the lungs, causing breathlessness, a cough, and extreme fatigue. It can develop within days of ascending too high too fast, and immediate descent and emergency care are essential — HAPE can be fatal within hours.
Altitude sickness, or acute mountain sickness (AMS), is illness caused by ascending to high altitude faster than the body can acclimatize to the reduced oxygen. Symptoms include headache, nausea, fatigue, and dizziness. It can progress to the life-threatening conditions HAPE and HACE, so the response is to stop ascending and, if it worsens, descend.