A serac is a large block or pinnacle of glacial ice, formed where a glacier breaks up over steep or uneven ground. Seracs can topple without warning, making serac fall one of the deadliest objective hazards in mountaineering. Climbers minimize the time they spend beneath them.
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.
Acclimatization is the physiological process by which the body gradually adjusts to the lower oxygen of high altitude — by breathing faster, producing more red blood cells, and other adaptations. Ascending slowly to allow acclimatization is the key to preventing altitude sickness; the body typically needs days to adapt to each major elevation gain.
A flip-flop is a thru-hiking strategy where a hiker completes a long trail out of the usual sequence — for example hiking partway, jumping to the other end, and hiking back to the gap. Flip-flopping helps hikers dodge bad weather, crowds, or seasonal timing windows while still covering the entire trail.
A bear bag is a method of hanging food and scented items in a bag from a tree branch, out of a bear's reach, to protect it overnight. Techniques like the PCT method suspend the bag high and away from the trunk. Bear bags are lighter than canisters but harder to do well, and are banned where canisters are required.
A bear canister is a hard-sided, bear-resistant container that backpackers use to store food, trash, and scented items overnight, keeping them from bears. Required in many wilderness areas, canisters protect both hikers and bears — a bear that gets human food often becomes dangerous and may have to be killed.
Fording is crossing a river or stream on foot where there is no bridge. Hikers face upstream or angle across, unclip the pack hip belt, use trekking poles for stability, and judge depth and current carefully. Swift water is deceptively powerful, making fords one of backpacking's real hazards.
The Yosemite class rating system describes how difficult and exposed terrain is to travel, from Class 1 to Class 5. Class 1 is walking, Class 2-3 is steeper hiking and easy scrambling, Class 4 is exposed scrambling where many use a rope, and Class 5 is technical roped climbing. It helps hikers gauge a route's seriousness.
The alpine zone is the ecological region above treeline, where harsh cold, wind, and short summers allow only low-growing, fragile plants like grasses, sedges, and cushion plants. It offers stunning open terrain but is highly sensitive — hikers stay on rock or trail to avoid trampling vegetation that takes decades to recover.
Slackpacking is hiking a long trail while someone else transports your overnight gear, so you carry only a light day pack between points. Often arranged through hostels or shuttle services, it lets hikers cover trail miles with far less weight, trading some self-sufficiency for comfort and speed.