Glossary of Avalanche Terms
A terrain feature where an avalanche occurs. Composed of a Starting Zone, Track, and Runout Zone.
An electronic device worn on the body to aide in quickly finding buried avalanche victims. Also called an avalanche beacon, it has the ability to send and receive a 457khz radio signal.
The surface over which a fracture and subsequent avalanche release occurs. Can be either the ground or a snow surface.
When the fracture of a lower snow layer causes an upper layer to fall. Also called a whumpf, this is an obvious sign of instability.
A terrain feature that is rounded inward like the inside of a bowl, i.e. goes from more steep to less steep.
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding and conservative decision making essential. Natural avalanches possible; human triggered avalanches likely. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.
A terrain feature that is curved or rounded like the exterior of a sphere or circle, i.e. goes from less steep to more steep. Convex slopes tend to be less safe than concave slopes.
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A mass of snow deposited by the wind, often overhanging, and usually near a sharp terrain break such as a ridge. Cornices can break off unexpectedly and should be approached with caution.
A steep gully in alpine terrain. In winter, a couloir is usually filled with snow bound by rocks on either side.
Wind blowing across a slope, depositing drifts on the sides of gullies or other terrain features.
The top fracture surface of a slab avalanche. Usually smooth, clean cut, and angled 90 degrees to the bed surface.
In the U.S., a five-category estimation of the avalanche danger: Low, Moderate, Considerable, High and Extreme.
Avalanches that break deeply into old weak layers of snow that formed some time ago.
Large-grained, faceted, cup-shaped crystals near the ground. Depth hoar forms because of large temperature gradients within the snowpack.
Avoid all avalanche terrain. Natural and human triggered avalanches certain. Large to very large avalanches in many areas.
Angular snow with poor bonding created from large temperature gradients within the snowpack.
The physical separation of the slab from the bed surface and surrounding snow during the initiation of a slab avalanche.
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Natural avalanches likely; human triggered avalanches very likely. Large avalanches in many areas; or very large avalanches in specific areas.
When a snowmobiler ascends a slope to the highest point they can reach. Also known as hill climbing.
When all layers of the snowpack are at the same temperature, usually the freezing pointt. Often refers to a snowpack that is wet throughout its depth.
A snowpack stratum differentiated from others by weather, metamorphism, or other processes.
The addition of weight on top of a snowpack, usually from precipitation, wind drifting, or a person.
An avalanche that releases from a point and spreads downhill collecting more snow - different from a slab avalanche. Also called a point-release or sluff.
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human triggered avalanches unlikely. Small avalanches in isolated areas or extreme terrain.
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches unlikely; human triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas.
Weak layers that continue to produce avalanches for several days or weeks after a storm.
Supercooled water droplets that freeze to objects in exposed terrain, forming icy deposits on the windward side. Rime can also form on snowflakes as they fall through the sky, giving them a fuzzy appearence.
Wind eroded snow, which often looks rough like frozen waves. Usually found on windward slopes.
The slow, deformation and densification of snow under the influence of gravity. Not to be confused with collasping
A stability test where a skier or rider rapidly crosses an avalanche starting zone to see if an avalanche initiates. Slope cuts can be dangerous and should only be performed by experienced people on small avalanche paths or test slopes.
Backcountry skiers and some snowboarders ascend slopes using climbing skins attached to the bottom of their skis.
The physical change of snow grains within the snowpack due to differences in temperature and pressure.
The amount of water contained within the snowpack. It can be thought of as the depth of water that would theoretically result if you melted the a column of the snowpack, and corresponds to inches of water precipitation.
A pit dug vertically into the snowpack where snow layering is observed and stability tests may be performed. Also called a snow profile.
The chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human).
A procedure used to estimate the stability of the snowpack, often done in a snowpit. Common tests include the Rutschblock, compression or tap test, cornice drop, and slope cut
When a slab avalanche slides a short distance and breaks down into deeper weak layers forming a stair-step pattern on the bed surface.
Featherly crystals that form on the snow surface during clear and calm conditions - essentially frozen dew. Forms a persistent weak layer once buried.
Terrain in which the consequences of an avalanche are especially hazardous, such as a gully, an abrupt transition, an avalanche path that terminates in trees, a crevasse field or a cliff.
A disturbance that initiates fracture within the weak layer causing an avalanche. In 90 percent of avalanche accidents, the victim or someone in the victims party triggers the avalanche.
When a snowstorm deposits denser snow over less dense snow, creating a slab/weak layer combination.
A snowpack layer with less strength than adjacent layers. Often the layer in the snowpack where an avalanche fractures.
An avalanche caused by snow losing its strength after becoming damp, moist or saturated with water.
A cohesive layer of snow formed when wind deposits snow onto leeward terrain. Wind slabs are often smooth and rounded and sometimes sound hollow.
The upwind side of an obstacle such as a ridge. Usually snow is eroded from windward slopes making them relatively safer.