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Snow Travel, Snow Conditions and Avalanche Awareness

Dave Endres

2/24/10

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Why Snow?

• “Snow is fundamental to mountaineering”• Many peaks cannot be climbed without climbing

snow and/or ice• Snow can facilitate travel over obstacles (brush,

logs, talus, scree, mud, water, swamps)• Snow can allow a more direct route to objective• Less competition from other humans• More wilderness experience• Traveling is snow is fun

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Skills and Equipment?

• Snow travel requires special skills – Knowledge of snow travel, snow conditions and

avalanches

• Snow travel requires special equipment– Skis, snowshoes, adjustable ski or hiking poles

(snow baskets), gaiters, shovel, avalanche transceivers (beacon), probe, snow saw

– Ice axe, crampons (steep or hard snow)• WTC does not include instruction or use of ice

axes or crampons

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Typical Sierra Snow Climb

• Early spring (April-May)

• Snow mostly consolidated and frozen during night and early morning– Start climbing in dark – Ice axe and crampons required– Final ascent typically by gully, chute or couloir

• Complete climb by noon (while snow is hard and prior to afternoon storms)

• After lunch glissade down softened snow in much less time than was required for the climb

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Snow

• Widely variable surface– Varies with time of year, time of day, weather,

aspect

• Water content of fresh snow (1-30%)– Mountain snow typically 7-10% water– Sierra cement 15-20% water

• Fresh powder can be 90% air

• Degree of consolidation– Snow → Ice is a continuum– Distinction between hard snow and ice is arbitrary

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Types of Snow/Ice

• Density of new-fallen snow increases with higher temperatures

• Types of snow– Rime, hoarfrost form at ground level– Powder snow (snowflake)– Corn snow (granular)– Rotten snow (wet, deep hoar snow)– Meltwater crust (refreezing of wet surface)– Wind slab – Verglas (frozen water on rock)

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Snow Travel

• Trails are not visible– Better navigation skills are required (landform

recognition, map, compass, altimeter, GPS, wands)– Must know enough about snow to select safe and

appropriate route

• Best snow – Stable enough not to avalanche– Supports your weight– Easy step kicking

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Finding Best Snow

• South and West slopes– Consolidate faster after storms and early in spring– Softer in afternoon with sun and warmth

• North and East slopes– Consolidate slower after storms and later in spring– Harder in afternoon because of less sun

• Windward– Wind packed firmer surface

• Leeward– Accumulation of soft, unpacked snow

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Local Variation in Snow

• Shade Vs sun

• Dirty snow is usually harder

• Sun cups (well-consolidated stairs)

• Moats (logs, trees, rocks, slopes, couloirs)

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Time of Day and Weather

• Snow can change throughout day or with weather– Firm snow in morning can avalanche in afternoon– Soft snow can change to hard snow/ice in afternoon

or with approaching cold weather• Without crampons or ice axe, a safe descent may be

impossible

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Routefinding

• Ridges (if not too steep or craggy)– Generally little rockfall or avalanche hazard– Exposed to weather and wind– Cornice hazard

• Cornice is a horizontal accumulation unsupported snow on leeward side of ridge (Sierras storms SW winds)

• Looks like frozen breaking wave• Travel well behind fracture line• Fracture line can be 30’ back from lip• Can collapse from weight of climber or spontaneously• Do not travel on, under or through cornices

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Routefinding (continued)

• Gullies, chutes and couloirs (steep)– Rockfall hazard

• Increases during day with increasing temperature

– Avalanche hazard– Try to be out before warmed by sun– Typically used for final ascent– Keep to sides avoiding fall line– Listen for rockfall– Listen for water and watch for ice

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Climbing in Snow

• Ski pole (ice axe) uphill hand– Primary purpose is to avoid falling– Cane and stake position– Self-belay and self-arrest– Climbing in balance (move pole when uphill foot is

forward)

• Climbing– Rest step– Step-kicking

• Pendulum• Slant slightly into hill• Everyone improves steps (single set of steps)

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Climbing in Snow (continued)

• Climbing– Direct ascent– Diagonal ascent– Traversing– Plunge-stepping descent– Glissading

• Sitting, crouching, standing

– Down-climbing

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Avalanches

• Loose avalanches– New snow (Winter)

• Slab avalanches (most common cause of death)– Buried weak layer between slab layer and bed layer

or ground – Depth hoar or buried surface hoar– Buried graupel (soft hail)– Slab formed by brittle, wind-deposited snow

• Wet slab and slush avalanches (Spring)• Avalanches can occur naturally, but are more

often precipitated by human activity

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Anatomy of an Avalanche

• Release zone– Often start in convex or just below convex portion of

slope

• Avalanche slide path– Avalanche chutes

• Steep, open slopes • Indicator or pioneer species (Aspen)• Horizontal aspens• Trees broken off or scarred on uphill side

• Runout zone (can run up the other side of the valley) (-angle 25 degrees from peak)

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Avalanche Hazard• Slope

– Slopes of 25-50 degrees; most common 35-45 degrees (expert to double black diamond)

– Slopes of greater tan 50-60 degrees slough snow constantly

• Slope Aspect– North-facing slopes consolidate slower; prone to avalanches in

winter– South-facing slopes consolidate quicker; prone to wet snow

avalanches in spring and summer– Windward slopes safer because of less snow and wind

compacted snow– Leeward slopes more dangerous because of accumulation of

loose snow

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Avalanche Hazard (Continued)

• Slope Configuration– Slope surface

• Smooth slopes more dangerous (grass, smooth rock slabs)• Trees and rocks help to anchor snow• Slides less likely to originate in forest, but can run through

– Slope Shape• Convex portion of slope where snow is under tension are

more prone to avalanche than concave slopes

– Snow on straight, open, and moderately steep terrain is most dangerous

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Avalanche Hazard (Continued)

• Snowpack– Slab configuration

• Composition of snowpack– Series of discrete layers and their strength, hardness, hardness,

thickness and depth and distribution of weak layers

• Bonding ability– Bonding of layers– Strong layers – dense; composed of small, round snow grains– Weak layers – less dense; composed of loose or sugary

• Sensitivity to stress– Avalanche when stress exceeds strength– Stresses included rapid precipitation, sudden increase in temperature,

windblown snow, human activity

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Avalanche Hazard (Continued)

• Weather– Precipitation increases avalanche hazard

• 1 inch of snow or more per hour• 12 inches ore more of snow in one day• Rain can weaken bonds between and lubricate layers• Rain adds significant weight

– High winds can increase avalanche danger• Form cornices and slabs• Breaks down snow crystals preventing interlocking bonds• Can break cornices

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Avalanche Hazard (Continued)

• Temperature– Unstable depth hoar or sugar snow promoted by

significant differences between temperature of ground and snow surface

– Unstable surface hoar occurs similar to dew on cool, cloudless, calm nights

– Warm temperature promote consolidation– Rapid prolonged warming weakens snow– Cold temperatures make dense layers stronger, but do

not strength weak layers of new, low-density snow– Snow consolidates faster in Sierras than Rockies

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Testing Snow for Avalanche Danger

• Rutschblock (glide block test)– Test representative slope– Dig at least 3 feet deep or to suspected weak layer– Width of ski, depth of ski pole– Excavate 3 sides; cut backside– Interpretation depends on when block fails (during

excavation, approaching block, standing on block, flexing to jump, jump, repeated jumps, no failure

• Shovel shear test• Snow-pit observation• Ski pole probe

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Avalanche Hazard Checklist

• Uncontrollable– Snowpack (slab configuration, bonding, ability sensitivity)– Weather (precipitation, wind, temperature)

• Controllable– Terrain (slope angle, aspect, configuration)– Human factors (attitude, technical skill, strength/equipment)

• Check historical weather and weather forecast• Check avalanche forecasts• http://www.avalanche-center.org/Bulletins/#California• http://www.esavalanche.org/

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Crossing Questionable Slope

• Put on hat, mittens and warm clothing• Undo ski poles and safety straps from skis and

snowshoes• If route is uphill - proceed straight up hill without

switchbacking• Traversing – proceed one at a time as high on

slope as possible while everyone else listens and watches from a safe place, cross with long smooth strides, one set of footprints, do not fall, minimize exposure, stop in a safe place

• If possible avoid roping up, if not belay from an anchor, belayer does not tie in

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Surviving an Avalanche

• Keep eye on escape paths• If caught, fight to survive, try to get off moving

snow, run uphill, jettison unnecessary gear (skis, ski poles snowshoes), keep pack, hold on to tree or rock, dig ice axe or ski pole into be surface, swim by flailing arms or rolling towards side of slide

• Avoid inhaling snow, as avalanche slows thrust upward, if buried make a breathing space by putting hand or elbow in front of face, breath deeply before snow solidifies, conserve energy and air

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Avalanche Rescue

• Survival depends on being a well-prepared party– Training and practice, conditioning and judgement– Transceiver, shovels, probes– Black Diamond Avalung II, avalanche air bags

• Don’t loose point where victim was last seen • Search will focus on this spot (mark) and

downhill on fall line (look for clothing or gear)• Do not go for help

– 90% survival if located with 15 minutes– 25% survival if located after 90 minutes

• Leader organizes a methodical search

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Searching

• Transceiver search– Coarse search

• Look for partially buried individual, clothing or equipment• Searchers spaced no more than 50 feet apart• Easier to work downhill

– Fine search• Bracket method (identify 6 foot square)• Tangential method (faster, more difficult to learn)

• Pinpoint search– Transceiver and gentle probes (avalanche probes)– Formal probe searches require too much time– If no transceiver, probe most likely spots

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Hazards of Snow Climbing

• Failure to arrest from a fall can result fatal collision with a tree or rock

• Ice axes and crampons are sharp and dangerous tools and must be used with skill– Sucking chest wounds can easily result from contact

with the pick of an ice axe.

• An avalanche can ruin you life

• Snow climbing requires special skills and knowledge– Get professional instruction before participating in

this activity