Considering the excellent sliding surface that snow affords, the skier might well wonder, "Why doesn't this snow avalanche?" instead of "Will it avalanche?" Any rugged snow terrain demonstrates that the ava­lanche is the rule, not the exception. Almost as soon as snow falls, it slides from the steeper cliffs and rock faces. What kind of ground or rock surface, then, will hold it? Once it is held by the ground, what will hold each suc­ceeding snowfall to the snow layer it falls upon? Indeed, what holds one snow crystal to another? These are basic questions, and there are three more: What precautions should be taken in avalanche territory? What should one do if caught in an avalanche? And what can one do for others who are trapped?

Much of this chapter, which endeavors to answer these questions, will seem unduly technical and dryly scientific. Yet the tragic toll of human life taken every year by snow avalanches makes it necessary that every man who ventures onto steep snow slopes be capable of telling when danger exists. He must be able to say with assur­ance that "this slope is safe," "this slope is unsafe," or "this slope will be safe if we cross it one hour after the sun has left it."

There is no short cut, no easy rule of thumb to de­termine whether a snow slope is in danger of avalanching. Experience alone is not enough. There may be no chance for a second experience. Required is an accurate knowl­edge of the internal structure of snow, why it is some­times packed as hard as concrete, at other times is as fluffy as down, as gritty as sand, as sticky as pie dough, or as slushy as mud. The crystalline structure and texture of snow is in a continual process of change from the time the snow flake is first formed until it either melts or compacts to solid ice. Thorough knowledge of the causes and results of this change underlies an understanding of the causes—and results—of an avalanche.

Snow Texture

Crystalline structure of fresh snow.—There are many forms of snow crystals (see fig. 6), all of which are hexagonal, consisting of plates, prisms, star-shaped de­signs, or a combination of these forms. In general simple crystals are formed when the temperature is low. The range of size is, roughly, from 1-4 mm. in diameter. A snowflake frequently consists of a cluster of interlaced snow crystals. Snow crystals of the simple plate form accumulate loosely compared to the branched type of crystal. The points of the branched crystals interlace and cohere within a mass of new-fallen snow. An avalanche is, therefore, less likely to occur immediately after a snowfall made up of branched crystals. Snow made up of the simpler type of crystals will flow more readily.

Fig. 6. Typical forms of new snow crystals.

Consolidation of crystals.—As soon as snow has fallen a transformation begins. If the temperature is above freezing, the branches of the crystals begin to melt, de­stroying the interlocking bond. Even if the temperature is below freezing, these branches will still, although more slowly, disappear because the vapor pressure of the ice particles, and consequently evaporation, is greatest at the points. This evaporation will take place even though the humidity is such that no net evaporation results, since the difference in vapor pressure will cause ice to evaporate from the points and attach itself to flatter portions of the crystals.

Fig. 7. Crystals of "spring" or corn snow.

The result is a gradual trans­formation from branched or thin-edged snow crystals to larger hexagonal crystals. The smaller crystals in turn tend to consolidate with larger crystals. By this basic process new-fallen snow is converted gradually to the "spring snow," which every skier knows (fig. 7). The rate and manner of change will depend on the weather, but the process is always going on, and accounts for variations in the internal cohesion of the snow. Cohesion is at first reduced by the loss of the interlocking crystal branches, but as the process continues, the large crystals which are finally formed pack more closely, so that the snow settles and cohesion again increases. But when temperature and humidity produce wet crystals, the film of water, acting as a lubricant, reduces internal cohesion.

Effect of wind on texture.—The effect of wind on fallen snow is varied and difficult to predict accurately. The primary effect of a dry wind is evaporation of the snow. A humid, or wet wind nearly always causes packing of the surface snow (assuming that the snow is not already hard-packed), and simultaneously causes erosion (wind-cut snow) and drifting. Wind packing sometimes forms a crust which is well bonded to the underlying snow; however, if there is simultaneous deposition of fresh or drifting snow, a wind slab is apt to form. This is poorly bonded to the underlying snow, and may break up when disturbed, sliding away in blocks. Therefore, wind slabs are likely to be on lee slopes; a wind-cut surface is usu­ally a safe crust and not a slab. Frequently, soft snow under a wind slab will settle unevenly, leaving spaces under the slab. Owing to the lack of continuous support the slab breaks easily under the weight of a skier.

The rate of consolidation to "spring snow" is ap­preciably accelerated by wind. The acceleration is due to the greater rate of evaporation of the branches and edges of the snowflakes. If the wind has a low humidity, there may be a large net evaporation from the snow field, but wind with a high humidity may actually deposit moisture or ice. If the moisture freezes immediately, an icy crust or a hoarfrost is formed, depending on the temperature. If it remains wet it may make the snow very unstable and subject to avalanche until frozen.

In summary, the effect of wind varies considerably, de­pending on whether it is above or below freezing, and has a high or low humidity. If the temperature and humidity are both low, no crust need be expected; if the tempera­ture is low, but the humidity is high, wind crust or wind slab will be formed (or hoarfrost); and if the tempera­ture and humidity are both high, the snow will become quite wet.

Fig. 8. Formation by wind of cornice and snow cushion.

Drifting and erosion.—Wind is of great importance in determining snow conditions. It tends to pack and erode the snow on windward slopes, simultaneously depositing drifted snow on lee slopes. These drifts may become very deep and sometimes have a steep lee side. Since the friction and evaporation during movement of the snow tends to remove the branches from the crystals, the co­hesion of these drifts initially is usually low, and dry-snow avalanches may result if the snow is not wind packed. Wind slabs may be formed, however, if the snow is drifted by humid wind and collects at a point where the wind velocity is reduced, but is not calm.

In traveling over the crest of a ridge, drifting snow frequently forms cornices (see fig. 8). These occur in the calm triangular region between the air current flow­ing over the top of a ridge and the eddy current drawn up the lee side of the ridge by the main current of air. Drifting snow carried by the main current settles, in part, into this comparatively calm region, and builds out the cornice, either by the interlocking of the crystal branches, or by formation of a wind slab. Snow carried past this calm region before dropping out of the main air current falls below the cornice and forms a drift, generally known as a snow cushion.

The formation of a large cornice is favored by a wind­ward slope which is 15-30° and a leeward slope of about 52°. Cornices can be formed, however, with windward slopes from level to about 45°, and with lee slopes from perpendicular to 30° or less.

Cornices are often unstable, their collapse the frequent cause of avalanches. The snow cushion in itself is fre­quently an avalanche hazard. Where possible, routes should be so planned that cornices are avoided. More­over, skiers should bear in mind that a flat and innocent-looking ridge crest may in reality be a cornice that is overhanging several feet and is on the verge of collapse.

Stratification of Snow Deposits

The stability of a given layer of snow depends not only upon its texture and internal cohesion, but also on the cohesion between the snow layer and the underlying surface. For when a vertical section is cut from the top­most surface of the snow to the ground, it is seen that each successive snowfall forms a separate and distinct layer of snow. In general, the lower layers have larger, better consolidated crystals. The difference between the layers is due to the difference in weather during and be­tween successive snowfalls, and to the greater age of lower layers.

Bond between layers.—A new layer will be well bonded to the previous layer if it falls when the previous layer is wet, or if the falling snow itself is somewhat damp. This is particularly true if the temperature falls after the snowfall has commenced, thereby freezing the new snow to the old snow. If, on the other hand, the old snow is-fairly well packed and the temperature is well below freezing, the bond is likely to be very poor until the new layer has also settled. The bond is particularly poor if the new snow falls on crusted snow. The crust may be due to wind, but is even worse if it is due to thawing; and then refreezing to form a smooth icy surface. In other words a layer of loose, unconsolidated snow lying on a smooth crust is apt to avalanche.

Flow of water through strata.—The stratification of snow has further effects during a thaw. If the snow i& melting, or if water is running down through it because of thawing conditions higher up the slope, then one layer of snow may become wet while other layers remain unaffected. In filtering through snow, water tends to saturate a densely compacted layer such as a wind crust, in preference to traveling through a looser snow texture, and it may rise up through the layer from the bottom rather than flowing down from the top. This is because the water motion is governed primarily by capillary at­traction, which tends to make it flow along the crystal surfaces, just as kerosene flows up a lamp wick, or ink into a blotter. Water in a snow layer not only reduces the internal cohesion, but also tends to provide a waterlubricated upper surface over which an overlying snow layer may slide.

If a solid ice crust is present, any water formed above this crust cannot flow down through it, and when the snow above becomes saturated, additional water will, therefore, run down over the surface of the ice crust. This results in a very wet surface on the ice crust pro­viding a particularly well lubricated surface on which the next higher layer of snow may slide.

Thus, where several layers of snow are present, one layer may be wet without the others being wet, and the wet layer is not necessarily the upper layer. It is there­fore not enough merely to know that the upper layer of snow possesses good internal cohesion, since it may be lying either on a loose lower layer or on a lubricated lower ice crust, either of which may permit the upper layer, or several layers, to slide away.

The skier must accordingly consider whether there exists on any suspected slope a lubricating snow layer, either dry or wet, below the surface. Avalanches caused by the yielding of several layers are particularly danger­ous because of the depth of the snow released.

Effect of Slope and Ground Surface

Steepness of slope.—Generally speaking, the steeper the slope, the greater the danger of avalanche. Avalanches are not likely to occur on slopes less than 22°, but can occur on lesser slopes if other conditions are unusually favorable. Much steeper slopes than this are entirely safe if snow texture and snow bondage are good.

Ground surface.—Inequalities in the ground surface, such as rocks, mounds, or terraces, tend to give a firm anchorage to the lowest snow layer, and whenever numer­ous firmly placed rocks are protruding above the snow, the avalanche danger will be negligible. Rounded, down­ward-sloping ledges give little support to snow, but angular, upward-tilted ledges give considerable support. Grass usually forms a poor bond with the lowest snow layer since the grass bends downhill and is matted into a slippery surface. This is sometimes also true of the more flexible types of brush, but shrubs with fairly rigid

stems give a good bondage. Trees growing in a close

wood serve both as a good bondage and as an indication that avalanches have not recently swept through the region. Avalanches can fall, however, from a sparsely wooded slope, and even dense woods are sometimes swept out by avalanches starting above the wood. Water-satu­rated soil is obviously a slippery surface.

It should be borne in mind that the ground surface and vegetation affect only the snow layers into which they protrude. After the ground and vegetation is completely covered and a smooth snow slope is formed, each suc­ceeding snow layer must be bonded to lower layers in order to obtain any support from the original surface.

Contour.—The general contour of the mountainside also affects the bondage of the snow. On a concave slope, the snow in the lower, flatter portion of the slope tends to support the snow higher up, whereas on a convex slope the steepest portion is at the bottom, and it consequently provides less support for the snow on the flatter portion at the top.

The effect of contour is relatively important if the principal cause of an avalanche is a lack of bondage be­tween the sliding layer and the next lower layer, which may be the ground. The snow then slides, to a certain ex­tent as a blanket. The effect of contour is less important when the danger of avalanche is due to lack of internal cohesion within a snow layer so that the snow flows downhill. A wind slab on a convex slope is more likely to be under some initial internal tension than a wind slab on a concave slope. A slab on a convex slope, therefore, should tend to fracture more readily.

Most avalanches fall in chutes or gullies (or couloirs); indeed, in high mountains, these chutes owe their exist­ence primarily to erosion by frequent avalanches. These avalanches are mostly of the flowing type, however, and are frequently started by snow falling off the headwalls. Obviously, then, when a skier crosses an avalanche chute, it is not enough that he merely know the character of the snow in the chute. The imminent danger is in the slopes high above, the structure of which is usually en­tirely different from slopes in the chute.

Avalanche Types

Avalanches may be placed in four classifications: those of ice, dry snow, wet snow, and wind slab. Combinations of several types may occur; for example, an ice ava­lanche may start several layers of snow, both wet and dry, old or new, on their way down a mountainside.

Ice avalanches.—In any precipitous region undergoing heavy glaciation, ice avalanches are frequent, and often of tremendous proportions. Hanging glaciers high on a mountainside will move beyond their support and col­lapse, sweeping everything before them. In the Himalaya, avalanches started in this manner have been known to travel fully a mile across a level valley floor before spend­ing themselves. Where the course of a glacier is less precipitous, a cliff may be entirely covered with ice, being indicated only by the heavily crevassed and chaotic surface of the glacier, known as an icefall. Here the seracs, or pinnacles of ice, often collapse to cause ava­lanches of large proportions.

For the purpose of this chapter, it will be presumed that the skier who travels in terrain that spawns such avalanches will be fully prepared, by study and experi­ence acquired elsewhere, for the problems that will con­front him. But a milder hazard from falling ice is fre­quently encountered in any rugged ski terrain. Water from melting snow will freeze on cliffs during the night, or whenever the temperature is low enough, and will break loose with the first thaw. The breaking loose of large accumulations of ice may cause a snow avalanche on the slopes below. It is usually easy to see where such bombarded areas exist, and to plan a route that avoids them, or to time the trip so the party passes beneath the cliffs when the ice is frozen.

Dry-snow avalanches.—New snow: This is the most frequently encountered avalanche. The primary cause is a loss of internal cohesion soon after a snowfall, owing to evaporation or transformation of the branches of the snow crystals. This eliminates the bond initially provided by the interlacing of these branches, and permits the snow to flow. Avalanches of this type may occur during or soon after a snowfall, wherever the slope is steep enough. If the snow has fallen on a frozen crust, or even on settled snow when the temperature is well below freezing, the likelihood of avalanche is increased since the poor bond may permit slippage as well as flow, and more gradual slopes are apt to avalanche. If the layer of new snow is only a few inches thick, the likelihood and seriousness of an avalanche is slight, but if the fall has been very deep, or has been collected in large drifts, the likelihood of avalanche, and the possible damage from it, is great.

The length of time between the start of a snowfall and danger of avalanche, and the further length of time before the snow will have settled sufficiently to become safe again, depends on the weather conditions and slope ex­posure. If the slope is exposed to sunshine soon after the fall, dry new-snow avalanches may occur within a few hours, and if the sunshine continues, the danger from avalanche will be over within two or three days, and will be greatly reduced after one full day of warm sunshine. If the temperature is very low, however, and if the snow is not exposed to sunshine, the period before avalanches may occur is extended, and it may be two or three weeks before safe conditions are reestablished. Danger from this type of avalanche should therefore be suspected from almost any time during a heavy snowfall until not less than two or three days later, and the length of time that danger should be suspected is governed by the exposure of the slope and the weather conditions known to have existed subsequent to the fall of snow. Generally speak­ing, south and west slopes will avalanche first and become safe again first, whereas north and east slopes, receiving less radiation from the sun, will remain dangerous for a longer period. This period may be affected, however, by wind. Wind may pack the new fall of snow sufficiently to remove the hazard; if the wind is humid, it may form a wind slab, which introduces the hazard of a different type of avalanche; wind may form large snowdrifts which may be hazardous. A humid wind above freezing temperature may make the snow wet and introduce the hazard of a wet avalanche.

Settled snow: This type of avalanche is rare and is only likely to occur when the support of the snow is removed. This may result either from loss of bond with the underlying snow, resulting, for example, from water seepage over an underlying crust, or from loss, perhaps by avalanche, of support derived from snow on the lower part of a very steep slope, the upper portion of which is covered with settled snow.

Wet-snow avalanches.—New snow: A wet new-snow avalanche may occur when the snow becomes damp be­cause of sun, rain, warm humid wind, or high air tem­perature, and may well be expected whenever the snow becomes sticky or sloppy. Here again, the likelihood of an avalanche will depend not only on the wetness of the snow, but also on the gradient and contour of the slope, and the bondage to the underlying snow or ground layer. The extent to which a wet new-snow avalanche will slide as a blanket or roll in huge balls will depend on how wet the snow is. Water in small quantity increases cohesion, but reduces cohesion when present in a large quantity, just as is true with dry, damp, and very wet sand.

Old snow: Wet old-snow avalanches usually fall be­cause the snow has become so heavy from water that its weight cannot be held by internal cohesion or its bond to underlying snow or ground. This type of avalanche usually falls in the same tracks each year. Abnormal ava­lanches may occur in years of heavy snowfall or warm spring. The snow in such an avalanche is wet and slushy, and flows very much like mud.

Wind-slab avalanches.—Wind-slab avalanches may oc­cur at any time after formation of a wind slab, until the slab has settled and is once more bonded to the under­lying snow. The ease with which a slab slides after being broken depends on the character of the underlying snow and the gradient of the slope, and the ease with which it breaks depends on the toughness of the slab, on its thick­ness, on its size, and on the depth of the space between the slab and the underlying snow. The thickness of slabs varies from a few inches to two or three feet. It should be borne in mind that a snow slab may be formed and then covered by a later fall of snow which completely conceals it. The presence of a snow slab which is broken by the weight of a skier as he travels can be detected by the dull thud occasioned by the settling of the slab, and when the slab is not covered, the lines of fracture can be seen to run off some distance from the point of breakage. This extension of the fracture is one of the visible points of distinction between wind slab and wind crust. The effect of breakage of wind crust is quite local, with no tendency to break up the crust to any distance from the point of fracture. Hoarfrost is sometimes formed be­tween a wind slab and the underlying snow. Since the internal cohesion of hoarfrost is very low, this increases the likelihood that the wind slab, lubricated by the hoar­frost, will avalanche after breakage. The avalanche con­sists of large blocks of wind slab, which may subse­quently break up during the fall, and is especially dangerous if the blocks are large. Skiers caught in such avalanches are usually crushed by the blocks.

Detection of Snow Condition

With respect to the methods of determining that ava­lanche conditions exist, no amount of discussion can re­place experience; but the skier can be cautioned to take advantage of certain classes of available information.

The most complete knowledge of snow conditions at a given point can be obtained by cutting a section through the snow from the surface to the ground and examining the texture of the snow in each layer and the firmness of the bond between layers. This method is usually too laborious to be practical, and normally requires the use of a shovel. An approach to such an examination can be obtained, however, by prodding the snow with a pointed stick, such as a ski pole with the basket removed, with a reversed ski pole, or with the heel of a ski. Al­though this does not permit visual examination, it will indicate any hard crust or probable wind slab below the surface within a depth corresponding to the length of the pole. The skier must remember, however, that ski-pole detection will not go far enough to disclose the most dangerous avalanche hazard—that of several feet of sur­face snow avalanching on a deeply buried but poorly bonded underlayer.

Frequently it is desirable to know the probable condi­tion of snow at so distant a point that it cannot be directly examined. This, and the condition of underlying snow which cannot be readily examined, is best learned by study of past weather conditions. Records of weather must be used with caution, as local variations due to slope exposure, wind, and altitude, may make notable difference. Weather reports may serve, however, to a limited extent. For example, if temperatures well below freezing are reported to have prevailed prior to and during a snowfall, there will be a greater danger of ava­lanche following the snowfall than if the temperature is known to have been above freezing prior to and during the first stages of the snowfall, followed by lower tem­peratures during the balance of the storm. Or, if rain or a heavy thaw were followed by a freeze and then by ad­ditional snowfall, an impermeable ice crust would prob­ably have formed, which would provide poor bondage for overlying new snow, and over which water from the thawing snow might collect as a lubricant for a subse­quent avalanche.

The skier on one slope may judge the snow on a near­by slope by considering its relative exposure. Thus, if the slope on which he stands is wet from the sun, or is covered with a sun crust due to wet snow being refrozen, he can probably obtain better skiing conditions by cross­ing to an unexposed north slope, although in this event he must assure himself that the snow there has settled sufficiently to be past a point of danger from new-snow avalanche. Similarly, if the skier knows the direction of the prevailing wind or of the wind which is reported to have existed in the recent past, he can predict where wind crust may have formed and where drifts are likely to be found. He can judge of the probability of wind slab or wind crust if he knows the humidity of the wind which took place.

A thermometer and to a slightly lesser extent a hy­grometer can be of considerable value in determining the changes which are likely to be taking place in snow condition. An experienced mountaineer can determine temperature and humidity fairly well, however, by "feel" and by telltale signs.

Summary of Avalanche Causes

An avalanche occurs whenever the pull of gravity on a snow mass is sufficient to overcome anchorage or internal cohesion. To determine the probability of an avalanche on any suspected slope the skier should consider the fol­lowing factors:

1. Steepness of slope.
   
   
2. Shape of slope.
   
   
3. Anchorage to ground surface and bond between snow layers.
   
   
4. Possible existence of a buried snow slab.
   
   
5. Internal cohesion of visible and buried snow layers.
   
   
6. Recent weather as affecting the last three factors.
   
   
7. Evidence of prior avalanches.
   
   
8. Depth of snow.

Precautions in Avalanche Territory

Safest part of slope.—Careful study of dangerous slopes should always be made, if possible, in conjunction with others. The party should give thought to the time of day and its probable effect upon the chances of an avalanche. It will always be preferable to avoid any slopes which appear to be in danger of avalanche. This is not always possible, however, and some consideration must be given to the least dangerous method of traversing dangerous slopes. In general, a dangerous slope should be crossed as near the top as possible. An exception to this rule, however, must be made when the slope is considerably concave, so that the upper portion is steepest. An excep­tion should also be made when the slope is surmounted by a cornice, since there is the double danger that the cornice may fall, thus starting an avalanche, and that a deeply drifted snow cushion may exist just below the cornice.

The advantage of crossing high is that the skier will then be above most of the sliding mass of snow if an avalanche does occur, and he is therefore less likely to be dragged down by the avalanche or buried in it if he should be carried down. It is usually much safer to travel along ridges than in gullies, a flat-topped ridge being ideal. The skier should, of course, be sure that what looks like a flat ridge top is not an overhanging cornice.

The skier should be careful to observe and consider not only the snow on which he is skiing, but also the snow above and below him, since an avalanche falling from below may undermine the snow on which he is skiing, and an avalanche starting above him may sweep across his path. The bottom of a narrow valley is danger­ous if either slope is in danger of avalanche.

Precautions when danger exists.—Having selected the safest place to travel, if danger still exists, the following additional precautions should be taken:

1. The members of the party should travel at a suf­ficient distance apart, so that an avalanche would carry away only one of the party, leaving the others available for search. This frequently means a spacing between members of not merely a few yards, but of one or two hundred yards or more. Occasionally this rule of separa­tion may have to be abandoned when visibility is poor, owing to the danger, possibly greater, that some of the men may lose the route.
   
   
2. In getting off a dangerous slope, it is safer to go either straight up or straight down than to go across, since a vertical track does not cut the slope and reduce the snow bondage so much. It is usually wisest to travel on foot if possible. If it is necessary to go up with skis on, climbing skins should preferably be used, and in traveling straight down, it may be well to remove the skis unless the skier can take the steep course without danger of a fall.
   
   
3. Any necessary steps should be taken to permit quick removal of skis, poles, and pack, for reasons which will be explained later. This may necessitate loosening any ski bindings which cannot be removed by the flip of a single catch. Pole straps should be removed from the wrists and the belly strap on the pack unhitched.
   
   
4. If there is danger of avalanche from above, it is desirable to have one member of the party watch the dangerous slope while the lower slope is being crossed by the other members, one by one, in order that the watching member can give immediate warning if an avalanche starts.
   
   
5. The probability of being found when caught in an avalanche is greatly increased if each individual attaches to himself a 3/16-inch colored cord 30 yards or more in length. This is a greater precaution than the average per­son wishes to take, but it is of marked value in searching for victims. A somewhat shorter cord of approximately this diameter should normally be carried anyway, for use in making rescue toboggans and for other emer­gencies.
   
   
6. Occasionally a rope may be used in crossing a narrow gully or small wind slab. One member of the party crosses the dangerous portion while holding on to a rope which is being anchored by another member of the party who is on safe snow. Dangerous slopes should never be crossed, however, by skiers tied together by a rope, since they will become badly entangled if an ava­lanche occurs.
   
   
7. If the danger is from a light powder-snow ava­lanche, it is desirable to cover the mouth and nose with a cloth to avoid suffocation from the snow cloud which always accompanies such an avalanche.
   
   
8. It is important that mittens be worn in order to avoid frozen hands in the event of an avalanche.
   
   
9. Silence should be maintained in order to hear warning shouts or the first sounds of an avalanche.
   
   
10. Before crossing a dangerous slope, the leader of the party should make certain that all members under­ stand how to conduct themselves during an avalanche.

Conduct During an Avalanche

When actually caught in an avalanche, it is vitally im­portant that one avoid becoming buried. This can best be done by lying on the back (or stomach according to some authorities) with feet downhill and by maintaining a powerful swimming motion, being careful to keep the feet high, to avoid being tripped and rolled over head foremost. To accomplish this, it is obvious that one must have first removed his skis, poles, and pack before be­coming caught in the full sweep of the avalanche. The importance of removing this equipment cannot be over­emphasized.

In a wet-snow avalanche, it is particularly important to exert every ounce of strength to get one's head above the snow, or failing this, to obtain a space around one's head and chest as the avalanche comes to rest. This is because a wet avalanche frequently freezes solid as soon as it stops.

If an avalanche starts above a skier, he may be able to ski away from it if it is a wet-snow avalanche which moves slowly, but a wind-slab avalanche or dry-snow avalanche usually travels far too fast for escape by this method, and if such an escape it attempted and fails, the skier is caught with his skis on.

Avalanche Rescue Work

Marking victims' position.—If one or more members of a party are caught in an avalanche, other members in safe positions should carefully observe the path of those being swept away, in order to ascertain where they may be found when the avalanche comes to rest. Then, unless there is extreme danger that the undermining effect of the first avalanche will cause another, the members who best observed the probable position of the victims should remain in place to direct others, who should place mark­ers at the position.

Probing for victims.—The party must then immedi­ately probe the snow where the victims are thought to be. This should not be done in a haphazard fashion, but should be well organized under a leader. The area to be probed should be carefully but quickly laid out and the probing done systematically to cover each square foot of snow surface. Long poles are best for this purpose, but it is frequently necessary to use ski poles with the baskets removed, or reversed with the wrist-straps removed; or skis may be used. If the victims are not located in the anticipated position, the same systematic search should be extended, either moving from the initial point out­ward in all directions or starting from the top or bottom of the avalanche tip—whichever seems most likely to succeed quickly.

The searchers can usually best be arranged in a line, about 3 or 4 feet apart. This line is moved slowly for­ward, keeping in perfect alignment, with each member sounding with his pole or ski from left to right, making his soundings one foot apart in each direction. If the avalanche is quite deep and the victims are not found by this method, it is necessary to dig trenches about 9 feet apart, which permit probing horizontally through from one trench to the next.

If there are a large number of survivors, it may be de­sirable to send one or two for additional help, but if the number of survivors is small and help is some distance away, they should search for at least an hour before go­ing for assistance. The site of an accident should never be left without first carefully marking the place with mark­ers that will not be obliterated by a storm.

Victims will rarely survive very long in a wet-snow avalanche, and may have been crushed immediately by large blocks in a wind-slab avalanche; however, men have been known to survive for days when buried in light dry snow.

Are You Ready To Move Onto The Next Lesson? Click Here...