 nation and our freedoms, we must be prepared to conduct military operations in every type of terrain and in every climate. Mountain regions are always a source of danger to the untrained or unwary soldiers. There are risks to be faced the year round, but winter, with its extreme cold, high winds and severe snowstorms covering the areas with heavy snow, multiplies the hazards tremendously. It is only the specially trained and equipped soldier who can perform his mission under conditions of this nature because snow alone increases the difficulties of movement. And the ability of the snow to avalanche is an ever-present source of danger. Until quite recently, little was known about the avalanche except that many brought death and destruction to man and his possessions. In Europe, avalanches have long been called the white death. And in military operations in the eastern Alps in World War I, more troops were destroyed by this killer than lost their lives in actual combat in that particular region. A snow avalanche is a mass of unstable snow set into motion by a number of contributory causes. In army terminology, the word avalanche is always taken to mean a snow avalanche. Snow, its structure, the changes that take place in the crystals, the forces that cause it to avalanche are quite complex. But a soldier must know some basic facts about snow and its behavior to maneuver in it successfully. One fact is that every mountainous slope deeply covered with snow should be looked upon with grave suspicion by all who have a mission to perform in such terrain. It should always be borne in mind that any layer of snow 12 inches or more in depth on an incline has the potential of sliding and producing an avalanche. A mass of snow has plastic qualities. It tends to flow downhill under the influence of gravity. This behavior is known as snow creep, which is very slow and difficult to notice. But the tension it produces within the layers of snow is often a factor in causing the snow to avalanche. The thumb is that any snow mass lying on a slope at an angle of approximately 25 degrees should be considered hazardous. Avalanches are most common on angles of 25 to 60 degrees and higher. Slides at lesser angles are rare. The contour of a mountain side is also an important factor in avalanche occurrences. These slopes are either concave or convex in profile or a combination of both. On a concave slope, the layers of the snow mass tend to be compressed, resulting in increased cohesion and generally stable conditions. On convex slopes, the snow layers are under great tension. This in turn reduces the internal cohesion of the snow layers. The sheer weight of the snow mass makes avalanching of this type of slope quite common. While snow-covered mountain slopes can pose a threat, terrain features such as ravines and gullies can present a double threat. Not only may an avalanche occur from either side, but from both sides at the same time. Movement through such areas must be made with great caution. Certain terrain features, on the other hand, can help reduce the danger of snow slides. Such types of mountain vegetation, such as bushes and trees, can be a stabilizing influence on snow-covered slopes. But this growth can be trusted only if it's dense and can be seen to protrude well above the cover of snow. Possessing the same ability of holding snow on a slope are such land features as terraces, rock outcrops, heavily forested slopes are usually positive barriers to avalanches since the trees help to anchor the snow and inhibit its release. But they may not be a complete protection from slides that may originate from above the timber line. Such slides may still find their way through the forest growth to the valley below. Just as they do where trees are scattered and offer little defense against a rapidly descending snow mass, avalanches are classified into two main groups based mainly on the type of snow involved. The first group represents the loose snow avalanches which are further subdivided into dry, damp, and wet snow types. To the second group belong the packed snow avalanches called wind slabs. Wind slabs are also subdivided into dry, damp, and wet types. And finally the merging of both types is called a combination avalanche. Let us observe a dry snow avalanche. It originates at a small point in the snow of a slope. As it descends, it fans out like a wave increasing in width and depth and attaining great speed. The light, fluffy snow gives rise to a wind blast and snow dust cloud that moves with a force of a hurricane. Some have been clocked as high as 300 kilometers an hour. It uproots trees, destroys structures, and snuffs out lives by suffocation. And this may occur even when these objects are not directly in the path of the oncoming snow mass. Wet or damp, loose snow avalanche also starts at a narrow point on the surface of the snow and increases in width and depth as it descends. However, due to the moisture in the snow, it tends to travel in a narrower and more definite path and at a slower pace than the dry snow avalanche. Unlike the dry snow avalanche, the wet snow produces little wind blast, but its moisture gives it a heavier, more solid mass and thus a great destructive force. In addition, the friction caused by this moisture will cause a wet snow slide to slow down rapidly and pile up in a mass of snow boulders. The wind slab avalanche is the most treacherous killer of the avalanche family. With its hard, chalky white wind formed surface, it has the ability to hang in an unstable condition for weeks and even months. Even long after other snow has stabilized, it can slide when least expected. Its characteristics differ from those of the loose snow avalanche. The wind slab originates or fractures across a wide front and in depth. The entire slab moves almost instantaneously. As it races down the slope, it breaks into large blocks. At its actual speed, it becomes evident why the wind slab is called the big killer. Often times, a wind slab will trigger a loose snow avalanche or a loose snow avalanche may set a wind slab into motion. This merger of both types is called a combination avalanche. Avalanches start with a mass of unstable snow. In each case, however, every avalanche must have a trigger to start it. There must be some force or combination of forces to release the mass of snow at a particular time and place. That is probably the most common of all avalanche triggers. A new layer of snow or the weight of an individual can easily be the trigger that sends the snow mass downward. The shearing action of snowshoes or a pair of skis can be the force that cuts the bonds holding the snow to the slope. So can the shearing action provided by a rock, snowball or any other object falling from above. A cornice is a snow formation built up by the wind on the lee side of a narrow mountain ridge or crest. It plays a large role not only in the development of cornices but of other avalanche hazards for it often has the power to carry huge quantities of snow from one place and deposit it in another. It is also the main force in producing wind slab formations. Cornice overloaded with snow or weakened by climatic changes a cornice will fall. The debris is not only dangerous to anyone caught beneath it but its shearing action may also start an avalanche on the slope below. Vibration is a triggering action related to shearing but unlike all other triggering it can operate at long range. Avalanches can be set off by sound and shock waves such as loud sharp sounds of weapons firing and other explosive sounds transmitted through the air. Snow slides may also be started by vibrations transmitted through the earth itself. These can result from the movement of heavy equipment such as tanks, bulldozers and from explosive blasts of varying intensities. Waves and or vibration released by one avalanche can often trigger another one. Wind and great temperature changes trigger more avalanches than any other factors. A rise in temperature weakens the cohesive bonds of the snow. A sharp fall on the other hand increases the brittleness and tension of a deep snow cover and its tendency to break away and slide. Despite the dangers however conditions imposed by an enemy may force us to conduct both defensive and offensive military operations in certain alpine type areas in different sections of the world. Let us suppose that a reconnaissance party has the mission to establish a route in a given mountain area. In this case it is very important to first make a visual reconnaissance from the air. The leader and his assistants make use of a helicopter to cover the terrain in question. Upon completion of the aerial reconnaissance the patrol moves out with the necessary gear to carry out the mission. There can be no doubt that avalanching snow can be an ever present menace to troops operating in snow covered mountainous terrain. But many of these hazards can be prevented or eliminated. There are a number of methods called artificial triggering that troops can employ to achieve stabilization of menacing slopes and cornices. Utilizing men on skis or snowshoes is one method of neutralizing small avalanche areas. By this means the snow is either made to settle and thus become stabilized or the weight of the man and the shearing action of his skis will start the slide. In either case the avalanche hazard will be removed. Another method that may be utilized if the snow mass is very unstable is the detonation of hand grenades just below the crest of a critical slope. A more effective method to stabilize dangerous slopes or cornices is the use of explosive charges. In order to place the charge a hole must be dug in the snow which can be done with a ski pole. While the demolition man is belayed from a safe place by a rope he prepares the charges for detonation. Normally several interconnected charges have to be used which are detonated simultaneously to achieve satisfactory results. After the charge has been properly placed into the hole it must be tapped to ensure its effectiveness. This type of detonation of threatening slopes and cornices must always take place from safe protected positions and by remote control. Years of danger must be clearly marked with flags or signs before and during triggering operations and should be off limits to all personnel. To eliminate the risk and burden of climbing to dangerous ridges and crests a variety of small military weapons can be used to dislodge the snow and reduce avalanche dangers. To stabilize a slope at a short distance a rifle grenade may be used with good results. All methods of triggering however are not simply a matter of firing a weapon at a mass of snow. Shots must be placed where they will be most effective. When artificial triggering produces avalanching it indicates that the snow mass was definitely unstable. When nothing occurs it generally indicates stability. But this should not be accepted as fact until all other slopes in the locality have also been tested. Triggering operations used as defensive and protective measures can of course be employed as offensive weapons. Avalanches set off within enemy lines can destroy enemy troops and wipe out enemy equipment and installations. Every soldier with a mission in this type of terrain is provided with proper training and equipment. He will have little reason to fear for the success of his mission.