from the book, "Our Fascinating Earth"
An avalanche is a sudden cascading of snow and ice that occurs all too frequently on the steep slopes of the world's snow—laden mountains. It is one of nature's greatest destructive forces, easily ranking with tornadoes, hurricanes, earthquakes, and floods as one of the more irresponsible, unpredictable natural acts of violence.
In mountainous areas where the slope is greater than thirty—five degrees, deep piles of snow often lie in a critical state of balance. A simple event such as the falling of a tree limb or a lump of snow, the weight of a skier, the noise of a pistol shot, or even the sound of a human voice can trigger a slide involving millions of tons of snow. In a matter of minutes entire villages can be smothered, causing inescapable death and destruction.
Scientists have attempted to classify avalanches, but all the variables working together make it difficult for an avalanche to stick to a single category. It may be composed of dry, powdery snow and airborne, or of wet snow flowing along the ground, or a combination. It may break away from the slope at a single point or as a large slab. The way it proceeds down a slope is dependent on the terrain, whether it is channeled in a gully or unconfined in an open area.
Initially the mass of snow moves slowly, but it can quickly build up to speeds of over 200 miles per hour. In such a slide the frontal snow will lift off the ground, forming a whistling, swirling mass of powderlike mist. The powdery mist is often followed by huge solid masses of snow and ice. The high velocity of a powder avalanche creates enormous air pressures in front of it, resulting in hurricane—force winds. Such a powerful wind once blew a tourist bus off a bridge in Austria, killing twenty—three skiers. Snow from the avalanche never even touched the skiers.
The white fury of an avalanche is truly the skier's nightmare. Val d'Isere, France, was a popular ski resort until February 1970. Without warning some 100,000 cubic yards of snow pulled loose from the adjacent mountains and smacked into the town at a speed of over 120 miles per hour. Within minutes forty—two people were buried under mountains of snow 300 feet deep. Survivors said they had the sensation that a tremendous explosion had occurred.
Although statistics for avalanche death and destruction are significant, most avalanches do no damage to people or property because they occur in uninhabited areas. Not surprisingly, the most frequent and vicious avalanches occur in the Himalayas, but casualties are rare. Because the Alps are the most densely populated snow—covered mountain range, theirs is the highest toll of death and destruction. Nevertheless a casualty list of about 200 people per century suggest that Alpine dwellers understand how to live with or through an avalanche and how to anticipate, control, and avoid it.
The most common avalanches are composed of snow, but some, usually more dangerous and destructive, are of ice or rock. The most deadly avalanche of the twentieth century began at the ice—covered peak of Peru's highest mountain, Nevada de Huascaran, on January 10, 1962. Two million cubic yards of ice broke loose from the four—mile—high peak, gathering blocks of granite, slate, soil, and debris as it made the mile—a—minute descent to the floor of the valley nine miles away. Its final toll was nine villages, one town, and 4,000 people. More recently, on May 31, 1970, Nevada de Huascaran had occasion to outstrip its previous record with a more massive, violent, and destructive avalanche. With a front over 1,000 yards wide, the mass of ice and rock poured down the mountain at speeds up to 248 miles per hour. Casualties were estimated at up to 25,000, making this by far the most cataclysmic avalanche on record.
During World War I avalanches were used extensively, and very effectively, as weapons. A conservative estimate of Austrian and Italian Alpine troop casualties between 1915 and 1918 was 40,000; other estimates, with information obscured by censorship, ran as high as 80,000. The method was simple — shell fired into a snow—laden slope could release tons of snow on the enemy below. In one 48—hour period 3,000 Austrians and an equal number of Italians were entombed by induced slides. In all, more Alpine soldiers were killed by avalanches during the war than by all the bullets and shells that were fired at them.
Just as the people in snowslide areas know how to set off an avalanche, they have also learned how to stop many of them. A thickly wooded area is the best defense, for it can prevent an avalanche from forming and can arrest all but the most powerful. At one time cutting a tree on a Swiss Alpine slope carried the death penalty. Artificial barriers include rows of fences that hold snow in place and keep a slide form developing or long walls constructed at an angle to the slope so that snow will be deflected to places where it can do little harm. The uphill side of many Swiss buildings is wedge—shaped, thereby splitting an avalanche into two harmless halves. Trans—Alpine railways and highways are protected in vulnerable areas by tunnels or galleries so that the avalanche will slide harmlessly over them.
For a person who has been caught in an avalanche without a modern electronic sensor, the best escape is via dog. Trained dogs have been used for centuries to search out human victims, and many stories of uncanny rescues are true. One such event was recorded in Zurs, Austria. It was early in the morning; the local postman was busily delivering the mail. While driving the mail truck, he was so intent on negotiating the hazardous road that he failed to notice a blanket of white approaching. A sudden avalanche swept down, completely burying him and his vehicle.
Although he was missed, nobody had any idea where to look for him. No one, that is, except his dog, which came to a certain spot and refused to move from it for three days. The persistent whining of the dog finally aroused the curiosity of the townspeople, enough that they decided to dig into the snow where the dog was keeping vigil. Here they uncovered the missing mail truck with the man still in the driver's seat, unconscious but alive. Almost miraculously he had survived having been entombed in the snow. Although the mailman recovered completely, the mail truck did not. Eventually it was sold for junk.
The worst avalanche disaster in the United States occurred at the Wellington Railroad Station, Washington, in the Cascade range. On March 1, 1910, a huge avalanche suddenly crashed down on the station. As its fury continued, it swept over a ledge and into a deep canyon three locomotives, several carriages, a large water tank, and the station house itself. More than one hundred people met their deaths.
Most victims of a thunderbolt of snow realize that if they are not rescued within an hour or two, they probably will not live to witness the rescue. They have little choice but to spend the time wisely: motionless, silent, hopeful.