Reading Passage 2
Nature’s destructive fury is unleashed on mountainsides around the world
A) Hurtling down a mountainside at speeds of up to 300 kilometres an hour, an avalanche is at once both a terrifying sight and a spectacle of nature. The power of gravity pulls the snow mass down the mountain slope, capturing all in its path, from rocks, trees, and ice to, from time to time, human victims. Avalanches are caused by a wide range of factors, including the steepness of the mountainside, the weather, the terrain, the snowpack conditions and human activity. Avalanches occur in all parts of the world, in the northern hemisphere and the southern—wherever there are slopes steep enough for the snow to slide down, sometimes recording as much as 250,000 cubic metres of snow descending at unimaginable speeds and force, destroying all in its path.
B) An avalanche is an occurrence of nature whereby an entire layer of snow, or snowpack, separates naturally, or from human activity, and descends with rapid downward force, building up speed and air pressure ahead of it, with phenomenal destructive force. An avalanche has three main parts, the starting zone, the avalanche track and the runout zone. The starting zone is a volatile area of a slope where snow that is unstable can fracture and separate from the compacted snow and start to move downward. Usually, this occurs high up the slope of a mountain, but can happen anywhere there is a slope, and the usual cause is when the weight or force of the snow is greater than the strength holding it together. The avalanche track is the route the cascading snow follows, and is often a noticeable track following open or chute-like terrain, away from dense growths of trees, which indicates that other avalanches may have occurred, and often ending with large collecting areas where there is an abundance of debris, such as in gullies or flattened open areas. This is known as the runout zone, which is where the snow is usually piled the highest, with mounds of debris deposits.
C) There are three main types of avalanches: wet snow avalanches, dry snow avalanches and slab avalanches. Wet snow avalanches are often thought of as the least dangerous, usually occurring naturally in the spring season because of melting snow from the increasing temperatures. They are considered less dangerous because of the slow speed, due to friction, but can cause significant destruction because of their large mass. Water saturation is a key point, due to the melting, and they pull boulders, earth and vegetation with them. Dry snow avalanches are normally the largest, consisting of an enormous powder cloud masking huge volumes of a rapidly moving snowpack and occur at any time or for any reason. These avalanches can reach speeds of 300 km/hr, and can carry up to 10,000,000 tonnes of snow for incredibly long distances, and often uphill as they come to rest. Finally, some experts consider slab avalanches as the most dangerous, as a slab, or block, of snow separates from the main body of snow and cascades downward. A ‘crown fracture’ appears at the top and ‘flank fractures’ are created vertically, separating the block of snow which speeds downhill, destroying everything. Interestingly, these types of avalanches often leave ‘walls’ carved in the snow where the avalanche has broken away. Slab avalanches account for most related fatalities, and are often caused by human activity, notably skiers.
D) Other factors that can cause avalanches include natural conditions such as wind, weather, composition of the snow, storms, sunlight and moisture. Interestingly, coastal environments limit many of the dangerous aspects of mountainous conditions, with an ongoing stabilization of the snowpack due to a continuous freeze-thaw cycle moderating weather extremes. Very cold temperatures can also cause critical circumstances which give rise to avalanches, by affecting the stability of the snow pack, with differences in ground temperatures contrasting with the ambient air temperature, thus affecting moisture content, crystal formation and varying thicknesses of snow. Storms, be they rain or snow, lead to weight variations, with heavy precipitation on top, and less chance of snow bonding to secure a stable weight-load. And sunlight introduces a number of factors, melting, re-freezing and radiation loss which means significant variations in the heat/cooling process, which impacts on the stability of the snow pack.
E) So, what can be done to prevent, predict or control this unleashing of nature’s destructive forces? In areas where avalanches present a major threat, such as mountainous communities, ski resorts and transportation facilities, there are a number of initiatives being introduced, because holding back Mother Nature has always been a long-held, but not always successful, dream. Explosives are regularly used in mountainous areas, armies being employed to fire high-decibal cannons which trigger shock waves to loosen snow packs, and other concussion devices dropped from helicopters or hand-launched. Protective fences can direct snow build-up to help prevent snow packs being formed, and there is often construction of avalanche dams to re-direct falling snow, or the building of earth mounds to slow the slide of avalanches. Lastly, to protect human life in the possibility of avalanche conditions, snow shelters have been constructed to withstand the impact of the force of snow, shielding human life, vehicle traffic and residential dwellings.
F) Avalanches cannot accurately be predicted, although the conditions can be monitored, studied and assessed. Snow and weather conditions, including temperature, wind and moisture, are a reliable guide, as well as human activity, recent history and forecasts of worsening conditions. However, unfortunately, disasters have occurred. And will continue so. During World War I, between 40,000 and 80,000 soldiers died in the mountainous regions of central Europe, in particular on the Austrian-Italian battlefields, and it has been determined that many were killed as a result of artillery fire, the concussive effects resulting in avalanches. Numerous ski resorts and their communities have unfortunately suffered devastating avalanches, notably in Turkey in 1993, when 43 climbers lost their lives, and in France in 1999, when 12 people were buried under 100,000 tonnes of snow, and in the same year, 31 people died in Austria in one avalanche.
G) There are various classification systems for avalanches, but none that is universally recognized. Canada and the United States use one system, defining risk levels using various factors, while Europe employs a different rating system with different criteria, and other alpine nations utilize varying systems which reflect different aspects of risk and outcomes. Avalanches pose a constant threat, and work is constantly being done to forecast, and mitigate, the risks and outcomes of avalanches. Survival is possible for those caught in this most terrible of natural circumstances, and future work and investigation is vital to ensure the safety of those caught in one of nature’s most destructive unleashings.