Unit 10(1)            Terror in the Mountains

A  What is incredibly beautiful, yet absolutely terrifying and deadly at the same time? For anyone above the snowline in the mountains, there is little doubt about the answer. Avalanche—the word strikes fear into the heart of any avid skier or climber. For those unfortunate enough to be caught up in one, there is virtually no warning or time to get out of danger and even less chance of being found. The ‘destroyer’ of the mountains, avalanches can uproot trees, crush whole buildings and bury people metres deep under solidified snow. Around the world, as more and more people head to the mountains in winter, there are hundreds of avalanche fatalities every year.

B  A snow avalanche is a sudden and extremely fast-moving ‘river’ of snow which races down a mountainside (there can also be avalanches of rocks, boulders, mud or sand). There are four main kinds. Loose snow avalanches, or sluffs, form on very steep slopes. These usually have a ‘teardrop’ shape, starting from a point and widening as they collect more snow on the way down. Slab avalanches, which are responsiblefor about 90% of avalanche-related deaths, occur when a stiff layer of snow fractures or breaks off and slides downhill at incredible speed. This layer may be hundreds of metres wide and several metres thick. As it tends to compact and set like concrete once it stops, it is extremely dangerous for anyone buried in the flow. The third type is an isothermal avalanche, which results from heavy rain leading to the snowpackbecoming saturated with water. In the fourth type, air mixes in with loose snow as the avalanche slides, creating a powder cloud. These powder snow avalanches can be the largest of all, moving at over 300 kmh, with 10,000,000 or more tonnes of snow. They can flow along a valley floor and even a short distance uphill on the other side.

C  Three factors are necessary for an avalanche to form. The first relates to the condition of the snowpack. Temperature, humidity and sudden changes in weather conditions all affect the shape and condition of snow crystals in the snowpack which, in turn, influences the stability of the snowpack. In some cases, weather causes an improvement in avalanche conditions. For example, low temperature variation in the snowpack and consistent below-freezing temperatures enable the crystals to compress tightly. On the other hand, if the snow surface melts and refreezes, this can create an icy or unstable layer.

D  The second vital factor is the degree of slope of the mountain. If this is below 25 degrees, there is little danger of an avalanche. Slopes that are steeper than 60 degrees are also unlikely to set off a major avalanche as they ‘sluff’ the snow constantly, in a cascade of loose powdery snow which causes minimal danger or damage. This means that slabs of ice or weaknesses in the snowpack have little chance to develop. Thus the danger zone covers the 25 to 60 degree range of slopes, with most avalanches being slab avalanches that begin on slopes of 35 to 45 degrees.

E  Finally, there is the movement or event that triggers the avalanche. In the case of slab avalanches, this can be a natural trigger, such as a sudden weather change, a falling tree or a collapsing ice or snow overhang. However, in most fatal avalanches, it is people who create the trigger by moving through an avalanche-prone area. Snowmobiles are especially dangerous. On the other hand, contrary to common belief, shouting is not a big enough vibration to set off a landslide.

F  Anyone moving through snow in the mountains should understand the danger signals and follow some basic rules. Taking an approved avalanche safety course is an essential first step. Skiers and climbers should be up-to-date with local warning systems and check any avalanche forecast hotline or website. They should also be aware of their surroundings, avoid areas that have signs of previous avalanche activity and monitor the weather conditions carefully. Basic equipment should include a rescue beacon with fresh batteries, an inexpensive inclinometer to measure the angle of slopes and an avalanche probe.

G  Beautiful but deadly, avalanches kill increasingly numbers of winter sports enthusiasts every year as more and more people enjoy the mountains in winter. As it is easier to avoid an avalanche than to surviveone, it is vital for snow enthusiasts to recognise the three basic factors which contribute to avalanches. An awareness of the condition of the snowpack, the angle of the slope and the ways in which an avalanche may be triggered can be the difference between life and death in the mountains.

山中的恐怖

A  有什么东西是美得令人难以置信，但同时也是绝对令人恐惧和致命的呢？对于任何置身在山中雪线以上的人来说，答案几乎没有什么悬念。雪崩——这个词能将恐怖感击入任何热切爱好滑雪和登山者的心中。对于那些不幸碰上一场的人来说，几乎没有事先预警或时间可以逃离危险之外，被找到的机会就更加渺茫了。雪崩是群山的“破坏者”，能将树木连根拔起、推倒整栋建筑以及把人们埋在结结实实的雪层下几米处。纵观全球，随着越来越多的人们在冬日里向山中进发，每年都有数百位雪崩遇难者。

B  一场雪崩也就是一条突然而以极快速度冲下山坡的雪的“河流”（也可以有石头、大石块、泥浆或沙子的崩流）。雪崩有四种主要的类型。散雪雪崩，或称小雪崩(sluff)，形成于非常陡峭的山坡之上。这些通常有着一种“泪滴”的形状，从一个点开始成形并在一路向下的过程中聚集更多雪而膨胀加宽。板状雪崩(slab avalanche)要为大约90%与雪崩有关的死亡率负责，它发生在一层结实板结的雪整片断裂并以难以置信的高速滑下山坡的时候。这层雪有可能达到几百米宽和好几米厚。一旦它停止了运动，开始像混凝土那样收缩凝固，对于任何埋在雪层下面的人来说都是极度危险的。第三种是等温线雪崩(isothermal avalanche)，其起因是大雨导致雪堆中浸透了水分。在第四种类型中，在雪崩滑行的过程中空气混进了松散的雪里，产生出一片雪粉云。这些雪粉状雪崩可以成为所有类型的雪崩中规模最大的一种，以每小时300公里的速度移动，卷夹着10,000,000吨甚至更多的冰雪。它们可以沿着一条峡谷的底床涌动，甚至可以冲上一小段对面的山坡。

C  要形成一场雪崩必须有三个因素。第一个与雪堆的状况有关。温度、湿度和气候条件的突然变化都会影响雪堆中冰雪晶体的形状和情况，而这些继而又会影响雪堆的稳固性。在一些情况下，天气会引起雪崩条件的改善。例如，雪堆中的低温变化和持续的冰冻以下温度(也就是温度一直保持在结冰温度以下)使得冰雪晶体紧紧地缩聚在一起。而另一方面，如果雪层表面融化再重新冻结，这就有可能产生一个多冰或不稳定的层面。

D  第二个至关重要的因素是山坡的倾斜度。如果这个倾斜角度在25度以下，几乎没有发生雪崩的危险。倾角大于60度的那些山坡也不太可能会引发一场大型雪崩，因为它们始终在持续不断地“滑落”小雪，这些纷纷扬扬而下的松散雪粉造不成多大的危险或损害。这意味着雪堆中的冰层或脆弱不稳定处没有什么机会可以发展壮大。这样一来，危险区也就是覆盖了倾角为25到60度的山坡这个范围，其间的大多数雪崩都是始于倾角在35到45度之间山坡上的板状雪崩。

E  最后，还有一个因素是引发雪崩的运动或事件。在板状雪崩的类型中，这可以是一个天然的诱发因素，例如一场突然的气候变化、一棵倒下的树或是悬挂在上方的冰或雪团突然掉下。不过，在大多数致命的雪崩中，是人们在雪崩易发区域中活动从而制造出了诱因。雪地车尤其危险。另一方面，与人们通常以为的那样相反，大声呼喊并不足以产生足够大的震动以引发一场山体雪地滑坡。

F  任何在山中穿越雪地行动的人都应当懂得危险信号并遵守一些基本规则。上一门经核准的(approved的翻译，也就是这门课得在指定的有资质认证的机构去上)雪崩安全课程是至关重要的第一步。滑雪和登山者应当及时了解当地的预警系统并随时查询任何雪崩预告热线或网站。他们还应当关注自己所处的环境，避开那些有着先前雪崩活动告示牌的地区并仔细留意天气条件。基础装备应当包括一只电量充足的救援信号灯，一架无需昂贵的(其实也就是简易便携式的，简装所以不贵，因此inexpensive)倾角仪以备丈量斜坡的角度和一台雪崩探测器。

G  雪崩美丽但却致命，随着越来越多的人们去山中乐享冬季，它所杀死的冬季运动热情爱好者的数目每年都在上升。既然躲避一场雪崩比从一场雪崩中幸存下来要更加容易，那么对于冰雪爱好者们来说，要充分认识导致雪崩的三个基本因素也就是至关重要的了。对雪堆情况、山坡倾角和雪崩可能被引发方式的认识与否可以成为在山中生与死之间的差别。