hundreds of adventure-seekers dream of climbing Qomolangma,

總有數以百計的冒險者夢想著攀上珠穆朗瑪峰，

also known as Mount Everest.

又稱埃佛勒斯峰。

At base camp, they hunker down for months

他們在基地營休養生息數月之久，

waiting for the chance to scale the mountain's lofty, lethal peak.

靜候攀登死亡高峰的最佳時機。

But why do people risk life and limb to climb Everest?

是什麼驅使人們冒著喪命或截肢的危險，也要登上此峰？

Is it the challenge?

是為了挑戰？

The view?

為了美景？

The chance to touch the sky?

為了觸摸天際？

For many, the draw is Everest's status as the highest mountain on Earth.

對許多人而言，最大的原因就是它身為地球第一高峰的名號。

There's an important distinction to make here.

登上此峰將使一切改觀。

Mauna Kea is actually the tallest from base to summit,

事實上，毛納基火山才是從山腳到山顛最高的山峰，

but at 8850 meters above sea level,

不過埃佛勒斯峰高於海平面8850公尺，

Everest has the highest altitude on the planet.

它則是地球表面最高的山。

To understand how this towering formation was born,

要弄懂這造塔運動的原理，

we have to peer deep into our planet's crust,

我們得深入地殼內部，

where continental plates collide.

在此大陸板塊彼此碰撞。

The Earth's surface is like an armadillo's armor.

地球的表面就好像犰狳的盔甲一般。

Pieces of crust constantly move over,

一片片的地殼不斷地彼此擠壓，

under,

向上或向下，

and around each other.

甚至繞著對方打轉都有可能。

For such huge continental plates, the motion is relatively quick.

以大陸板塊如此巨大的體積來看，他們移動的速度算快了。

They move two to four centimeters per year,

每年以2~4公分的速度移動著，

about as fast as fingernails grow.

約等於指甲生長的速度。

When two plates collide,

當兩個板塊碰撞時，

one pushes into or underneath the other, buckling at the margins,

一塊會擠入或鑽入另一塊，造成邊緣蜷曲

and causing what's known as uplift to accommodate the extra crust.

這導致了我們熟知的地殼隆起。

That's how Everest came about.

埃佛勒斯峰就是如此生成的。

50 million years ago, the Earth's Indian Plate drifted north,

5000萬年以前，印度洋板塊向北漂移，

bumped into the bigger Eurasian Plate,

並與體積較大的歐亞板塊撞在一塊，

and the crust crumpled, creating huge uplift.

使得地殼彎曲，形成巨大的隆起。

Mountain Everest lies at the heart of this action,

埃佛勒斯峰剛好地處這次板塊運動的中心位置，

on the edge of the Indian-Eurasian collision zone.

位於印度、歐亞板塊撞擊區的邊緣。

But mountains are shaped by forces other than uplift.

不過山脈的塑型受到隆起以外的力量所影響。

As the land is pushed up, air masses are forced to rise as well.

地表被推升的同時，空氣也隨之受到影響而上升。

Rising air cools, causing any water vapor within it to condense

上升的空氣因為溫度下降，致使其中的水蒸氣凝聚

and form rain or snow.

進而形成雨滴或雪。

As that falls, it wears down the landscape,

隨後雨滴或雪滴下，侵蝕了地表，

dissolving rocks or breaking them down in a process known as weathering.

使岩石溶解或碎裂，此過程稱作風化。

Water moving downhill carries the weathered material

水從山頂往山下流會順便夾帶風化後的碎片，

and erodes the landscape,

同時侵蝕地表，

carving out deep valleys and jagged peaks.

刻畫出深深的山谷與高聳的山峰。

This balance between uplift and erosion gives a mountain its shape.

抬升與侵蝕的拉鋸給予山脈今日的面貌。

But compare the celestial peaks of the Himalayas

可是，仰望直指雲端的喜馬拉雅山，

to the comforting hills of Appalachia.

再看看平緩的阿帕拉契山丘。

Clearly, all mountains are not alike.

很明顯可發現每座山的外觀大不相同。'

That's because time comes into the equation, too.

因為還得把「時間」這個因子列入考量。

When continental plates first collide, uplift happens fast.

大陸板塊互相碰撞時，抬升的速度混愾。

The peaks grow tall with steep slopes.

山頂會因此帶有陡峭的斜坡。

Over time, however, gravity and water wear them down.

不過隨著光陰流逝，地心引力和流水的雙重作用，會逐漸將它削平。

Eventually, erosion overtakes uplift,

直到侵蝕取代抬升，

wearing down peaks faster than they're pushed up.

即下降的速度快於上升。

A third factor shapes mountains: climate.

第三個影響山的外觀的因子：氣候。

In subzero temperatures, some snowfall doesn't completely melt away,

在零度下低溫的環境哩，落雪並不會完全融化，

instead slowly compacting until it becomes ice.

反之，它們會慢慢壓實，而後變成冰。

That forms the snowline, which occurs at different heights around the planet

這形成了雪線，其高度在全球的各地都不盡相同，

depending on climate.

得視氣候而定。

At the freezing poles, the snowline is at sea level.

在冰凍的極區，雪線高度就等於海平面。

Near the equator, you have to climb five kilometers before it gets cold enough

赤道附近，得往上爬5000公尺，

for ice to form.

溫度才低到足以化雪為冰。

Gathered ice starts flowing under its own immense weight

聚集成堆的冰因自身重量而開始滑動，

forming a slow-moving frozen river known as a glacier,

這移動速度緩慢的冰凍之河就叫冰河。

which grinds the rocks below.

冰河會不斷磨擦其底下的岩石。

The steeper the mountains, the faster ice flows,

山的坡度越陡，冰河流速越快，

and the quicker it carves the underlying rock.

刻蝕底下岩石的速度也跟著加快。

Glaciers can erode landscapes swifter than rain and rivers.

冰河侵蝕地表的功力超過了下雨和河流。

Where glaciers cling to mountain peaks, they sand them down so fast,

由於冰河緊貼著山壁，它們可以快速地將之磨平，

they lop the tops off like giant snowy buzz saws.

效率跟用雪做成的巨大電鋸砍樹一樣好。

So then, how did the icy Mount Everest come to be so tall?

那麼，埃佛勒斯峰到底是如何長這麼高的？

The cataclysmic continental clash from which it arose

生於冰河時期的大陸巨變，

made it huge to begin with.

造就了埃佛勒斯峰先天傲人的高度。

Secondly, the mountain lies near the tropics,

第二是，位處熱帶地區，

so the snowline is high, and the glaciers relatively small,

雪線很高導致冰河相對較小，

barely big enough to whittle it down.

缺乏刻蝕山體的力量。

The mountain exists in a perfect storm of conditions

天時、地利具備，

that maintain its impressive stature.

埃佛勒斯峰便得以保持峗然聳立之姿至今。

But that won't always be the case.

但事情不會總是一成不變。

We live in a changing world where the continental plates,

身處一個瞬息萬變的世界，

Earth's climate,

大陸板塊，地球的氣候，

and the planet's erosive power

還有地球侵蝕的力量，

might one day conspire to cut Mount Everest down to size.

終將會有聯手將埃佛勒斯峰夷為平地的一天。

For now, at least, it remains legendary in the minds of hikers,

至少時至今日，

adventurers,

對登山者、冒險家、和追夢者等人，

and dreamers alike.

埃佛勒斯峰依然在他們心中保有傳奇的地位！