Name: 【TED-Ed】Why is Mount Everest so tall? - Michele Koppes
Uploaded: 2016-06-18T21:59:59.000Z
Duration: 4 min 53 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

hundreds of adventure-seekers dream of climbing Qomolangma,

At base camp, they hunker down for months

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

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

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

There's an important distinction to make here.

Mauna Kea is actually the tallest from base to summit,

Everest has the highest altitude  on the planet.

To understand how this towering formation was born,

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

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

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

They move two to four  centimeters per year,

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

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

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

and the crust crumpled, creating huge uplift.

Mountain Everest lies at the heart of this action,

on the edge of the Indian-Eurasian collision zone.

But mountains are shaped by forces other than uplift.

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

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

As that falls,  it wears down the landscape,

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

Water moving downhill carries the weathered material

carving out deep valleys and jagged peaks.

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

But compare the celestial peaks of the Himalayas

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

When continental plates first collide, uplift happens fast.

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

wearing down peaks  faster than they're pushed up.

A third factor shapes mountains: climate.

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

instead slowly compacting  until it becomes ice.

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

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

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

Gathered ice starts flowing under its own immense weight

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

The steeper the mountains,  the faster ice flows,

and the quicker it carves  the underlying rock.

Glaciers can erode landscapes swifter than rain and rivers.

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

they lop the tops off like giant snowy buzz saws.

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

The cataclysmic continental clash from which it arose

Secondly, the mountain lies  near the tropics,

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

The mountain exists in a perfect storm of conditions

We live in a changing world  where the continental plates,

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

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