VOA科学技术2024--Everest Growing Taller than Expected

 

Mount Everest, standing¹ 8.85 kilometers above sea level, is Earth's tallest mountain.

And Mount Everest is still growing.

Mount Everest and the rest of the Himalayas are continuing on an upward movement that began at their birth around 50 million years ago. The mountains are a product of a collision between Eurasia and the Indian subcontinent.

But Everest is growing more than expected. And, scientists now think they know the reason why.

Everest's growth has to do with the major joining, or merger², of two nearby river systems. The Kosi river joined with the Arun river around 89,000 years ago, the researchers estimated.

This change in the area's river system has led to Everest gaining around 15-50 meters in height.

That suggests an upward movement rate of about 0.2-0.5 millimeters per year.

The geological process at work, researchers said, is called isostatic rebound³.

Isostatic rebound involves the rise of land masses on Earth's crust when the weight of the surface declines. The crust, Earth's outermost⁴ part, floats atop hot, semi-liquid rock.

In this case, the joining of the rivers resulted in increased erosion which carried off large amounts of rock and soil. This reduced the weight of the area near Everest.

"Isostatic rebound can be likened to a floating object adjusting its position when weight is removed," said Jin-Gen Dai of China University of Geosciences in Beijing.

Dai is one of the leaders of the study published recently in Nature Geoscience.

"When a heavy load, such as ice or eroded⁵ rock, is removed from the Earth's crust, the land beneath slowly rises in response, much like a boat rising in water when cargo⁶ is unloaded," Dai added.

The researchers, who used numerical models to study the development of the river system, estimated that isostatic rebound accounts for about 10 percent of Everest's yearly upward movement, or uplift rate.

This geological process is seen in other places around the world.

"A classic example is in Scandinavia, where the land is still rising in response to the melting of thick ice sheets that covered the region during the last Ice Age. This process continues today, affecting coastlines and landscapes, thousands of years after the ice retreated," Dai said.

Study co-writer Adam Smith, a University College London doctoral student, said GPS measurements show the continued rising of Everest and the rest of the Himalayas.

This uplift is faster than the continued surface erosion caused by wind, rain and river flow. As this erosion continues, Everest's uplift rate from isostatic rebound may increase, Smith said.

Neighboring mountains, including Lhotse, the world's fourth highest, and Makalu, the fifth highest, also get a boost from the same process. Lhotse is experiencing an uplift rate similar to Everest. Makalu has a slightly higher uplift rate.

Dai said that the research shows our planet's changing nature. Even a seemingly unchanging element like Mount Everest is "subject to ongoing⁷ geological processes, reminding us that Earth is constantly changing, often in ways imperceptible in our daily lives."

Earth's rigid⁸ outer part is divided into large plates that move slowly over time. The Himalayas rose following a collision between two plates.

Everest is located on the border between Nepal and the Tibet Autonomous⁹ Region of China. It was named for George Everest, a 19th century British surveyor in India.

"Mount Everest occupies a unique place in human consciousness," Dai said.

"Physically¹⁰, it represents Earth's highest point," giving it a lot of importance simply because of its size, Dai explained.

He added that Everest has cultural importance to local Sherpa and Tibetan communities. Worldwide, Dai said, the mountain represents a big test for human endurance.

Words in This Story

crust - n. the outer part of a planet, moon, or asteroid¹¹

erosion - n. the process of diminishment or destruction by degrees

response - n. something constituting a reply or reaction

region - n. a broad geographic¹² area distinguished¹³ by similar features

imperceptible - adj. extremely slight, gradual, or subtle

surveyor - n. one who determines and delineate the form, extent, and position of a tract¹⁴ of land by taking measurements

unique - adj. being without like or equal

1 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

2 merger   

n.企业合并，并吞

参考例句：

• Acceptance of the offer is the first step to a merger.对这项提议的赞同是合并的第一步。
• Shareholders will be voting on the merger of the companies.股东们将投票表决公司合并问题。

3 rebound   

v.弹回；n.弹回，跳回

参考例句：

• The vibrations accompanying the rebound are the earth quake.伴随这种回弹的振动就是地震。
• Our evil example will rebound upon ourselves.我们的坏榜样会回到我们自己头上的。

4 outermost   

adj.最外面的，远离中心的

参考例句：

• He fired and hit the outermost ring of the target.他开枪射中了靶子的最外一环。
• The outermost electron is shielded from the nucleus.原子核对最外层电子的作用受到屏蔽。

5 eroded   

adj. 被侵蚀的，有蚀痕的 动词erode的过去式和过去分词形式

参考例句：

• The cliff face has been steadily eroded by the sea. 峭壁表面逐渐被海水侵蚀。
• The stream eroded a channel in the solid rock. 小溪在硬石中侵蚀成一条水道。

6 cargo   

n.(一只船或一架飞机运载的)货物

参考例句：

• The ship has a cargo of about 200 ton.这条船大约有200吨的货物。
• A lot of people discharged the cargo from a ship.许多人从船上卸下货物。

7 ongoing   

adj.进行中的，前进的

参考例句：

• The problem is ongoing.这个问题尚未解决。
• The issues raised in the report relate directly to Age Concern's ongoing work in this area.报告中提出的问题与“关心老人”组织在这方面正在做的工作有直接的关系。

8 rigid   

adj.严格的，死板的；刚硬的，僵硬的

参考例句：

• She became as rigid as adamant.她变得如顽石般的固执。
• The examination was so rigid that nearly all aspirants were ruled out.考试很严，几乎所有的考生都被淘汰了。

9 autonomous   

adj.自治的；独立的

参考例句：

• They proudly declared themselves part of a new autonomous province.他们自豪地宣布成为新自治省的一部分。
• This is a matter that comes within the jurisdiction of the autonomous region.这件事是属于自治区权限以内的事务。

10 physically   

adj.物质上，体格上，身体上，按自然规律

参考例句：

• He was out of sorts physically,as well as disordered mentally.他浑身不舒服，心绪也很乱。
• Every time I think about it I feel physically sick.一想起那件事我就感到极恶心。

11 asteroid   

n.小行星；海盘车(动物)

参考例句：

• Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
• It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小，但这样的危险还是存在的。

12 geographic   

adj.地理学的，地理的

参考例句：

• The city's success owes much to its geographic position. 这座城市的成功很大程度上归功于它的地理位置。 来自《简明英汉词典》
• Environmental problems pay no heed to these geographic lines. 环境问题并不理会这些地理界限。 来自英汉非文学 - 环境法 - 环境法

13 distinguished   

adj.卓越的，杰出的，著名的

参考例句：

• Elephants are distinguished from other animals by their long noses.大象以其长长的鼻子显示出与其他动物的不同。
• A banquet was given in honor of the distinguished guests.宴会是为了向贵宾们致敬而举行的。

14 tract   

n.传单，小册子，大片(土地或森林)

参考例句：

• He owns a large tract of forest.他拥有一大片森林。
• He wrote a tract on this subject.他曾对此写了一篇短文。