格陵蘭島的冰原曾短暫地形成了世界上最高的瀑布

格陵蘭島的冰原曾短暫地形成了世界上最高的瀑布

For a brief moment last year, Angel Falls — looming 979 meters (3,212 feet) over Canaima National Park in Venezuela — was likely dethroned as the world's tallest waterfall. The usurper, according to researchers from the University of Cambridge, was a massive fracture that opened underneath a meltwater surface lake thousands of miles away on the Greenland ice sheet. About 5 million cubic meters (1.3 billion gallons) of water — roughly equivalent to 2,000 Olympic-sized swimming pools — plunged straight down to the bedrock below, reducing the lake's area to a third of its original size in as little as five hours.

去年，在委內(nèi)瑞拉卡奈瑪國(guó)家公園上空979米(3212英尺)的天使瀑布一度被認(rèn)為是世界上最高的瀑布。據(jù)劍橋大學(xué)的研究人員稱(chēng)，“篡位者”是一個(gè)巨大的裂縫，位于數(shù)千英里外格陵蘭冰原的一個(gè)融水表面湖的下方。大約500萬(wàn)立方米(13億加侖)的水——大約相當(dāng)于2000個(gè)奧運(yùn)會(huì)標(biāo)準(zhǔn)大小的游泳池——直沖到下面的基巖，短短5個(gè)小時(shí)就把湖面面積縮小到原來(lái)的三分之一。

Researchers from the University of Cambridge inspect a massive fracture in the Greenland ice sheet. That fracture helped quickly drain a large meltwater lake in 2018. (Photo: Sarah Collins/Cambridge University)

It's common for meltwater lakes residing on ice sheets to experience catastrophic fractures and quickly drain through cavities known as moulins, but to date, scientists have relied on satellite data to document the process. This time was different. While on site conducting research, the University of Cambridge team was able to record the swift drainage in real time using specially designed drones.

居住在冰原上的融水湖經(jīng)常會(huì)發(fā)生災(zāi)難性的裂縫，并迅速通過(guò)被稱(chēng)為“莫林”的空洞排出，迄今為止，科學(xué)家們一直依靠衛(wèi)星數(shù)據(jù)來(lái)記錄這一過(guò)程。這次不同。在現(xiàn)場(chǎng)進(jìn)行研究時(shí)，劍橋大學(xué)的研究小組能夠使用專(zhuān)門(mén)設(shè)計(jì)的無(wú)人機(jī)實(shí)時(shí)記錄快速排水。

Drone imagery captured the lake drainage in unprecedented detail. The image on the left was taken at ~13:00. About 5 hours later, the lake started to drain, and by 02:00 (right), it had lost two thirds of its volume. The main fracture responsible for the drainage can be seen near the bottom of the image. (Photo: Sarah Collins/Cambridge University)

Using sensors in the ice and multiple drone flights, the researchers were able to track the flow of water as it drained through the fracture and under the surface. In a paper published in Proceedings of the National Academy of Sciences, they explain how the massive influx of surface water caused "the ice flow to accelerate from a speed of two meters per day to more than five meters per day as surface water was transferred to the bed, which in turn lifted the ice sheet by half a meter (1.5 feet)."

通過(guò)在冰層上安裝傳感器和多次無(wú)人機(jī)飛行，研究人員能夠追蹤流經(jīng)裂縫和地表下的水流。在一篇發(fā)表在美國(guó)國(guó)家科學(xué)院院刊上的論文中,他們解釋表面水的大量涌入造成“冰流加速?gòu)拿刻靸擅椎乃俣瘸^(guò)5米/天地表水被轉(zhuǎn)移到床上,從而解除了冰蓋半米(1.5英尺)。”

Moulins like this one, often plunging more than 3,000 feet to the bedrock below, are responsible for quickly draining massive surface lakes on the ice sheet. (Photo: Sarah Collins/Cambridge University)

In partnership with researchers from Aberystwyth and Lancaster universities in the United Kingdom, the team was able to reconstruct the data into 3D models to show how meltwater drainage influences the formation of new fractures and the expansion of dormant ones. It also supports a computer model proposed by the Cambridge scientists that such lake drainages occur in a dramatic chain reaction.

與英國(guó)阿伯里斯特威斯大學(xué)和蘭開(kāi)斯特大學(xué)的研究人員合作，該團(tuán)隊(duì)能夠?qū)?shù)據(jù)重建成3D模型，以顯示融水排水如何影響新裂縫的形成和休眠裂縫的擴(kuò)展。它還支持劍橋大學(xué)科學(xué)家提出的一個(gè)計(jì)算機(jī)模型，該模型認(rèn)為，這樣的湖泊排水是在劇烈的連鎖反應(yīng)中發(fā)生的。

"It's possible we've under-estimated the effects of these glaciers on the overall instability of the Greenland Ice Sheet," co-first author Tom Chudley, a Ph.D. student at the University of Cambridge and the team's drone pilot, said in a statement. "It's a rare thing to actually observe these fast-draining lakes — we were lucky to be in the right place at the right time."

“我們可能低估了這些冰川對(duì)格陵蘭冰蓋整體不穩(wěn)定性的影響，”該研究小組的無(wú)人機(jī)駕駛員、劍橋大學(xué)博士生湯姆·查德利在一份聲明中說(shuō)。“真正觀察這些快速流失的湖泊是一件罕見(jiàn)的事情——我們很幸運(yùn)，在正確的時(shí)間出現(xiàn)在正確的地方。”

Researchers flew drones over the lake as it was draining, building 3D models of the ice sheet surface as well as capturing spectacular images of waterfalls entering the depths of the ice sheet. (Photo: Tom Chudley/Cambridge University)

As the Greenland ice sheet is the single largest contributor to global sea-level rise, the research team will continue studying how these drainage events might hasten its decline as the climate continues to warm. Their next step is to use drilling equipment to observe first-hand how mass quantities of surface meltwater is accommodated in the subglacial drainage system.

由于格陵蘭冰蓋是造成全球海平面上升的最大單一因素，研究小組將繼續(xù)研究，隨著氣候繼續(xù)變暖，這些排水事件將如何加速其下降。他們的下一步是使用鉆井設(shè)備，直接觀察冰下排水系統(tǒng)如何容納大量的表面融水。

"The Greenland ice sheet has really dramatically changed over the last 30 years," Chudley told Scientific American. "And we need to understand the processes that are going on."

Chudley告訴《科學(xué)美國(guó)人》:“在過(guò)去的30年里，格陵蘭冰原確實(shí)發(fā)生了巨大的變化。”“我們需要了解正在發(fā)生的過(guò)程。”