格陵兰岛的冰原曾短暂地形成了世界上最高的瀑布

格陵兰岛的冰原曾短暂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，在委内瑞拉卡奈玛国家公园上空979米(3212英尺)的天使瀑布一度被认为是世界上最高的瀑布。据剑桥大学的研究人员称，“篡位者”是一个巨大的裂缝，位于数千英里外格陵兰冰原的一个融水表面湖的下方。大约500万立方米(13亿加仑)的水——大约相当于2000个奥运会标准大小的游泳池——直冲到下面的基岩，短短5个小时就把湖面面积缩小到原来的三分之一。

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经常会发生灾难性的裂缝，并迅速通过被称为“莫林”的空洞排出，迄今为止，科学家们一直依靠卫星数据来记录这一过程。这次不同。在现场进行研究时，剑桥大学的研究小组能够使用专门设计的无人机实时记录快速排水。

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)."

通过在冰层上安装传感器和多次无人机飞行，研究人员能够追踪流经裂缝和地表下的水流。在一篇发表在美国国家科学院院刊上的论文中,他们解释表面水的大量涌入造成“冰流加速从每天两米的速度超过5米/天地表水被转移到床上,从而解除了冰盖半米(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.

与英国阿伯里斯特威斯大学和兰开斯特大学的研究人员合作，该团队能够将数据重建成3D模型，以显示融水排水如何影响新裂缝的形成和休眠裂缝的扩展。它还支持剑桥大学科学家提出的一个计算机模型，该模型认为，这样的湖泊排水是在剧烈的连锁反应中发生的。

"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."

“我们可能低估了这些冰川对格陵兰冰盖整体不稳定性的影响，”该研究小组的无人机驾驶员、剑桥大学博士生汤姆·查德利在一份声明中说。“真正观察这些快速流失的湖泊是一件罕见的事情——我们很幸运，在正确的时间出现在正确的地方。”

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.

由于格陵兰冰盖是造成全球海平面上升的最大单一因素，研究小组将继续研究，随着气候继续变暖，这些排水事件将如何加速其下降。他们的下一步是使用钻井设备，直接观察冰下排水系统如何容纳大量的表面融水。

"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告诉《科学美国人》:“在过去的30年里，格陵兰冰原确实发生了巨大的变化。”“我们需要了解正在发生的过程。”