By Daniel Strain
根據科羅拉多大學波德分校的科學家發表的新研究，大約在距今10000年前末次冰期即將落幕之際，北美大陸的漂移速度以及大西洋的擴張速度可能曾經短暫提升——而融化的冰河在這其中助了一臂之力。
在此新研究當中，地球物理學家Tao
Yuan和Shijie
Zhong利用電腦模擬(模型)來回溯地球的過去至大約26000年前。當時覆蓋北美、最南到達賓州的巨大冰層——勞倫斯冰層開始消融，融化的雪水大量流進海洋，使得全世界的海面以平均每年一公分左右的速度上升。
這兩位科學家發現全球冰層融化還會造成意料之外的後果，像是對板塊運動產生影響。板塊運動猶如地球本身的發條裝置，數十億年來持續將陸地分裂開來，再讓它們碰撞結合在一起。
根據團隊的計算結果，北美大陸板塊的運動速度在冰層融化時可能加快了25%。與此同時，位於北美板塊與歐亞板塊之間的大西洋中洋脊，擴張的速度可能也增加了40%。
「冰層體積大幅減少的時候也讓地殼產生了劇烈變動，」Yuan表示。他是科羅拉多大學波德分校物理系的研究生。「科學家早就知道冰層融化會讓板塊抬升。但我們證明冰層融化也可以讓板塊產生大量水平方向的運動。」
研究人員的發現4月23日發表在期刊《自然》(Nature)。
他們的成果對於當今的地球來說可能也別具意義。覆蓋格陵蘭的冰層如今再次以相當快的速度融化，讓人意想不到的是，這可能會讓距離不遠的冰島發生更加頻繁的火山爆發。
「我們很久很久以來都是這麼說的：由地球內部的引擎，也就是熱對流作用所驅動的海底擴張與大陸漂移，是以百萬年的時間尺度來進行，」同校的物理教授Zhong表示。「這當然沒有錯，但我們顯示冰河的力量也可以在10000年這種相對短的時間尺度當中，就讓板塊出現顯著的運動。」
動力來源
此研究的經費來源為美國國家科學基金會。研究人員深入探討了大西洋中洋脊，這道位於大西洋中央的地形特徵綿延了數千公里，途中還切過了冰島。中洋脊是個動盪不安的場所：從地球深處湧上來的岩漿會從這裡冒出地殼，冷卻之後形成岩石，促使北美大陸與歐洲遠離彼此。
數個世代的科學家都認為這道過程大致上是穩定的——過去數百萬年以來大西洋中洋脊的擴張速率應該都保持在每年2公分左右。
「這是個眾所皆知寫在教科書上的數字，」Zhong表示。
但教科書是否寫錯了？
為了找出答案，Zhong和Yuan利用電腦模型重現距今數萬年前的地球。他們模擬了曾經覆蓋在現今的加拿大與格陵蘭、厚達數公里的冰河融化的時候，由於其重量從陸地轉移到海洋所造成的結果。
把地球想像成一塊記憶床墊會簡單一些。當躺在記憶床墊上的人起身之後，裡面的泡棉會慢慢回彈至原本的形狀。Zhong和Yuan說冰層融化之後地球也會發生類似的現象。
隨著勞倫斯冰層的重量重新分配到全世界的海洋，北美洲的一部分也開始往上回彈(現在加拿大哈德遜灣周圍的陸地仍因為此力道，而以每年1公分左右的速度抬升)。不只如此，根據這篇新研究，勞倫斯冰層融化可能也影響了北美洲以及大西洋中洋脊的水平運動。
火山爆發
Zhong和Yuan表示冰層融化可能也對距離格陵蘭不遠的冰島造成猛烈的影響。
比方說，地質證據透露冰島在冰河期末曾有一段時期火山活動相當強烈，之後才漸漸和緩下來。格陵蘭冰層融化造成大西洋中洋脊的擴張速度增加，或許導致了這段熾熱的過往時光。此現象可以讓更多岩漿上升到地表，為火山與間歇泉噴發增添更多燃料。
「冰島的火山活動會有這種模式，一部分的原因可能就是我們所研究的冰河融化，」Zhong表示。
今日覆蓋格陵蘭的冰層融化速度還沒有快到能對地球的大陸漂移造成衝擊。但在未來數百年它仍然有機會對冰島產生顯著的影響，尤其是冰河的消失速度持續上升的話。
「格陵蘭與南極西部的冰層仍在持續融化，」Yuan表示。「我們認為冰層融化未來會提升附近中洋脊的海底擴張速度，並讓該處的火山活動變得更加劇烈。」
Melting glaciers
at the end of the Ice Age may have sped up continental drift, fueled volcanic
eruptions
Around 10,000 years ago as the last Ice
Age drew to a close, the drifting of the continent of North America, and
spreading in the Atlantic Ocean, may have temporarily sped up—with a little
help from melting glaciers, according to a new study from scientists at the University
of Colorado Boulder.
In the new research, geophysicists Tao Yuan and
Shijie Zhong used computer simulations, or models, to travel back roughly 26,000
years into the planet’s past. At the time, the massive Laurentide Ice Sheet,
which stretched over North America as far south as Pennsylvania, started to
recede. Melting ice flooded into the oceans, and sea levels worldwide rose by
an average of around 1 centimeter per year.
The scientists discovered that this global thaw may
have also had unexpected consequences—including for plate tectonics, or the
internal clockwork that has, for billions of years, torn Earth’s continents
apart and crushed them together.
According to the team’s calculations, the motion of
the North American continental plate may have sped up by 25% as the ice melted.
At the same time, spreading at the Mid-Atlantic Ocean Ridge, which sits between
the North American and Eurasian plates, may have increased by as much as 40%.
“As ice volume was greatly reduced, it caused a huge
motion in Earth’s crust,” said Yuan, a graduate student in the Department of
Physics at CU Boulder. “Scientists knew that the ice melting caused the plates
to uplift. But we show that they also moved a lot horizontally due to the ice
melting.”
The researchers published their findings April 23 in
the journal Nature.
Their results may have implications for the planet
today. Ice sheets over Greenland are once again melting at a rapid rate, which,
in a strange twist, could drive an increase in volcanic eruptions in Iceland
not far away.
“That story that we’ve been telling for a long, long
time—that processes like seafloor spreading and continental drift operate at
timescales of millions of years driven by Earth’s internal engine—thermal
convection,” said Zhong, a professor of physics. “That’s still true, but we
show that glacial forcing can also cause significant motion on relatively short
timescales of 10,000 years.”
Moving gears
The research, which was funded by the U.S. National
Science Foundation, takes a deep dive into the Mid-Atlantic Ocean Ridge. This
feature runs for thousands of miles down the center of the Atlantic Ocean and
cuts through the island of Iceland. It’s a turbulent place: There, magma from
deep within the planet bubbles up through the crust, cooling into solid rock
and helping to force the continents of North America and Europe away from each
other.
For generations, scientists believed that this
process was largely steady—with the ridge spreading by a consistent 2
centimeters every year for the past several million years.
“That’s a fairly well-known, textbook number,” Zhong
said.
But could the textbooks be wrong?
To find out, Zhong and Yuan used computer models to
recreate the Earth as it was thousands of years ago. The researchers simulated
what might happen as glaciers that were kilometers thick disappeared from
modern-day Canada and Greenland—shifting that weight off dry land and into the
ocean.
It helps to picture the globe as a memory foam
mattress. If you’re lying on a mattress and get up, the foam will slowly bounce
back to its original shape. Something similar happened on Earth as ice sheets
melt, Zhong and Yuan said.
As the weight of the Laurentide Ice Sheet was
redistributed around the planet, parts of North America began to bounce back
up. (Today, land around Canada’s Hudson Bay is still rising by around 1 centimeter
per year because of that rebound). According to the new study, the melting may
have also affected the horizontal motion of North America and the Mid-Atlantic
Ocean Ridge.
Volcanic
eruptions
The thaw may also have had explosive consequences for
Iceland, which sits close to Greenland, Yuan and Zhong said.
Geological evidence, for example, suggests that the
island underwent a period of intense volcanic activity at the end of the last
Ice Age, which has since quieted down. Enhanced spreading at the Mid-Atlantic
Ocean Ridge due to ice melting from Greenland may have contributed to that
fiery past—allowing more magma to rise to the surface, fueling the eruption of
volcanoes and geysers.
“This pattern of volcanism may have been partly due
to the glacial melting that we studied,” Zhong said.
Today, ice over Greenland isn’t melting fast enough
to have much of an impact on the planet’s continental drift. But it could still
have a major influence on Iceland over the next several hundred years,
especially if glaciers begin to disappear at an accelerating rate.
“Ice sheets in Greenland and West Antarctica are
still melting,” Yuan said. “We think the ice melting could enhance seafloor
spreading and volcanism at nearby mid-ocean ridges in the future.”
原始論文：Tao Yuan, Shijie
Zhong. Effects of glacial forcing on lithospheric motion and ridge
spreading. Nature, 2025; DOI: 10.1038/s41586-025-08846-x
引用自：University of Colorado at Boulder.
"Melting glaciers at the end of the Ice Age may have sped up continental
drift, fueled volcanic eruptions."
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