Melting ice can speed up continental drift and fuel volcanic eruptions

When we picture tectonic plates drifting apart and colliding, we usually imagine a time-lapse spanning millions of years. However, a new study reveals melting ice can affect continental drift and volcanic activity.

Research from the University of Colorado Boulder indicates that Earth’s crust can feel a substantial jolt on a far shorter timetable – thousands of years – whenever colossal ice sheets melt away. Geophysicists Tao Yuan and Shijie Zhong traced events that began roughly 26,000 years ago, near the peak of the last Ice Age.

Back then, the Laurentide Ice Sheet blanketed much of North America in layers of ice several kilometers thick, stretching south to what is now Pennsylvania. As global temperatures warmed, that icy behemoth dwindled.

Meltwater poured into the oceans, lifting sea levels by roughly a centimeter per year. Yet the scientists found that the consequences went well beyond rising coastlines: they extended deep into the mechanics of plate tectonics.

Melting ice and continental drift

“As ice volume was greatly reduced, it caused a huge motion in Earth’s crust,” said Yuan, a doctoral candidate in CU Boulder’s Department of Physics and lead author of the study. “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.”

Yuan and Zhong’s models indicate that between about 12,000 and 6,000 years ago, the North American plate may have increased its overall drift speed by roughly 25 percent.

Even more striking was the behavior of the Mid-Atlantic Ridge. This ridge is a submarine mountain chain where magma wells up to form new crust and push the North American and Eurasian plates apart. There, seafloor spreading may have surged by as much as 40 percent during the post-glacial interval.

Zhong, a professor of physics at CU Boulder and senior author on the study, elaborated on the significance of the findings.

“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. That’s still true, but we show that glacial forcing can also cause significant motion on relatively short timescales of 10,000 years,” said Zhong.

Melting ice messes with the mantle

To understand this surprising connection, picture Earth’s lithosphere – the rigid outer shell comprising crust and upper mantle – as a giant memory-foam mattress. When you lie on memory foam, the surface depresses; when you get up, it slowly rebounds.

Similarly, when an ice sheet thousands of meters thick presses down on a continent, the underlying mantle deforms. Once that ice melts and its weight shifts to the oceans, the mantle rebounds upward. Geologists call this response “glacial isostatic adjustment.”

Vertical rebound is well documented: regions near Hudson Bay, once the epicenter of glacial weight, still rise by about a centimeter per year. What Yuan and Zhong uncovered is a lesser-known horizontal component.

As the mantle flowed to readjust, it exerted lateral stresses that nudged tectonic plates, effectively giving them a temporary shove. Their models show that this nudge affected both continental interiors and mid-ocean ridges.

The Mid-Atlantic Ridge is a critical test case because geologists have long treated its two-centimeter-per-year spreading rate as a textbook constant. The CU Boulder simulations suggest that rate has actually fluctuated markedly, speeding up in tandem with glacial retreat.

A volcanic echo in Iceland

One real-world clue supporting the model’s conclusions lies in Iceland, which straddles the Mid-Atlantic Ridge just south of Greenland. Geological evidence indicates a spike in volcanic and geothermal activity on the island as the last Ice Age waned.

Zhong believes faster spreading beneath the ridge made it easier for magma to reach the surface, fueling Iceland’s fiery outbursts. “This pattern of volcanism may have been partly due to the glacial melting that we studied,” Zhong noted.

Although Greenland’s ice is melting rapidly today, its present rate is not yet large enough to jolt continents around. However, many climate models predict accelerated ice melting which could once again modulate magma supply at nearby ridges and, indirectly, volcanic activity in places such as Iceland within the next several centuries.

“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.”

Will melting ice accelerate continental drift?

The implications of the study reach beyond Iceland or any single ridge. If glacial cycles can tweak plate speeds, geologists may need to revisit other intervals in Earth’s history when ice ages ended abruptly.

Could bursts of continental acceleration have left signatures in mountain-building episodes or sediment records? Might similar dynamics occur under today’s rapidly melting Antarctic ice shelves, subtly influencing tectonics in the Southern Ocean?

Zhong and Yuan’s results remind scientists that tectonics and climate are not wholly separate realms. The deep interior drives plate motion, but surface processes – especially the waxing and waning of planetary ice – can modulate that motion on geologically brief timescales.

The Earth, in other words, is a tightly coupled system: what disappears atop a continent can ripple beneath an ocean ridge thousands of kilometers away. “That’s a fairly well-known, textbook number,” Zhong said of the ridge’s 2 cm/year spreading pace. He noted that the textbook may need an update.

Funded by the U.S. National Science Foundation, this research highlights a key point for both geologists and climate scientists: the planet’s frozen water doesn’t just sculpt landscapes; it can also tweak the gears of Earth’s tectonic machinery. And as the modern cryosphere continues to shrink, understanding such connections becomes ever more vital.

The study is published in the journal Nature.

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