While Iceland’s largest glacial ice sheets continue to melt at increasing rates, a UA-led research team has determined that the ground on which Iceland sits is rising — almost 1.4 inches a year in some places.
“In Iceland, what we’ve shown is this direct connection between how fast the glaciers are melting and how fast the Earth comes up,” said Kathleen Compton, a geosciences graduate student.
The process of large amounts of ice melting and subsequent rising of the ground is known as post-glacial rebound. The melting of large ice sheets and resultant uplift of the Earth can have far reaching consequences and potentially affect volcanoes, which Iceland has more than a hundred of.
“If we look back in the geologic record, back in time to Iceland, to about [10,000 or 12,000] years ago, what we see is that there was a transition from ice age to interglacial,” Compton said. “What we saw is that, as the ice was melting away, there was a peak in volcanic activity. In some places in Iceland, the volume of erupted material is, like, 30 times larger than normal rates that we would see today.”
In the presence of glaciers, the rock deep below the ground is under high temperature and pressure. Lightening the load on the rock by melting the ice on top of it causes the ground to rise, thus lowering the pressure. If this happens fast enough, the rock will not have time to release the heat conductively and will instead melt, explained Richard Bennett, a geosciences associate professor.
“There’s all kinds of ways to think about the implications of melting ice,” Bennett said. “You’re also increasing sea levels, for example. Having glaciers sitting on top of volcanic systems is inherently dangerous because the volcanoes themselves can melt the ice, and melt it on a very short time scale, which creates what is called a ‘jökulhlaup,’ or a sudden flood of water from a glacier, which can devastate any nearby population centers.”
The study was prompted when the scientists noticed an acceleration signal at a particular station on Iceland, and they wanted to see if this was occurring at other stations across the island as well, Bennett said.
“Geoscientists have known for a long time that the weight of large sheets of ice, like those in Iceland, is so much that it pushes the surface of the Earth down,” Compton said. “A good way to think about is someone standing on a trampoline — the weight of their body will make the trampoline sag under them, and then if they hop off the trampoline, that surface regains its original shape —–— or rebounds upward.”
The island of Iceland presents researchers with an opportunity to study glacial rebound more effectively than in other areas of the world.
“Iceland is unique in that you can think of it as not being contaminated by ‘half-signals’ of glaciation or deglaciation from previous ice ages,” Compton said. “Iceland behaves a lot more like a trampoline than a memory foam mattress in terms of rebound.”
Even though areas of North America — especially Canada — Sweden and Finland were also covered in large ice sheets during the previous ice age, the ground in these areas is still rebounding from the melting of all that ice, Bennett said. In Iceland, that rebounding has already completed.
“What we’re looking at [in Iceland] is uplift that is connected to modern-day climate change,” Compton said.
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