The landscape would have looked spectacular, comprising of deep channels around a kilometre wide, known as Tunnel Valleys. They were cut by rivers that flowed at high speeds that ran under ancient ice sheets in Northern Europe. But today, the landforms are out of view, hidden by bottom-muds in the North Sea.
Now, new scans have exposed them in spectacular 3D imaging.
This gives scientits important insight into how modern-day ice sheets like Greenland will eventually decay, according to scientists.
This is because the features were all marked during periods of great melt.
James Kirkham, from the British Antarctic Survey (BAS) and Cambridge University, said: “These tunnel valleys were formed during the death throes of an ice sheet in extremely warm climates.
“This makes them a great analogue for what Greenland, or even Antarctica, might begin to look like in the future, perhaps several 100 years down the line.
“In the way that we can leave footprints in the sand, glaciers leave an imprint on the land upon which they flow.”
If you visit Greenland today, you can find massive lakes of meltwater pooling on the surface of ice sheets during the summer.
The travels down holes to reach the bed.
From there, it spreads out and drains into the sea.
While it does this, the water also lubricates the flow of the ice sheet above.
All different kinds of sensors have been used by researchers try to understand the sub-glacial processes involved in this.
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During warm phases, the tunnel valleys got cut.
The researchers described a complex network of incisions and deposits made both by the rivers and by ice moving around on top.
BAS co-author Dr Kelly Hogan, said: “These patterns we see in the seismic data show us what the sub-glacial rivers were doing over many years, centuries even, as the ice was retreating,
“And they also show us how that ice on top was behaving. We can see where it was moving quickly or where it had simply stagnated and melted away.
“This is all information we need to properly model modern ice sheets, to try to understand what Greenland and Antarctica might look like in the future.”
The study was published in the journal Geology.