The ancient ice sheets that covered the UK and Europe expelled water to stop themselves from collapsing.
The research team was surprised by the discovery that the valleys took just hundreds of years to form.
The new understanding of when the ice sheets melted 20,000 years ago has implications for how glaciers respond to climate change today. There is a study in the journal.
The tunnel valleys are large channels that drain water from underneath the ice sheets. Over the last two million years, the melting of ice sheets has covered the UK and Western Europe.
James Kirkham is the lead author of the book. During the death throes of ice sheets, these valleys are carved out. By using a combination of state-of-the-art techniques and a computer model, we have learned that tunnel valleys can be eroded quickly under ice sheets.
3D scans of the Earth's buried layers are provided by the team. As the last ice sheet to cover the UK melted away at the end of the most recent ice age about 20,000 years ago, the authors performed a series of computer modeling experiments to mimic valley development and test how quickly they formed.
The research shows that the process of melting ice forms giant tunnel valleys within hundreds of years, expelling water that could speed up ice loss.
The drainage of water from beneath ice sheets is thought to be a way to keep ice sheets from collapsing in a warming climate. The authors found tell-tale signatures of both stagnant and rapid ice movement, complicating the picture of how these rapidly forming channels might affect future ice sheet behavior.
What is certain is that the fast rate at which these tunnels form means that scientists need to start considering their effects in models of how ice sheets will evolve in the future.
These ancient valleys, buried hundreds of meters beneath the muds of the North Sea, record a mechanism for how ice sheets respond to extreme warmth that is missing from today's models. The models do not currently resolve fine-scale water drainage processes, even though they appear to be an important control on future ice loss rates.
The pace at which these giant channels can form means that they are an important, yet currently ignored, mechanism that could potentially help to stabilizing ice sheets in a warming world. As climate change continues to drive the retreat of the modern-day Greenland and Antarctic ice sheets at ever increasing rates, our results call for renewed investigation of how tunnel valleys may help to stabilizing contemporary ice losses, and thus sea level rise, if they switch on beneath the Earth's ice sheets
The huge meltwater channels from areas covered by ice sheets have been observed for more than a century but we did not really understand how they formed.
The process of water transport through the system will only increase as our climate warms. Will the extra meltwater flow in channels cause our ice sheets to flow more quickly or slower into the sea?
The work shows a process that can quickly switch on under ice sheets. The question of whether these channels will help or hurt the Earth's ice sheets in a warming world is an open one.
More information: Chris D. Clark et al, Growth and retreat of the last British–Irish Ice Sheet, 31 000 to 15 000 years ago: the BRITICE‐CHRONO reconstruction, Boreas (2022). DOI: 10.1111/bor.12594 Journal information: Quaternary Science Reviews
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