Strange, regularly repeating stone patterns that sometimes form in cold settings are generated by needles of ice that push soil particles and stones slowly around.
This is the conclusion of an international team of researchers who used lab experiments and computer modelling to study how the striking features form.
Over the course of years and numerous freeze–thaw cycles, the ice needles gradually nudge any stones around until they clump together, forming patterns.
The shape of these patterns depends on factors including the concentration of stones, the size of the ice needles and the slope of the groundl, according to the team.
For example, more linear features form when ice needles are created on a slope.
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Strange, regularly repeating stone patterns that sometimes form in cold settings are generated by needles of ice that push soil particles and stones slowly around. Pictured: complex ground patterns in Svalbard, Norway, resemble a labyrinth
Needle ice forms when the temperature drops and moisture contained in the soil grows into thin spikes of ice crystals that protrude from the ground, pushing soil as they do (as shown)
Patterned ground is often seen in polar regions, on high mountains, and in other chilly environments, explains paper author Bernard Hallet, who specialises in investigating patterns in nature.
‘The presence of these amazing patterns that develop without any intervention from humans is pretty striking,’ the University of Washington earth scientist added.
‘It’s like a Japanese garden — but where is the gardener?’
According to Professor Hallet, needle ice forms when the air temperature drops below freezing and moisture contained in the soil grows into thin spikes of ice crystals that can protrude up and out from the ground.
‘When you go out in the backyard after a freezing night and you feel a little crunch under the foot, you’re probably walking on needle ice,’ he added.
As the icy needles form, they tend to push up soil particles and any small stones.
Alongside this, Professor Hallet explained, needle ice forms more readily on patches of bare soil in comparison with rock-covered areas.
Put together, these two properties cause the icy growth to slowly displace any remaining stones out of barer regions — and, over the course of years a numerous frosts, this leads the stones to cluster together with totally bare patches in-between.
‘That kind of selective growth involves interesting feedbacks between the size of the stones, the moisture in the soil and the ice needles’ growth,’ said Professor Hallet.
Patterned ground is often seen in polar regions, on high mountains, and in other chilly environments, explains paper author Bernard Hallet, who specialises in investigating patterns in nature. Pictured: an example of patterned ground in Svalbard, Norway. Each circle is around 10 feet (3 metres) in diameter
In their study, the researchers conducted an experiment with a flat square of wet soil — one just over 1 foot (0.4 metres) on each side — onto which they had uniformly spaced out small stones.
The team then froze and thawed the soil 30 times over, observing how the formation of needle ice gently pushed the stones around as they did so.
By the end of the test, the team found that regular patterns had begun to appear in the distribution of the rocks.
In other tests, the researchers explored how the patterns produced changed when they started with a different concentration of stones or when the soil sloped.
They also looked at the impact of the height of the ice needles – a factor which is also affected by the stone concentration.
From their observations, the team were able to develop computer model that can predict what pattern of stones will appear based on the starting stone concentration and ground slope
From their observations, the team were able to develop computer model that can predict what pattern of stones will appear based on the starting stone concentration and ground slope.
‘The videos are pretty striking and they show that the ice just comes up and in a single cycle it pushes up stones and moves them slightly to the side,’ explained Professor Hallet.
‘Because of those experiments […] we have much more tangible, quantitative descriptions of these features.’
The full findings of the study were published in the journal Proceedings of the National Academy of Sciences.
‘The presence of these amazing patterns that develop without any intervention from humans is pretty striking,’ Professor Hallet concluded. Pictured: when ice needles form on sloping ground, then form linear features — as seen in this photograph of Hawaii