Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists explain formation of stone circles and other strange patterns in northern regions

17.01.2003


Mysterious patterns arise through simple feedback mechanisms and self-organization



Perfect circles of stones cover the ground in parts of Alaska and the Norwegian islands of Spitsbergen. Elsewhere in the far north, stones form other striking patterns on the ground: polygons, stripes, islands, and labyrinths. No, pranksters are not at work in these remote areas, nor are aliens, elves, or any other outside forces moving the stones around. According to scientists who have studied the phenomenon, cyclic freezing and thawing of the ground drives simple feedback mechanisms that generate these remarkable patterns.

"The patterns form by self-organization, and the same fundamental processes are at work in the formation of all these different patterns," said Mark Kessler, a postdoctoral researcher in the Earth Sciences Department at the University of California, Santa Cruz.


As a graduate student working with Brad Werner, a professor of geophysics at UC San Diego, Kessler developed a numerical model of the processes involved in the self-organization of these patterns, known to geologists as "sorted patterned ground." Kessler and Werner reported their findings in a paper published in the January 17 issue of the journal Science.

Over the years, other scientists have proposed various explanations for these unusual patterns of stones and soil. But until now, no single explanation has been able to account for the full range of patterns seen in nature.

"The model I developed is essentially a hypothesis about what is important in the formation of patterned ground," Kessler said. "When you run the model on a computer, you can see the evolution of the pattern over time, and you can also see how small changes in key parameters result in a transition from one pattern to another."

According to Kessler, the patterns result primarily from the interaction of two mechanisms: lateral sorting, which moves soil toward areas of high soil concentration and stones toward areas of high stone concentration; and squeezing of stone domains, which causes stones to move within linear piles of stones and lengthens these lines of stones. The relative strengths of lateral sorting and squeezing, plus the slope of the ground and the ratio of stones to soil, are the factors that determine which pattern will emerge, Kessler said.

Driving the mechanisms of lateral sorting and squeezing is the phenomenon of frost heave--the expansion of fine-grained soils during freezing of wet ground. Frost heave results from the formation of discrete ice lenses in the soil. The soil near the surface expands because water flows up through the soil toward the ice lens as it forms (and to a lesser extent because the water expands as it freezes).

"If you start with a random layer of stones over a layer of soil, frost heave makes the soil layer unstable and deforms the interface between stones and soil," Kessler said.

As an ice lens grows near this interface, it pushes outward on the stones and also dessicates and compresses the soil below it. Where the interface between stones and soil is inclined, this causes lateral displacement of both stones and soil. When the ground thaws, the compressed soil reabsorbs water and expands. But the expansion occurs vertically, so it does not reverse the lateral displacement of soil by frost heave. Furthermore, the greater compressibility of soil-rich areas results in soil transport toward those areas.

Other processes are also involved in lateral sorting, but the end result is a positive feedback loop in which cycles of freezing and thawing cause soil-rich areas to attract more soil and stone-rich areas to attract more stones.

Once stones have been sorted into concentrated areas, or "stone domains," frost heave also squeezes and uplifts the stone domains. Differential uplift causes stones to migrate along the axis of a linear stone domain and lengthens the domain.

"The pattern depends on the relative strengths of lateral sorting, which actually brings stones back into areas of high stone concentration, and squeezing, which moves stones along," Kessler said. "One of the real mysteries to me was how you can get labyrinths or islands of stones in one location and polygons in another, when the ratio of stones to soil is the same in both places. Our model indicates that you get polygons when the squeezing is strong enough to counteract the effects of lateral sorting."

There are a variety of factors that can lead to differences in the relative strengths of squeezing and lateral sorting, he said. These include the compressibility of the soil and the size of the stones.

Another important factor is the extent to which the stone domains are confined by the soil, which determines whether squeezing will mainly cause stones to move along the stone domains or roll back onto the soil domains. In their model, Kessler and Werner can vary the degree of confinement, the concentration of stones, and the slope of the ground to produce circles, labyrinths, islands, stripes, and polygons of stones.

The researchers compared the patterns generated by the model with those observed in nature, using low-elevation aerial photographs of polygon networks in Alaska. Quantitative measurements of the natural and computer-generated polygons showed they were consistent. For example, one of the interesting features of polygon patterns, both in the model and in nature, is the tendency to form three-way intersections with equal angles between the intersecting lines, Kessler said.

One reason these patterns have remained unexplained for so long may be their occurence in remote areas, far from the temperate zone where most scientists live, Kessler said. "If these patterns were on the ground around here, I think we would have figured them out a long time ago. These landscapes are so amazing, it’s the kind of thing that really calls out for an explanation."

Tim Stephens | EurekAlert!
Further information:
http://www.ucsc.edu/

More articles from Earth Sciences:

nachricht GPM sees deadly tornadic storms moving through US Southeast
01.12.2016 | NASA/Goddard Space Flight Center

nachricht Cyclic change within magma reservoirs significantly affects the explosivity of volcanic eruptions
30.11.2016 | Johannes Gutenberg-Universität Mainz

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>