Computer model solves the riddle of why lava sometimes forms into hexagons

October 14, 2015 by Bob Yirka report
Computer model solves the riddle of why lava sometimes forms into hexagons
Credit: Physics/iStockphoto.com/Macsnap

(Phys.org)—A team of researchers with Dresden University of Technology in Germany has apparently solved the riddle of why lava sometimes forms into hexagonal towers as it cools. In their paper published in Physical Review Letters, the team describes how they put together a computer model that ultimately showed how such shapes can form.

Scientists and other people have been amused, piqued and inspired by some of the geometric shapes that come about as cools—Devils Tower in Wyoming, for example, or Giant's Causeway in Northern Ireland, both feature cooled lava in the form of hexagonal structures. Upon seeing them, most wonder how they could have come about—after all, most things in nature are random, or perhaps round. Hexagons seem like they could come about only due to intervention by us humans. Now it appears, the team in Germany has cracked the riddle of how nature could have made it happen.

It is all about heat differential and the way cracks form, the team reports. They made these discoveries by building a model very similar to those used by engineers to build bridges or aircraft parts. It allowed them to account for the characteristics of the lava, both when it was hot, and as it cooled. That allowed them to see that after some bit of lava stopped flowing, as it cooled, the inner parts cooled faster than the outer parts, leading to shrinkage and the formation of cracks adjacent to one another, which meant they formed at 90 degree angles. Then as the lava cooled even more and more shrinkage occurred, the cracks made their way down into the lava below which was still solidifying—that forced the cracks to grow larger, forcing the angle between them to change to approximately 120 degrees, which occurred because it was the point at which the largest amount of energy was released—and it is also, of course, the same angle degree found in hexagonal structures.

The were then maintained as the lava cooled down to and the shape was persevered—meanwhile, the same process occurred around it, causing the creation of other that looked very nearly just like it.

Explore further: How a change in slope affects lava flows

More information: Why Hexagonal Basalt Columns? Phys. Rev. Lett. 115, 154301 – Published 7 October 2015. dx.doi.org/10.1103/PhysRevLett.115.154301

ABSTRACT
Basalt columns with their preferably hexagonal cross sections are a fascinating example of pattern formation by crack propagation. Junctions of three propagating crack faces rearrange such that the initial right angles between them tend to approach 120°, which enables the cracks to form a pattern of regular hexagons. To promote understanding of the path on which the ideal configuration can be reached, two periodically repeatable models are presented here involving linear elastic fracture mechanics and applying the principle of maximum energy release rate. They describe the evolution of the crack pattern as a transition from rectangular start configuration to the hexagonal pattern. This is done analytically and by means of three-dimensional finite element simulation. The latter technique reproduces the curved crack path involved in this transition.

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Returners
2.3 / 5 (15) Oct 14, 2015
See? I rest my case.

This has already been known for decades. This is freaking Geology 101.

Why the hell is a "team of researchers" spending grant money for studying a phenomenon that is already well known and documented for decades and even centuries?

More tax dollars at work.

They may as well watch grass grow, or count cow farts.
RichManJoe
4.1 / 5 (9) Oct 14, 2015
This is interesting work - I have often seen columnar basalt in Oregon, and basically understood how it could form, but developing a structural model takes it to the next step.

It would have been nice to have a video clip along with the article. The modeling tool should have generated one - we always got them from a satellite models.
johnhew
1.8 / 5 (5) Oct 14, 2015
nah, must just be a compromise between the push for circular nearest-distance evaporation centers and the push for straight-line interfaces with packing. squares lose on the first criteria. probably the same thing in insect eyes
johnhew
3.5 / 5 (4) Oct 14, 2015
but yeah,RichManJoe, a video would seem to be the whole point. I think there is sometime to the three-way junction being much more likely then likley unstable 4-way corner junctions as one would have in squares. from there the 3way junctions may migrate, anneal, and sort themselves into the regular tesslation.
docile
Oct 14, 2015
This comment has been removed by a moderator.
24volts
5 / 5 (1) Oct 14, 2015
Since when did something cool faster on the inside than the outside? That doesn't make any sense at all to me. I've never heard of the inside of some substance cooling faster than the outside when all that is at work is the heat radiating away into the atmosphere or water or dirt for that matter.
skills4u
4.2 / 5 (5) Oct 14, 2015
That is because you are picturing the event happening at once. Lave does not always flow like water with a constant velocity.It can come in spurts allowing enough time for the pooled lava to develop a cooled shell which in itself becomes a heat shield to the inner layer as new hot lava is being added to the outside.Once the lava flow does stop, the outer layer cools down faster than the time it would take for the heat of the outer layer to penetrate the inner layer. So at some point the outer layer will be cooler than the inner layer, but after the above mentioned process occurs.
SteveGinGTO
1 / 5 (4) Oct 15, 2015
@24volts: "Since when did something cool faster on the inside than the outside? That doesn't make any sense at all to me."

Exactly. This is silly stuff. In addition, since when is a model actually reality? A model is made up of equations turned into code, and the equations MUST be based on assumptions. Ergo, a model can only be the preconceptions of the researchers, "mathemitized", and DESIGNED to give them the results of their preconceptions. It is cartoon city stuff.

Folks, when you see the word "model" in an article about science, ignore it.

ONLY when each and every equation included has been TESTED empirically (in the real world), over and over, is a model correct - like in models for designing buildings and bridges. If it is on the frontiers of science, where not everything is known, then it is a cartoon and not worthy of your attention.
SteveGinGTO
1 / 5 (3) Oct 15, 2015
@24volts: "Since when did something cool faster on the inside than the outside? That doesn't make any sense at all to me."

Exactly. Then if you go over to another current PhysOrg article at http://phys.org/n...tml#nRlv "How a change in slope affects lava flows" (September 15, 2014)", that begins:

"As soon as lava flows from a volcano, exposure to air and wind causes it to start to cool and harden. Rather than hardening evenly, the energy exchange tends to take place primarily at the surface."

BINGO! The cooling starts on the outside, because heat flows from hot to cold.

This article is WRONG about cooling faster on the inside.

Wrong assumptions = wrong conclusions.

PhysOrg seemingly doesn't even READ their articles in order to make some consistent WHOLE out of things or comparing against known principles. They just accept articles without any screening. Just to fill up their site. Otherwise how do they have conflicting science here?
SciTechdude
5 / 5 (3) Oct 16, 2015
Every time one of you posts a "gotcha" point that you pulled out of your ass, a troll gets his wings. http://www.damnin...e-of-it/
docile
Oct 20, 2015
This comment has been removed by a moderator.
docile
Oct 20, 2015
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shavera
5 / 5 (2) Oct 20, 2015
Reading the actual article I cannot find any reference to cooling "from the inside out." It refers to cooling from the top down and (from the best I can read) more-or-less uniform cooling along a horizontal slice.

I'd be interested in understanding where the author of this summary article got the notion of 'inside-out' and where it's represented in the paper.
docile
Oct 20, 2015
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SuperThunder
3 / 5 (4) Oct 20, 2015
I saw the article and clicked on it while talking to myself. I actually said "I didn't know-WHOA!"

I had no idea this happened. This is awesome. It looks like a little piece of V'Ger.
Captain Stumpy
5 / 5 (2) Oct 20, 2015
Every time one of you posts a "gotcha" point that you pulled out of your ass, a troll gets his wings. http://www.damnin...e-of-it/
@SciTechdude
i just drenched my wife in coffee... ROTFLMFAO
thanks!

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