Devils and Giants: Hexagons Explained
Do you remember The Devils Tower from the movie Close Encounters of the Third Kind? Have you wondered what it is and how it came to look the way it does?
Devils Tower, located in Wyoming, is a stock — a small intrusive body formed by magma which cooled underground and was later exposed by erosion. The magma which formed Devils Tower cooled and crystallized into a rock type known as phonolite porphyry. As the rock cooled, it contracted, forming primarily hexagonal (and sometime four, five and seven-sided) columns separated by vertical cracks.
Do you know about The Giant’s Causeway? Perhaps you’ve seen it among the vista shots from Game of Thrones. It is located in County Antrim on the northeast coast of Northern Ireland. An area of about 40,000 interlocking basalt columns, The Giant’s Causeway is the result of an ancient volcanic eruption. Most of the columns are hexagonal, although there are also some with four, five, seven or eight sides.
Why the hexagonal pattern among these igneous protrusions? This is a question which has been on the minds of geologists for hundreds of years. A new study suggests scientists may have cracked the mystery. Literally.
From the abstract of the study titled Why Hexagonal Basalt Columns? published in the Physical Reviews Letters:
“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 “
Computer models used routinely in analyzing stresses in bridges and aircraft parts helped researchers come to their conclusions. As material at the surface cools it shrinks more quickly than the underlying lava, which is still quite warm. The shrinkage causes small cracks to intersect at 90 degree angles, but as the material continues to cool and shrink even further, small cracks consolidate into large ones and the angles between them gradually shift toward 120 degree angles – which is the angle at which the most energy is released.
These hexagonal formations have a place in the history of the battle of geology versus creationism. As Donald Prothero explains when it comes to the history of The Giant’s Causeway:
“Its discovery and description are important pieces in the early history of geology, as many different people in the 1700’s puzzled over it and tried to explain it in the context of Noah’s flood, or gave even more fantastic explanations … Thanks to interference and pressure from an evangelical organization, the Caleb Foundation, there is an exhibit which gives the Young-Earth Creationist viewpoint that the feature is less than 6000 years old, rather than its true date of 60 million years.”
No amount of evidence will ever convince a Young-Earth Creationist that the Earth is older than 6000 years, especially any evidence concerning how science can explain the hexagonal shapes of the rocks. But this discovery is yet another victory for the scientific process. It adds to the ever-growing body of evidence on how things in nature which appear too orderly to have been formed by natural processes turns out to be, in the end, entirely natural.