Rock formations in columns, such as basalt columns, have such a regular structure due to the uniform cooling process of the lava during volcanic eruption. This slow and steady solidification allows for the formation of well-defined hexagonal columns.
These regular rock formations often form when fluid volcanic lava floods a valley or covers a large area. This lava gradually cools. Initially, a thick flow of hot lava covers the ground, then as it cools, it contracts, like a cake hardening as it loses heat. During this process, the rock solidifies and cracks in a very regular manner, creating fissures similar to a mesh of polygons. Typically, these cracks outline five or six-sided shapes. The distinct columns we observe today are directly the result of this regular cracking mechanism due to the gradual cooling of the lava.
When hot lava flows and begins to cool, it loses heat. This drop in temperature leads to a contraction of the rock material: in other words, the rock slightly shrinks as it cools, and this contraction creates internal stresses everywhere. Quite quickly, these stresses become too significant and crack! They suddenly release by forming fractures, also known as thermal contraction cracks. These fractures generally appear at the surface of the cooled lava and then extend inward, forming regular networks of joints that delineate columns. The structure becomes regular because the fractures distribute themselves in the most efficient way to uniformly relieve the stress, often resulting in regular geometric shapes, the most common being the hexagonal prism. Why the hexagon? Simply because it is the geometric shape that requires the least energy to divide a surface into equal segments. In other words, it is practically the most efficient and economical configuration that nature has found!
The cooling rate directly affects the regularity of the columns: the slower and more uniformly the rock cools, the more regular the cracks will be. The type of lava, its viscosity, and its chemical composition also greatly influence the final structure. Fluid basaltic lava generally cools homogeneously, promoting beautiful regular columns. In contrast, a more viscous rock forms irregular cracks. Regularity can also sometimes depend on the thickness of the lava flow: a thick flow cools slowly and often results in well-structured formations. Other aspects not to be overlooked are the underlying terrain and the presence of water. Water often accelerates cooling in certain areas, which can create local irregularity. Finally, the internal mechanical stresses related to gradual shrinkage play a crucial role in shaping these regular geometric fractures that give the columns their almost sculptural appearance.
Several scientists have observed that when cooling, certain volcanic rocks shrink in a fairly regular manner. Researchers have studied this in the laboratory using simple physical models, such as cornstarch or dried mud that cracks as it dries. They found that these systems spontaneously develop regular geometric cracks, often in hexagons, as this shape best distributes the accumulated stress. Computer simulations confirm that these regular patterns naturally emerge during cooling, without the need for a prior structure. These studies show that today we can easily predict, with just a few precise physical parameters, how these beautiful regular columns will appear in nature.
An emblematic example: the Giant's Causeway in Northern Ireland. These thousands of perfectly interlocking hexagonal columns are so regular that they give the impression of an artificial pavement made by giants (hence the name!). On the United States side, the Devils Tower (Wyoming) impresses with its tall vertical columns, known among other things thanks to the film "Close Encounters of the Third Kind." Another international star: the basalt columns of Iceland, notably at Svartifoss, a waterfall that cascades in front of black and regular basalt columns. Finally, in France, there are beautiful similar formations, such as the famous basalt columns in the Massif Central region or those in the gorges of the Ardèche. All these spectacular formations mark the landscapes and attract both tourists and curious scientists.
The impressive regularity of the basalt columns has inspired several legends throughout the centuries. For example, according to a popular Irish legend, the Giant's Causeway was said to have been built by the giant Finn McCool.
Recent studies using numerical simulations show that cooling rate is a key factor that determines not only the size of the columns but also their regularity and final geometric shape.
Basalt columnar structures are not exclusive to Earth: the Mars Reconnaissance Orbiter has identified similar rock formations on Mars, indicating that rapid lava cooling has also occurred on the Red Planet.
The Giant's Causeway in Northern Ireland has about 40,000 hexagonal rock columns. This spectacular volcanic formation has been a UNESCO World Heritage Site since 1986.
The formation of these columns can vary depending on the size and environmental conditions, but generally, their formation takes several decades to several hundreds of years. Slow cooling is essential to achieve regular structures.
Among the most famous rock formations are the Giant's Causeway in Northern Ireland, Devils Tower in the United States, the Fingal's Cave on the Isle of Staffa in Scotland, and the Basalt Columns of Puy-en-Velay in France.
Sure! Here’s the translation: "Yes, these formations can be found in different environments around the world: from humid and temperate climates to more arid regions, as their formation depends more on volcanic processes and local physical conditions than on the climate itself."
The hexagon is the most stable and energy-efficient geometric shape when it comes to fracturing a uniform material that is contracting. The hexagonal geometry results from mechanically uniform stresses distributed within the cooling lava flow.
Yes, these formations evolve slowly over time due to physical, chemical, and biological erosion processes, which gradually alter their initial appearance. However, these changes are often imperceptible on a human scale.
No, the majority of these formations do indeed result from the cooling and contraction of lava flows, but there are also some similar structures arising from sedimentary processes or due to the differential weathering of sedimentary rocks, although these cases are less regular and widespread.
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