The basalt columns have such perfect regularity because they form during the uniform and rapid cooling of basaltic lava, which results in a regular contraction of the rock and creates these characteristic hexagonal structures.
When a very hot basalt lava flow begins to cool, its volume gradually decreases: this is the famous thermal contraction. The rock slowly loses its heat, causing the material to shrink. And since the cooling is relatively uniform, the contraction leads to regular fissures, spaced at fairly regular intervals. As a result, these cracks form structures in very sharp geometric prisms, often hexagonal, because this is the ideal shape to evenly distribute the stresses generated by this thermal shrinkage. This beautiful geometry can be observed at different scales, from small rock pavements to the impressive basalt columns that sometimes form entire cliffs.
When the hot lava begins to cool, it contracts as it gradually loses heat. However, this contraction does not occur without tensions: mechanical stresses arise in the solidifying rock as it loses volume. The rock becomes trapped, constrained by the already cooled material around it, and cannot shrink freely. As a result, an accumulation of internal stresses eventually creates well-defined cracks. Just like when mud dries in the sun into fairly regular pieces, basalt also seeks to divide into organized structures under the influence of accumulated tensions. These cracks often take on a hexagonal shape because it is an energetically efficient way to relieve these internal stresses, giving rise to the famous basalt columns.
The astonishing regularity of basalt columns is largely due to the crystalline properties of basalt. When this rock cools, its minerals such as pyroxenes, plagioclases, and olivine crystallize according to specific, ordered, and repetitive patterns, creating a regular internal structure. This crystalline symmetry guides the uniform propagation of cracks during thermal contraction, thereby facilitating clean and regular fractures. The more homogeneous the crystallization, the more the columns will take on their famously hyper-regular hexagonal shape. Conversely, if impurities or mineral heterogeneities are introduced, the regularity quickly fades, making the columns more irregular, or even outright flawed. In short, the quality and purity of the crystal make all the difference between a nicely drawn hexagonal column and a random rock mass.
Cracks generally arise from small microscopic defects in the cooling basalt. When the rock contracts as it loses heat, mechanical stresses appear. These stresses accumulate gradually until a crack forms. Once one appears, it progresses quickly and often propagates in a specific direction: the one that best releases all that accumulated energy. This phenomenon of rapid advancement, called crack propagation, occurs in bursts. The crack grows suddenly, stops for a bit, then resumes, generating regular segments that form the famous hexagonal columns. As it progresses, these cracks create regular networks because this is the simplest way to evenly distribute the mechanical stress. This particular dynamic explains why basalt columns have an almost astonishing visual regularity.
The Giant's Causeway in Northern Ireland is undoubtedly the most famous example: nearly 40,000 hexagonal columns, formed during the rapid cooling of a lava flow, create a unique and impressive landscape. Another star formation, the basalt columns of Devils Postpile in California display extremely regular columns, many of which clearly show their hexagonal symmetry. In Iceland, Svartifoss ("black waterfall") cascades majestically surrounded by perfect basalt columns, which even inspire the local architecture, including the iconic church in Reykjavik. Still in Iceland, the basalt cliffs of Reynisfjara near Vik form a stunning wall right at the edge of a black sand beach, a spectacular setting that attracts many curious visitors and photographers. Less known but equally impressive, the basalt columns at the French site Orgues d'Ille-sur-Têt show how the phenomenon can take different but always surprising forms.
Some basalt columns have been used by humans to construct buildings or walls. For example, the Scottish island of Staffa inspired the natural architecture of Fingal's Cave, which is entirely lined with these amazing geometric formations.
The astonishing regularity of the basalt columns has even led to the development of mathematical and physical models that are now used to study other similar natural phenomena, such as the cracking of rocks or dried mud.
Mars also has basaltic formations similar to those found on Earth, which can help scientists better understand the geological conditions of the red planet's past.
Although basalt columns are often hexagonal, they can also take on pentagonal, heptagonal, or even octagonal shapes depending on the local conditions during the cooling of the basalt.
The formation of basalt columns can take anywhere from several decades to several hundred years, depending on the thickness of the lava flow and the local temperature and cooling conditions that determine the rate of thermal contraction.
Sure! Here’s the translation: "Yes! NASA has identified formations similar to basalt columns on the surface of Mars, indicating that volcanic processes analogous to those on Earth have also occurred on the red planet."
Yes, they can still appear whenever a flow of hot basaltic lava cools slowly. For example, relatively recent basalt columns were formed during volcanic eruptions in Iceland.
Although basalt columns often exhibit remarkably regular hexagonal shapes due to the uniform distribution of stresses during cooling, some columns may have 5 or 7 sides depending on the specific cooling conditions.
Among the emblematic examples are the Giant's Causeway in Northern Ireland, the basalt columns of Garni in Armenia, Fingal's Cave in Scotland, and the spectacular formations of Svartifoss waterfall in Iceland.
Basalt is a dark volcanic rock resulting from the rapid cooling of lava rich in iron and magnesium. It is common on Earth but also observed on other planets, such as Mars.
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