What are Columnar Basalts?

When scientists talk about columnar basalts, they're not referring to the work of Frank Lloyd Wright. Rather, these are other-worldly formations that form in unique ways and are only created by lava meeting a specific set of conditions. Yet even though experts have isolated the factors that contribute to columnar basalt formation, we can still appreciate this geological structure on its own merits--without needing to describe it in terms of what causes it. Columnar basalts (also known as stromatalites) are a very distinctive form of basalt. They have very thin, almost cylindrical layers (hence the name "columnar"), making them look similar to basalts found in other locations that can be attributed to volcanoes. But these rocks were not formed by volcanoes. Instead, they're most likely the result of column-forming microbial processes. Columnar basalt is a variation of basalt that has been cooled in a column shape. The stacks of columns, or tube-like features, are called stellated columns and they form when lava cools very quickly, which can occur offshore. Columnar basalt is a variation of basalt that has been cooled in a column shape. The stacks of columns, or tube-like features, are called stellated columns and they form when lava cools very quickly, which can occur offshore.

1.0Waterfalls in Iceland



Source of Columnar Basalts

Columnar basalts are a product of partial melting and cooling of the earth's mantle which results in the formation of dikes and sills. There are various types of columnar basalts with the most common being oceanic plateaus. Oceanic plateaus form when hot material moves upwards generating magma. As this magma flows out towards the surface it takes on the shape of a plateau as it cools.

Hawaii Volcanic eruption.


Formation of Columnar

Columnar basalts form when magma cools slowly on the ocean floor. The cooling of magma occurs at a very slow and constant rate, allowing large-grained crystals to form uniquely. The small mineral crystals that make up columnar basalts grow in alignment with one another and form columns that can range in width between 1/2 inch(1.27cm) and 3 feet(0.9144m). These columns are vertically oriented, which gives these rocks their name.

The cooling causes the rock to contract into a column that is hollow inside, similar to icicles that drop from roofs in winter weather. Types of Columnar Basalts Columnar basalts form depending on the thickness of the flows that form them and the environment they are deposited in. Through studying these three types of basalts and their environments, geologists have determined why they formed and what makes them different from other similar types.





Characteristic of Columnar Basalt

Columnar Basalts formed from lava that was once forced through Earth’s surface over 200 million years ago. This unique type of rock has many different characteristics, one of which is its hexagonal shape. How could a substance form a hexagonal shape? For starters, you need to dissolve the minerals and crystals in this lava, and you need to do so very quickly. There are three main ways this can happen: 1) the lava cools so quickly that crystals cannot form before it solidifies 2) the lava cools so slowly that crystals cannot form (crystals usually form when pieces move towards or away from each other) 3) the Hawaii hotspot pushed the lava up; this allowed it to flow higher than normal before it broke through and cooled into an extensive collection of columnar basalt.

Where Are They Found?

Columnar basalts are found worldwide where subduction occurs along continental margins. The greatest volume is found in regions such as Iceland, Hawaii, Japan, and Italy, especially among oceanic volcanic arcs. Though not exclusively associated with these areas, most come from large shields (large volcanoes) and hotspot volcanism at the borders between the two subduction zones. Section: Geologic Evidence Columnar basalts have a distinctive structure, color, and texture unique to each location they come from. Columnar basalts were formed under incredibly deep pressure and heat. The rock layers were then cooled in a very short amount of time. When you see them, the columns almost seem fake. They are so perfectly shaped and aligned that they look like they were designed by an architect. 

The greatest volume is found in regions such as Iceland, Hawaii, Japan, and Italy, especially among oceanic volcanic arcs. Though not exclusively associated with these areas, most come from large shields (large volcanoes) and hotspot volcanism at the borders between the two subduction zones. 

Conclusion

 Columnar Basalts are some of the most common, and definitely the coolest looking, types of rocks on Earth. While they may look static and unchanging when you first discover them, there is much more to them than meets the eye. Whether you get a chance to observe these fascinating rock formations in person or through photos online, columnar basalts can teach us a lesson about the never-ending processes occurring deep below our feet.

Well, now you know what columnar basalts are and how they form. I hope that you enjoyed the blog. If you did or if there is anything else you would like to see here on the mpetrogeology, please leave a comment below and make your voice heard!

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