Thursday, March 26, 2009

Natural wonders

by Martín Bonfil Olivera
Published on Milenio Diario, March 25, 2009

I have just been to one of the 13 wonders of Mexico: the basalt prisms of Santa María Regla, in the state of Hidalgo.

When he came to Mexico in 1803, Alexander von Humboldt visited these impressive 30 meter basalt columns, of perfec hexagonal shape, that border a ravine as if God had arranged them like giants pencils. They're breathtaking.

But for a naturalist such as Humboldt, and for a relentless atheist like this columnist, the divine explanation is not satisfactory: it doesn't really explain anything. Could there be a natural process that allows hundreds of hexagonal prisms to be formed and carefully stacked ?

Basalt prisms, although rare, are not unique. There are 10 or 15 sites in the world with similar structures: the “giant's causeway”, in Ireland; the “Devils postpile”, in California; the “organ pipes”, in Australia… The formation of these structures doesn't seem to be that difficult.

A second hint is the hexagonal shape of the prisms. There is an old saying in northern Mexico, "as the wagon moves, the watermelons arrange themselves", that accurately applies to this case: spheres tend to accommodate spontaneously so that each one is surrounded by twelve more: it is the most compact arrangement. In the case of circles, the most efficient arrangement is hexagonal: the most compact form to arrange cylindrical columns is so that each one is surrounded by other 6. The hexagonal shape of the prisms is the result of this arrangement. They weren’t constructed and then arranged: they formed in their actual position.

And how could melted lava —basalt is solidified magma— form individual vertical prisms? The answer relies in the existence of self- organized structures in nature. "Bénard cells" are example : when heating a liquid from below, the convection movement —hot water goes up and cold goes down— can form hexagonal columns of water that keep circulating as long as there's a temperature difference. Prisms are fossilized convection cells that were solidified when they quickly cooled down.

The mineral world can form marvelous and arranged structures. The same thing occurs, but augmented, in the living world. Darwin, another naturalist, saw it and explained it. Because of this, and more the basalt prisms of Hidalgo are really worth visiting.

(Take a look at my pictures of the basalt prisms here)

(translated by Adrián Robles Benavides)

To receive Science for pleasure weekly
in your email, subscribe here!

No comments:

Post a Comment