There is something mesmerizing about patterns in nature.
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| Wasp nest chambers |
When living things create the patterns, we can nod at evolution: the pattern must aid in the survival of the organism somehow, by creating useful structures or conserving resources. Even if no mind is involved, there are genes controlling behavior and orchestrating the pattern.
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| Honeycomb coral slime mold |
When patterns occur in something non-living, though, it feels more mysterious. How can blind chemical or mechanical processes result in intricacy and beauty? A few weeks ago we had the chance to explore Larrabee State Park near Bellingham. There are beautiful eroded rocks along the coastline, sandstone worn by the waves. The sandstone is called the Chuckanut formation, and it is well known to local rock nerds for containing Eocene plant fossils, 34 to 54 million years old. In some places, huge palm fronds have been preserved. The sediments were originally deposited on a tropical coastal plain and were later uplifted and folded into hills. I haven't had a chance to see the palm frond fossils, but we did see another wonderful feature of this rock: lovely patterns of tafoni.
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| Chuckanut formation sandstone |
There seems to be a longer list of what we DON'T know about tafoni than what we do. Tafoni is the name for the pits that have been eroded into a honeycomb pattern. This most often happens in sandstone, but can occur in other rock types as well.
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| Tafoni at Larrabee State Park |
The word tafoni derives from either Greek or Sicilian. In Greek, it means "tomb" and Sicilian it means "holes or windows (taffoni)" or "to perforate (tafonare)," so I'm leaning toward Sicilian as the origin.
Not only is the name mysterious, the process of formation is also uncertain. A likely mechanism involves seawater splashing on the rock. As the seawater seeps in, it deposits salts. The salt crystals grow as the water evaporates, and loosen mineral grains in the rock, which wash away. This explains the holes, but what about the walls? One idea is that algae growing under the surface of the rock helps the walls maintain their structure. But why on earth would this result in such a pattern? Why wouldn't the algae protect the entire surface equally?
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| Tafoni at Larrabee State Park |
In some spots, shallow pits were visible where the tafoni pattern was just beginning to form. I know along rivers rocks can get caught in depressions and wear away pothole formations. I wonder if swirling rocks or even sand grains can help deepen the holes in tafoni?
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Tafoni forming
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Here's one other example of a beautiful, regular tafoni pattern from Salt Spring Island in British Columbia.
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| Tafoni on Salt Spring Island |
Our brains are wired to delight in patterns, and also to seek explanations. Maybe sometimes we need to allow ourselves to be amazed by beauty and mystery; there are so many things about the world still to be fully understood. That said, I hope a geology PhD candidate somewhere figures this one out for us someday.
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