Portraits of Wildflowers

Perspectives on Nature Photography


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From my big Southwest tour I learned the geological term tafoni, a plural noun that refers to “small, rounded, smooth-edged openings in a rock surface, most often found in arid or semi-arid deserts. They can occur in clusters looking much like a sponge and are nearly always on a vertical or inclined face protected from surface runoff.” Such formations have also been called “honeycomb weathering” and “swiss-cheese rock.” The example above is from Arizona’s Wupatki National Monument on October 21st of last year.

The formation shown below from Nevada’s Valley of Fire State Park on October 24th represents a different sort of tafoni that you can imagine inspiring the practitioners of Art Nouveau.

To learn more about tafoni and see many more instances, check out Kuriositas or Wikipedia.


© 2017 Steven Schwartzman


Written by Steve Schwartzman

January 31, 2017 at 5:00 AM

11 Responses

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  1. It is fascinating to see what changes can be wrought on the face of rock. Did you see the article this morning about the crack that opened up in Arizona?


    January 31, 2017 at 7:13 AM

    • I hadn’t seen anything about that in the news but I found an article at


      The statement that “Cook suspects that heavy rains in 2014 and 2016 helped open up the surface to reveal the deep fissure below” reminded me of our drive into Arizona in the fall of 2014. We had intermittent heavy rain all afternoon, and when we arrived at our hotel in Phoenix early in the evening we found the place dark because storms had knocked out the electricity there. Not knowing when the power would get restored, we had to scrounge for another hotel to stay that night.

      Steve Schwartzman

      January 31, 2017 at 7:25 AM

      • You keep getting rained on when you take trips, don’t you? That is a shame.


        February 1, 2017 at 7:52 AM

        • On the whole, we didn’t encounter a lot of rain on the 2014 trip. Rain hit us during the recent trip at Valley of Fire in Nevada and for several days near San Francisco, but even on those days the rain let up enough for us to go outside. On a long trip, it’s inevitable that you’ll get rained on somewhere.

          Steve Schwartzman

          February 1, 2017 at 7:59 AM

  2. What a great phenomenon. I don’t remember seeing tafoni, though I surely must have been in places where they existed. I followed your links, and went a little farther, to this page. Then, I learned that tafoni have been found even on Mars. There’s something to ponder.

    It’s interesting how your photos differ. I read that there’s such a thing as relic tafoni: tafoni that no longer are actively enlarging because lichen or other biological coatings inhibit the differential weathering.There seems to be rock varnish in the second photo. I wonder if it would function in the same way?

    I like how the photos from Arizona and Nevada differ in color and form. The first does look like a loofah. In a quirkier association, the second reminded me of Richard Harris’s song, “MacArthur Park” and its lyrics about the park “melting in the dark / All the sweet, green icing flowing down.” In this case, the icing’s pink, and it was rock that was left out in the rain.


    January 31, 2017 at 7:34 AM

    • Now you have one more reason to visit the great Southwest. It’s a lot more accessible than Mars.

      Relic tafoni strike me as akin to stalactites that stop growing after the dripping water dries up. In looking at the second photograph, I also noticed the desert varnish, which is another geological phenomenon I learned about from this trip. The weathering is so slow that we couldn’t observe the effects directly, but I’ll bet geologists could compare multiple adjacent pairs of tafoni, one member with desert varnish and the other without, to see whether on average the varnish impedes the formation of tafoni.

      Speaking of comparisons, your mention of “MacArthur Park” reminds me that in Austin some years ago we attended a small-venue performance by Jimmy Webb. I had the orchestrated version of that song in my head, but he sang it with just a piano. Both versions work.

      Steve Schwartzman

      January 31, 2017 at 8:01 AM

      • I didn’t make the great Southwest today, but I did head southwest, to Brazoria County. I found some unusual things, including this. It reminded me of your tafoni as soon as I saw it, even though it’s more sand than rock.

        The larger structure this was part of looked like a cross between a huge crawfish chimney and a really big fire ant mound, with tafoni-like cavities all around. It was at least two feet high and easy to spot, because they just burned that section of prairie last Monday.

        I couldn’t figure it out, so I started looking around when I got home. I discovered there are people making sandstone out of sand by using, among other things, Bacillus pasteurii. A Scientific American article says, “A microorganism called Bacillus pasteurii, which is naturally occurring in wetlands, can turn loose media, such as sand or soils, into rock-solid stone in about a day by creating calcium carbonate.”

        And this article on sandstone-making microbes adds support: “The bacterium causes calcite, or calcium carbonate, to precipitate, which glues the grains together. Inject sand with cultures of these bacteria, feed them well, provide oxygen and a source of calcium, and they will turn loose sand into solid rock.”

        Given that prescribed burns result in higher levels of soil bacteria activity, and given that B.pasteurii is common in our soils, I can’t help but wonder — were these cavities eroded, or accreted? Or both? Anyway, I thought you’d be interested. It’s worth a stop by the Field Office the next time I’m down there.


        February 5, 2017 at 7:52 PM

        • Thanks for the information. All the processes your links describe are new to me. I’m often impressed by the things that people have figured out.

          Steve Schwartzman

          February 14, 2017 at 9:58 PM

  3. It was interesting to learn that this effect on rocks has a name, thank you kindly for the information. I have seen a similar effect on limestone rocks on beaches in Southern Spain and always photographed them, it’s such an attractive phenomenon.


    February 4, 2017 at 8:30 AM

    • You’re welcome for the info, which was new to me too. Scientists are fond of naming things, so it’s not surprising that this kind of formation has a name. It’s good to hear that you’re familiar with tafoni from quite a different place than the American Southwest.

      Steve Schwartzman

      February 4, 2017 at 1:16 PM

  4. […] After a couple of hours at Sandstone Bluffs in west-central New Mexico’s El Malpais National Monument, on October 14th we drove the short distance back to New Mexico Highway 117 and continued south toward our ostensible destination. We hadn’t gone far when a fabulous cliff appeared on our left. NM 117 offered few safe spots to pull over, but I found one, determined as I was not to let the cliff pass unphotographed. I’m not sure how tall it is, but compare the trees in the picture’s lower right. When I looked more closely at the natural markings on the cliff, I easily imagined I was seeing some sort of fancy hieroglyphics or Sanskrit or Arabic writing engraved in stone, or perhaps delicate ivory carvings. Imagination aside, the markings might have been tafoni. […]

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