<p>I don't know if anyone is still interested in this question, but I am doing research on Uluru (a.k.a Ayers Rock), Australia, and the Mitten Ridge Sinkhole in Sedona, AZ (A very interesting combination of locations.).</p>
<p>I have a photo just outside the sinkhole showing the sidewall of the Supai Sandstone. The sandstone is pitted just like honey-comb tafoni. Uluru has the caves everyone is familiar with around much of its base and some armchairs and other gnamma structures from its base to its peak, and a few tafoni that Twidale identifies on its sides. Uluru also has a coat of hematite completely covering it, 2-3 cm thick. Everyone wants to produce hematite from rust or a biogenic source, but the only way I can prove the formation of that much hematite, that thick, is by a great deal of heat, 800-1000 °C. It is done with terracotta clay in ceramics class regularly.</p>
<p>The Mitten Ridge sinkhole was formed by hot gas from the mantle, hot enough to melt garnet, 1950 °C. The ceiling of the sinkhole is covered with tiny garnet crystals that could only have formed in cooling gas. The sinkhole is as far as the gas could melt its way through the strata moving up, maybe 1.5 km height, and it melted its way out into the air, and the tafoni in the sandstone is part of that pathway.</p>
<p>So tafoni are holes melted in the rock when a great heating event happened. I would be glad to post several photos if anyone is interested and can tell me how. Otherwise the papers will go to journals in the next couple of weeks and you can see them there eventually. I will also be glad to correspond with anyone interested on this topic since this only scratches the very surface.</p>

CC BY-SA 4.0
2021-10-24T07:02:49.023Z
Thanks for your interesting contribution. If you would like to include photographs in your answer I find it easier to first load them onto the computer I'm using when posting answer on Stack Exchange. Under your answer selection **Edit** option in gray at the bottom left. Place the computer cursor marker where you want to include a photo. At the header to the Edit section there will be some icons, select the one that looks like a 2D picture of a mountain. When the panel pops up select *Browse* to navigate to where you loaded your photos. Select a photo & follow the instruction in the panel.
Fred
CC BY-SA 4.0
2021-10-24T07:25:29.180Z
Your comment about hematite on Uluru is interesting. It's the first I've come across. All other sources I've come across, until now, explain the red color as [oxidation of iron within the gray arkose sandstone that composes Uluru](https://parksaustralia.gov.au/uluru/discover/nature/geology/).
Fred
CC BY-SA 4.0
2021-10-24T04:34:33.643Z
2021-10-24T07:09:39.413Z
2021-10-24T07:09:39.413Z
WR Barnhart
<p>It is called preferential weathering, but there is another element at play. Before the rock eroded into circular features, there were softer materials present. Those softer materials weathered away first leaving the more resistant host rock (or matrix) behind. The matrix is harder than the softer "clastic" material. When pebbles get washed into the cliff face, the pebbles will slowly break down the softer material first and eventually the wave-action of pebbles will continue to grind as they spin and get rolled around in these little crevasses, which can grow in size as is seen in many Tafoni rock faces.</p>

CC BY-SA 4.0
2019-06-25T14:22:59.933Z
Thanks for the answer! However, I'm not convinced. I've seen this explanation all over the internet and it hand waves over the whole interesting part here, aka the weird pattern. Why, exactly, does the weathering happen in this specific way? And if the explanation is so straightforward, then why is the formation of tafoni so unpredictable? I'm leaning towards the other answer to this question, which cites a number of sources (some quite recent) saying there are many competing hypotheses but no agreement in the field as to their origin.
Owen Versteeg
CC BY-SA 4.0
2019-06-25T08:36:12.407Z
2019-06-25T08:36:12.407Z
Rokman
<p>Expansion of tafoni seems to be based on weathering (seems reasonable enough.) But <strong>what creates them in the first place</strong>? There are a number of explanations online (Wikipedia lists eight plausible causes!) Many websites trying to give a simplified explanation simply say "salt weathering", but from a brief search it's clear that salt weathering is not always the cause of tafoni [0]. They develop on a wide range of rock types, from granite to sandstone to tuffs and conglomerates, and in many situations where they'd be expected to develop they don't.</p>

<p>From what I can tell, they seem somewhat mysterious, and there are explanations that make sense in some cases but not every case of tafoni is well explained. Is there a widely accepted explanation for the formation of tafoni?</p>

<p>Picture of tafoni (Martin Sharman, Wikipedia):</p>

<p><a href="https://i.sstatic.net/FLSVN.jpg" rel="noreferrer"><img src="https://i.sstatic.net/FLSVN.jpg" alt="enter image description here"></a></p>

<p>[0] for example: page 75, Arid and Semi-Arid Geomorphology, Andrew S. Goudie</p>

CC BY-SA 4.0
2019-12-29T08:19:35.700Z
[Here are some pictures](https://www.google.com/search?q=Pirunpes%C3%A4%20Jalasj%C3%A4rvell%C3%A4%20kuvat&tbm=isch) of a supposed tafoni in Finland (a natural 23 m deep hole in bedrock in the municipality of Jalasjärvi). Preferential weathering is the preferred geological explanation. If you wish to see the place, come within seven years from now since the rental of the place elapses after that date.
Heikki Särkkä
CC BY-SA 4.0
2019-12-30T20:21:54.947Z
@HeikkiSärkkä Looks like an interesting place! However, that does not look anything like tafoni to me. Perhaps you're confusing it with another place that does have tafoni, also called the Devil's Nest and located in Finland: https://www.atlasobscura.com/places/pirunpesa-the-devils-nest
Owen Versteeg
<geology><rocks><geomorphology><erosion><weathering>
Is there a widely accepted reason for the formation of tafoni?
Owen Versteeg
# Is there a widely accepted reason for the formation of tafoni?

(Asked by: username_0 on 2019-05-20)

Expansion of tafoni seems to be based on weathering (seems reasonable enough.) But **what creates them in the first place**? There are a number of explanations online (Wikipedia lists eight plausible causes!) Many websites trying to give a simplified explanation simply say "salt weathering", but from a brief search it's clear that salt weathering is not always the cause of tafoni [0]. They develop on a wide range of rock types, from granite to sandstone to tuffs and conglomerates, and in many situations where they'd be expected to develop they don't.

From what I can tell, they seem somewhat mysterious, and there are explanations that make sense in some cases but not every case of tafoni is well explained. Is there a widely accepted explanation for the formation of tafoni?

Picture of tafoni (Martin Sharman, Wikipedia):

[![enter image description here](https://i.sstatic.net/FLSVN.jpg)](https://i.sstatic.net/FLSVN.jpg)

[0] for example: page 75, Arid and Semi-Arid Geomorphology, Andrew S. Goudie

**Tags:** geology, rocks, geomorphology, erosion, weathering

> **Comments:**
> **username_1**: [Here are some pictures](https://www.google.com/search?q=Pirunpes%C3%A4%20Jalasj%C3%A4rvell%C3%A4%20kuvat&tbm=isch) of a supposed tafoni in Finland (a natural 23 m deep hole in bedrock in the municipality of Jalasjärvi). Preferential weathering is the preferred geological explanation. If you wish to see the place, come within seven years from now since the rental of the place elapses after that date.  
> **username_0**: @username_1 Looks like an interesting place! However, that does not look anything like tafoni to me. Perhaps you're confusing it with another place that does have tafoni, also called the Devil's Nest and located in Finland: https://www.atlasobscura.com/places/pirunpesa-the-devils-nest  

---

## 2 answers

### Answer by username_2 on 2021-10-24. Score: 2

I don't know if anyone is still interested in this question, but I am doing research on Uluru (a.k.a Ayers Rock), Australia, and the Mitten Ridge Sinkhole in Sedona, AZ (A very interesting combination of locations.).

I have a photo just outside the sinkhole showing the sidewall of the Supai Sandstone. The sandstone is pitted just like honey-comb tafoni. Uluru has the caves everyone is familiar with around much of its base and some armchairs and other gnamma structures from its base to its peak, and a few tafoni that Twidale identifies on its sides. Uluru also has a coat of hematite completely covering it, 2-3 cm thick. Everyone wants to produce hematite from rust or a biogenic source, but the only way I can prove the formation of that much hematite, that thick, is by a great deal of heat, 800-1000 °C. It is done with terracotta clay in ceramics class regularly.

The Mitten Ridge sinkhole was formed by hot gas from the mantle, hot enough to melt garnet, 1950 °C. The ceiling of the sinkhole is covered with tiny garnet crystals that could only have formed in cooling gas. The sinkhole is as far as the gas could melt its way through the strata moving up, maybe 1.5 km height, and it melted its way out into the air, and the tafoni in the sandstone is part of that pathway.

So tafoni are holes melted in the rock when a great heating event happened. I would be glad to post several photos if anyone is interested and can tell me how. Otherwise the papers will go to journals in the next couple of weeks and you can see them there eventually. I will also be glad to correspond with anyone interested on this topic since this only scratches the very surface.

> **Comments:**
> **username_3**: Thanks for your interesting contribution. If you would like to include photographs in your answer I find it easier to first load them onto the computer I'm using when posting answer on Stack Exchange. Under your answer selection **Edit** option in gray at the bottom left. Place the computer cursor marker where you want to include a photo. At the header to the Edit section there will be some icons, select the one that looks like a 2D picture of a mountain. When the panel pops up select *Browse* to navigate to where you loaded your photos. Select a photo & follow the instruction in the panel.  
> **username_3**: Your comment about hematite on Uluru is interesting. It's the first I've come across. All other sources I've come across, until now, explain the red color as [oxidation of iron within the gray arkose sandstone that composes Uluru](https://parksaustralia.gov.au/uluru/discover/nature/geology/).  

---

### Answer by username_4 on 2019-06-25. Score: 0

It is called preferential weathering, but there is another element at play. Before the rock eroded into circular features, there were softer materials present. Those softer materials weathered away first leaving the more resistant host rock (or matrix) behind. The matrix is harder than the softer "clastic" material. When pebbles get washed into the cliff face, the pebbles will slowly break down the softer material first and eventually the wave-action of pebbles will continue to grind as they spin and get rolled around in these little crevasses, which can grow in size as is seen in many Tafoni rock faces.

> **Comments:**
> **username_0**: Thanks for the answer! However, I'm not convinced. I've seen this explanation all over the internet and it hand waves over the whole interesting part here, aka the weird pattern. Why, exactly, does the weathering happen in this specific way? And if the explanation is so straightforward, then why is the formation of tafoni so unpredictable? I'm leaning towards the other answer to this question, which cites a number of sources (some quite recent) saying there are many competing hypotheses but no agreement in the field as to their origin.  

---

