Have you ever wondered what these holes in the sandstone walls are? If you have, you’re in luck! If you haven’t – well, you’re still in luck because you’re about to find out! They’re called Tafoni.
What are Tafoni and Where are they found?
Tafoni are naturally forming circular or ellipsoidal rock cavities. These weathering features include tiny pits, softball-sized cavities, and even truck-sized caves! Tafoni typically develop on inclined or vertical surfaces and are present on the surfaces of many different kinds of rocks. Tafoni are located in many geographical settings around the world but are mainly found in coastal areas or semi-arid and arid deserts – including Antarctica!
How do they form?
Formation of tafoni is completely dependent on the region in which they’re found. Although it’s not known for sure how tafoni form, there are a number of hypothesis that try to answer the common questions surrounding their formation:
- Salt Weathering - salt crystals form in a small cavity and knock off rock particles. Over time, the cavity grows with every particle that is dislodged
- Differential Cementation – chemicals in ground water create a harder surface when they exit the rock. This allows for the rock face to erode at different rates with the hardened areas eroding slower which causes the pits to erode faster and more dramatically.
- Variations in Permeability – As groundwater travels downward through rock layers, it can reach a layer that isn’t as permeable as the others. When this happens the water will travel horizontally along that layer and, when it exits at the face, can cause erosion by the removal of material.
Logging Requirements
Please email me the answers to the following questions:
- Do you see a pattern in the distribution of the tafoni? i.e. – clusters, lines, pairs, etc.
- Based on the observed pattern, and knowing that water can travel through sandstone, what do you think is the most likely explanation for the formation of these tafoni?
- If you’re able, look at the “floor” of one of these tafoni. Describe the soil that you find. Note things like grain size, texture, smell, soil make-up, et cetra.
- What other forms of erosion do you see around the area?
Not required but highly encouraged- take a picture of the tafoni you observed and post it with your log.
*I realize there are plenty of prime examples of tafoni throughout the park so I am allowing these questions to be answered based on other locations. However, all I ask is that when observing tafoni at another location, please send the coordinates along with your answers.
For more information:
- Deserts by Marco Stoppato and Alfredo Bini
- Process Geomorphology - 5th Edition by Dale F. Ritter
- Tafoni.com – a website dedicated wholly to Tafoni.