What's the Honeycomb Pattern in Some Coastal Rocks?
Have you ever stopped to stare at these mesmerizing patterns on rocks at the beach? Ever wondered how they get created?
They come by many names, but the most common I've seen are tafoni (singular: tafone). They occur pretty much everywhere on the planet, although are most common in coastal areas due to a process called honeycomb weathering.
Honeycombing weathering happens when salt (from seawater or carried with the sea breeze) and water are present on a permeable rock such as granite, sandstone, and limestone. As the water evaporates, the salt crystallizes itself into the pores of the rock. As the environment cycles between wet and dry conditions, the salt crystals continue to pull apart grains from the rock during the evaporation periods.
So why is the rock surface not evenly damaged and eroded? As the salt crystals start to tear grains apart, it starts to form a small dent. The bigger the dent, the more salt and water get trapped inside, thus exasperating the problem. When the holes are too large to allow effective evaporation, the process stops and the holes won't grow anymore.
As far as scientists can tell, salt weathering is the general cause of honeycomb weathering, but it can only be caused by different things in different environments (such as Mars).
References and further reading:
Carlos Rodriguez-Navarro. Origins of honeycomb weathering: The role of salts and wind.
Carlos Rodriguez-Navarro. Evidence of Honeycomb Weathering on Mars.
Nick Doe. What makes holes in sandstone.