IdeaLiza: Honeycomb weathering and GeoLogs

Over the past five or so months my partner R. and I have slowly been exploring some of Sydney’s beaches. With neither of us being used to living in a big city, we were particularly drawn to the areas that, well, didn’t feel like a big city, and the beaches that weren’t overlooked by huge houses. Of course, some of these beaches have their own charm – just not the charm we were after.

Maroubra is probably our favourite of the beaches we’ve visited so far. The beach itself is fabulous, but it also has great rocks at either end to explore, and a path along the cliffs to the south of the beach with spectacular views through the coastal vegetation.

One of the first things we found to explore at Maroubra was the rocky headland at the north of the beach. These rocks have exquisite weathering patterns peppering their surface. Here are a few of the pictures I took.

My geology knowledge is basically non-existent, but I’m pretty sure these pictures show honeycomb weathering, otherwise known as miniature tafoni weathering, cavernous weathering, fretting, and alveoli weathering. The basic mechanism of honeycomb weathering starts with salt being deposited on the rock, in this case probably by saltwater spray or by the wind. When the salt solution begins to evaporate the salt starts to crystallise in the porous rock, separating the mineral grains and leaving the rock open to other forms of weathering. Over time, and many cycles of wetting and drying of the rock, these amazing honeycomb patterns emerge. Honeycomb weathering isn’t just limited to coastal cliff faces, but can occur on building stones, in hot deserts, and at the poles. There is even some evidence of honeycomb weathering on Mars [1].

I've featured these rock patterns at Maroubra on one refillable notebook so far, and am planning on further books all featuring different pictures of the rocks. R. suggested a great name for these books: GeoLogs.