What is the Tessellated Pavement
Intro: Sometimes it is hard to believe certain rock formations are natural… and this is definitely the case with a place in Tasmania called the Tessellated Pavement. It is named this due to the tessellated (i.e. tiled-like) appearance of the rocks along the water. This little tourist spot is near Eaglehawk Neck, on the way to the famous Tasman Peninsula, and only about an hour drive from Hobart. Not only is the Tessellated Pavement a spectacular sight (and photographer’s dream), but it also is a unique geological phenomenon…
Science Spiel: Cracks and salt (Geology, Geomorphology)
The rock that comprises the Tessellated Pavement is mostly siltstone that formed in the Permian (about 300 million years ago), by sediments that accumulated on a relatively low-lying area. The sediments eventually got compacted and lithified to form the solid siltstone. Local stresses at the Earth’s surface then caused the siltstone to crack and fracture in certain directions, this is called jointing. There are three mains sets of joints; ENE, NNW, and NNE. The fact that they are mutually cross-cutting without off-set each other is a key observation that tells you the joints formed at the same time.The way they criss-cross each other is what creates the tiled-like appearance.
But wait, the story doesn’t end there… time and water also played (and continue to play) a role in creating this site.
The rocks are currently on an intertidal seaward platform, and thus years and years of erosion (i.e. since sea levels stabilised in the area ~6000 year ago), has exaggerated the tessellation appearance (Leaman, 2001). The constant action of the salt water splashing over and partly covering the rocks with changing tides has lead to the accumulation and percolation salt water on the rocks, particularly within the joint. As the water gets evaporated by the sun, salt crystals forms and as they grow they exert pressure on the rocks causing rocks and joints to flake away and be more susceptible to erosion.
The salt crystallization mostly occurs in the joints, however, water that pools on the top of the rocks furthest away from the ocean dries the fastest and salt crystallization is more intense on the rock surface there, causing the depressed, or “pan-like” tiles.
The opposite occurs for rocks closer to the water, and therefore only the joint really are visibly depressed, creating the “loaf-like” tiles (Banks et al., 1986; Leeman, 2001).
Final Thoughts: The Tessellated Pavement is a stunning sight that sparks curiosity of visitors. The reason I checked it out is that actually a friend of mine asked me what it was, as it looked man-made to her! Jointing in rocks is not an uncommon thing, but the special circumstances with salt crystal formations and increased erosion really enhanced this pattern. I would highly recommend stopping by this neat place on the way to the Tasman Peninsula, I hope it sparks your curiosity about rocks as well!
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