As the plaque tells us, ‘its story began in an ancient, cold sea’. Today, the tessellated pavement lives on a mysterious shoreline at the bottom of the world.
Some weed, double-crosses and an island
I stood on the edge of Pirates Bay – a dark sea that lapped the shore like black sludge, dragging seaweed across pockets of vegetation. I looked down at slabs of criss-crossed stone that faded into the shallows. Beyond this, a small island sat beneath billowing clouds of purple and grey.
I was on Tasmania’s Eaglehawk Neck – a narrow isthmus where men once risked their lives trying to escape. I was here to see the tessellated pavement, a geological phenomenon where striking rock patterns were fashioned by silt, salt, sand, water and time.
Formation of the tessellated pavement
A long, long, long time ago (roughly 290 million years), silt was transported to a depression in then central eastern Tasmania via streams from higher ground. This silt eventually turned into siltstone, which formed cracks due to stresses in the Earth’s crust. The silt was deposited from three different directions: north-north-east, east-north-east and north-north-west. Hence the criss-cross pattern we see today.
The tessellated pavement was formed by what’s known as ‘loaf’ and ‘pan’ erosion.
When the pavement close to the shore dries out at low tide, salt crystals form, which erode the flat surface of the rock more quickly than its joints. This creates the accentuated ridges you see at the tessellated pavement known as ‘pans’.
The section of the tessellated pavement that’s beyond the shore – which spends more time underwater – has formed ‘loaves’. Here salt crystallisation is less significant, so the prominent form of erosion is sand transported by water. Water creeps into the joints of the stone, eroding the edges more quickly and creating the ‘loaves’ we see today.
Eventually these loaves get dislodged by waves. However before this happens, fresh erosion is already occurring in the cracks and the cycle starts anew. As you can see, the loaves look a bit like bread concocted in an elemental bakery (in a sense they were).
Although I haven’t done it yet, you can walk to Clydes Island – which lies just offshore – at low tide. Allegedly there are grave sites here along with exceptionally fine vistas stretching roughly 20 kilometres south to Cape Hauy.
It’s a plan for my next visit.
Have you been to the tessellated pavement? What was your experience like?