Thursday, December 18, 2014

Pictures of the Moment - A What Kind of Pavement?

"A what kind of pavement?" I asked the unresponsive travel guidebook as we continued our drive tour along the eastern coast of Tasmania.

Tessellated pavement pans, Eaglehawk Neck, Tasmania. Farther from the shoreline than the "loafs" (below) evaporating water leaves salt deposits that more readily corrode softer, more weakly-cemented sandstone of the concave pans than the relatively resistant joint filling between them.

In architectural terms, Encyclopaedia Brittanica defines "tessellated" or mosaic pavement (also known as floor mosaic) as interior or exterior floor covering composed of varicolored stone tesserae (Latin: “dice”), cubes, or tiles of other geometry closely fitted together in simple or complex designs with a durable grout or cement. Think of the courtyard mosaics of Ancient Greece and Rome.

The effect in the natural world is not much different, though the results are monotone, and I could find no evidence of nudity depicted. Eaglehawk Neck on the Tasman Peninsula is perhaps the world's best known example of natural tessellated pavement, and the formations there are in the most common geologic form. A flat outcropping of sandstone is subdivided into generally rectangular blocks by systematic, roughly orthogonal (perpendicular) joint systems, regularly-spaced "cracks" formed during the lithification of the sandstone (which caused a volume reduction). Ongoing differential erosion through weathering along the joints causes the relatively flat surface of sandstone to be either raised (loafs) or recessed (pans) relative to the joints.

The loafs quite remind me of the raised walkways in Pompeii. Perhaps the ancient engineers of Rome sailed here on their own, earlier version of the Kon-Tiki. The pans remind me more of linoleum that is past its prime. However, the natural pavements are far older than their classical counterparts, and the craftsmanship is arguably as sublime.

My beautiful scale model stands on top of a "loaf" formation. Closer to (and often under) the water, here the joints erode more quickly due to abrasive sand channelled between them.

Even from a distance, it's easy to see how the "loafs" in the righthand picture are closer to the shoreline.

Eaglehawk Neck is about an hour's drive from downtown Hobart, Tasmania. Take the Tasman Highway (A3) 14 km east to Sorell, and there turn right on the A9 (Cole Street), and continue 51 km towards Port Arthur and the Tasman Peninsula. We visited here in February of 2009.