Saturday, 2 August 2008

Tasman National Park - 2

In addition to the geological features in yesterdays post, the Tasman National Park also has the Tessellated Pavement

Tessellated Pavement


This siltstone rock platform has the appearance of being tessellated or tiled. Geological stresses have caused the jointing (cracks) in the siltstone. A combination or chemical and physical processes have then eroded the surface and creating the tiled appearance. The physical erosion (wave erosion) caused by water and rock fragments washing over the platform has a greater effect on the joints. The chemical erosion (salt wedging) has a greater effect on the surface between the joints. This is caused by salt crystallising between the rock grains. As the salt crystals grow between the rock grains, they cause the rock surface to flake away.

The above processes, if I have described them clearly, will explain the two main features on the rock platform, namely loaves and pans.

The area nearest the sea is under water longer and thus experiences more physical erosion. This eats away at the joints leaving a loaf formation.

Loaves


The area furthest from the sea is left high and dry for longer thus aloowing for greater development of salt crystals and less physical erosion from the sea. This eats away at the sutface of the rock and the joints are left like little ridges, thus forming a pan shape.

Pans


6 comments:

  1. Very interesting rock formations and the description was great.

    ReplyDelete
  2. Hi Mosura, nice photos. The Tesselated Pavement is a very interesting feature. As I recall, it was also the subject of Norm Sanders' PhD dissertation. I had to write about it when doing Geology many years ago. His dissertation was held in the Geography library at the University of Tasmania at that time. The assessment of the way in which the formation of the various parts of the pavement had occurred was extremely interesting, and is well worth a read. I'll have to see if I can find my own report; I remember salt having a strong role.
    I worked on the particular assignment in concert with a friend, and I think we were the only ones who ferreted out Norm's paper. In the end, the teacher decided we'd copied each other's work, and gave us half marks each. It was the most unjust decision I'd had visited upon me at the time.

    ReplyDelete
  3. *The above processes, if I have described them clearly, will explain the two main features on the rock platform, namely loaves and pans.*

    hi Mosura,

    yes, you have explained it clearly, as it now makes sense to me. Thank you.

    Gaye

    ReplyDelete
  4. Thanks Mick, Mark, and Gaye

    Glad it maks sense Mich and Gaye.

    Thanks for the info re Norm Sanders. That paper would be either a great read or a great cure for my insomnia. Kind of a win / win situation :-)

    ReplyDelete
  5. Hi Mosura
    Two memories for me - The Tessellated Pavement (which I saw in about 1980, and Norm Sanders, who I remember from my early days of interested observer of "Green" politics (when Norm was a Democrat Senator - before the "greens" became "Greens").
    < humming to myself>
    "Thanks for the Memories".
    Denis

    ReplyDelete
  6. Thanks Denis .....and what would we be without our memories? (rhetorical question)

    ReplyDelete