Friday, September 9, 2011

WOGE #307

I finally found it! After searching on and off for almost a month I located the snowy mountains in Christoph Grützner's WOGE #306 in sunny Greece, of all places.  Hopefully my selection for the next edition will be less challenging.  I tried to find a perfect spot for all of the geologists out there who like to take their work home with them.  As always, the first one to find the coordinates and tell us something about the geology of the area will win the privilege of hosting the next WOGE challenge.  (For a more complete explanation of the game go here.) The Schott Rule is not in effect this time.  Enjoy the search.

Now that this edition has been solved, I will add a few pictures showing why I found this area interesting. All photos are by GeoKap
Caves near Gelsunda
"Cave City" upriver at Vardzia
Another view of Vardzia with the Mtkvari River


  1. 41.4628°N, 43.2961°E Perlite Deposit of Toloshi in South Georgia.
    The deposit is situated in Georgia with an extend of 3-4km² and a visible thickness of 5-6m. The deposit is connected with the late Miocene/early Pliocene phase of the Neogene-Anthropogenic volcanism. The perlites are black with a well marked perlite structure, breccia texture and are decomposed into spherical grains. The glassy groundmass makes up 85-90% of the volume, the rock forming minerals 5-6%.
    The Rock-forming minerals are mainly represented by plagioclases of the oligoclase-andesine line, hornblende and more rarely by biotite (source).

    Perlite is an amorphous volcanic glass that has a relatively high water content. When it reaches temperatures of 850–900 °C, perlite softens (because it is a glass). Water trapped in the structure of the material vapourises and escapes, and this causes the expansion of the material to 7–16 times its original volume. Perlite is an excellent filter and is also used for light weight building material and many other purposes (Wikipedia).

    I hope this is the geology you are looking for. At least I did not find any other things about the area.

  2. Congratulations to Felix Bossert, and thank you for sharing the interesting information you found about the perlite deposits and their possible uses.

    When I mentioned that this would be "a perfect spot for all of the geologists out there who like to take their work home with them". I was actually thinking of a much older and simpler way of using the the soft volcanic deposits in this area. As shown in the pictures above, cave homes were dug out of the rock centuries ago near the village of Gelsunda. Further up the gorge that the Mtkvari river (also called the Kura) has cut through the plateau, there is a much more impressive "cave city" at Vardzia. This was a fortress consisting of thousands of rooms on thirteen levels that was built in the twelfth century as protection against the Mongols. It was heavily damaged by an earthquake less than a hundred years later.

    It is interesting that people are still building homes using similar materials, although in a very different way. I look forward to seeing what Felix has in store for the next WOGE.

  3. WOGE #308 has been posted at

  4. uups, did I forgot to post the link to the next Woge? Thank you Matthew for your link.....