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cakewalk
Joined: 03 Jan 2003 Posts: 512
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Posted: 9/6/2006, 10:02 pm Post subject: Cakewalk's book of secret places..... |
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Im all about solitude and exploring areas off trail. ( I know...I Know! )
In the gallery, please find my first ever " Expose " of a cool secret place.
Please help me understand whats going on here.... Petrified sand dunes? It's such a strange contrast to the surrounding area, which is lava rock so common to this area.
The last picture is an example of the abundant quartz chalcedony that is strewn about everywhere, but limited to this small " sand dune " looking area.
Pics are
Here |
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Sparrish
Joined: 04 Jul 2004 Posts: 239 Location: Phleeenix
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Posted: 9/7/2006, 6:08 am Post subject: |
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The whiter rock is most likely volcanic tuff (consolidated pyroclastic). Does the white rock have small hunks of different shaded and sized material in it or is it a consistent grain size and texture? Consistent grain size and texture--along with cross-bedding--implies sorting by wind action. Small hunks of different shaded material in a light matrix imply an explosive volcanic eruption.
I doubt the formation is dune related as there dose not appear to be any cross-bedding. In addition, there appear to be darker volcanics strewn about on top and near the formation, which is another clue to volcanism _________________ “And all her face was honey to my mouth,
And all her body pasture to mine eyes;”
--A. C. Swinburne |
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Nighthiker
Joined: 05 Jan 2003 Posts: 1714
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Posted: 9/7/2006, 8:51 am Post subject: |
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Looks like welded tuff, fuzed ash from volcanic activity. Very neat place. |
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cakewalk
Joined: 03 Jan 2003 Posts: 512
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Posted: 9/7/2006, 4:04 pm Post subject: |
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Ash...... That makes sense.
Pretty cool, thanx for the info.
Would that explain the odd quartz formations as well? Was it was spewed from a volano in a near liquid (Taffy like ) form then hardened to its current shape? |
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Sparrish
Joined: 04 Jul 2004 Posts: 239 Location: Phleeenix
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Posted: 9/7/2006, 4:25 pm Post subject: |
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cakewalk wrote: |
Ash...... That makes sense.
Pretty cool, thanx for the info.
Would that explain the odd quartz formations as well? Was it was spewed from a volano in a near liquid (Taffy like ) form then hardened to its current shape? |
The quartz and other minerals such as calcite are products of secondary mineralization. After the tuff is welded in place (it emerges at around 1500 degrees) and cools, it is subject to groundwater intrusion as well as rainfall. All rain is acidic. It reacts with CO2 in the atmosphere as it descends and forms carbonic acid in the process. The rainwater--now slightly acidic--percolates down through the tuff and dissolves silicates in the tuff and in the dark colored basalt. The water, laden with dissolved silicates and calcite travels downward until it reaches a hollow spot in the tuff. As it runs through the hollow spot, a small portion of the water evaporates, leaving behind whatever it picked up on the way. The odd shapes are molds of the hollow spots in the tuff.
It is the same process that creates stalactites and stalagmites in caves. _________________ “And all her face was honey to my mouth,
And all her body pasture to mine eyes;”
--A. C. Swinburne |
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cakewalk
Joined: 03 Jan 2003 Posts: 512
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Posted: 9/7/2006, 6:12 pm Post subject: |
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Sparrish, did you stay at a Holiday-Inn Express last night?
Seriously, I appreciate your insight. Thanx for answering my questions. |
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Sparrish
Joined: 04 Jul 2004 Posts: 239 Location: Phleeenix
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Posted: 9/7/2006, 7:25 pm Post subject: |
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No, but while in school, I fell in love with geology and took every course that was offered. I still have rocks in my head and I love to discuss the science.
If you want a nice intro to geology, read John McPhee's "Annals of the Former World" ( a large hard-bound volume of 5 books) or start with the first single volume: "Basin and Range", which is available in paperback. _________________ “And all her face was honey to my mouth,
And all her body pasture to mine eyes;”
--A. C. Swinburne |
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