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Planetary Geology on Earth: Cliffside Pockets

A cache by firennice Send Message to Owner Message this owner
Hidden : 01/14/2014
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size:   other (other)

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Geocache Description:


Looking to the North or a bit NorthWest you can see a cliff with the pockets of tafoni in it.  They are about 20-30 yards up the hill in a rock face

  1. Describe the tafoni on the cliffs, are they inform in size? Do they appear to be the same shape?  
  2. Looking at the stone that it appears in, do they appear to have more in some stone bands than others?  Why?
  3. How would you guess these were formed?
  4. Are there any nested tafoni? Honycomb tafoni?

Tafoni are the holes that appear in stone.  Usually in sandstone, granites, and sandstone/limestones.  They seem to appear the most in arid climates. They are formed by a few different ways, ans sometimes in a combination of those forces.

Wind - Wind can blow sand and other granules into a hard surface. Those surfaces can start to pit, eventually forming a small depression.  The grit can eventually setting in there, every windstorm can cause it to swirl in the hole and cause the hole to be expanded larger and larger.

Water - Water from flowing streams can cause something like a tafoni.  These are commonly referered to has a pothole, however this is not considered a tafoni.  Water that freezes and cools on the surface of soft rock can cause small pieces to pop off. Slowly eroding the holes larger.  This can be more common in climates where it is moist, and the sun can cause a warm day, but a freezing night.

The sizes can vary dramatically.  Some material looked at under a microscope can show tafoni, and they can be large enough to ride a horse into. The stone iseft is a factor.  Granite has to wear in a different manner than sandstone.

Lateral or sidewall tafoni is the term used to describe those that form on the edges of a cliff, or the sides of an object.  They can form in many locations (top and bottoms af stones.

Once and a while you can get a nested tafoni.  The term is where some holes (tafoni) are forming inside another larger one. As a bonus, you can look and see nests that are in some of these. (not the same as a nested tafoni.

You can also see what is referred to as a honeycomb tafoni. These tend to resemble an irregular bees honycomb. Small pieces between a number of holes that were formed.

Mars

Not only are these found on earth.  It surprised many people when these were found on other planets.  They appear in a few photos from Mars landers.  They stoked the idea that water in the past may have formed them.  Though it is also possible that some were formed when small round spherules were eroted away)

Photo from NASA viking lander launched in 1985

NASA image by pathfinder. 1998

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