Monday, June 16, 2014

How weird landscapes form

A "face" and other alleged structures on Mars are topics that pop up on these pages from time to time.

Prevailing thought is...and with good reason...that these formations are due to to a process called "differential erosion."  I recently found a nifty article that sheds a bit of light on how this works.

The integrity of rocks is variable depending on chemical composition and the conditions under which the rock in question was formed.  Different parts of the same rock can have different levels of hardness and durability.  As the article says:

"Minerals that form under surface conditions of temperature, pressure, and moisture are most resistant to weathering at the surface, while minerals that form deep within the Earth are weakest at the surface. Rocks that are crystalline solids are more resistant to weathering, while those with cracks, joints, and fractures have more exposed surface area prone to weathering. When rocks with different weathering properties are adjacent to each other, the result can be beautiful."

Indeed the surface of Mars is an example given at the page of differential erosion.  Sandstone with variable resistance to erosion shows itself in a stair-step pattern.  Weaker sandstone flattens while the stronger remains relatively intact, giving the appearance of a steep stair.  It's therefore easy to see why someone may mistake such formations as artificial.  As an aside, it's rather marvelous to me how the pic from Mars looks like it might just as easily come from someplace like Egypt or the Southwest U.S. rather than another planet.

Speaking of places closer to home, the link has several other examples of these kinds of weird formations right here on Earth.  One of these is Goblin Valley, Utah.  Once again we're dealing with sandstone layers of variable strength.  As the weaker parts are stripped away by wind, a free-standing, bowling pin-like blob is left.  Check out the pic.  While it might not look like an army of goblins to fantasy gamers, it at the very least resembles a mob of sandy-colored penguins.

Which sounds like a helluva lot of fun now that I say it.

Let us not forget the force of water when it comes to erosion.  The Sea Stacks of Italy are a great example of water at work.  Note the cavern and bridge shapes resulting from weaker strata at sections of the base.

But what of the notorious "face?" Turns out there are plenty of erosion-formed faces around here as well.  The Weather Channel has an entire list of them.  I am especially enamored of the "Sphinx of Romania." It's got a Castle Grayskull quality to it.  It's really a game of staring up at puffy clouds and discerning non-existent "faces" or if not nonexistent then organic and unintentional.

Hey!  What's that one look like to you?

Shatner.  It looks like William Shatner.

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