Geology Picture of the Week, April 27-May 3, 2008: Giant's Causeway, Ireland

simonward.com ^ | Simon Ward

[cogitator]

Just felt like some columnar basalt this week. The second one is from here: 2ireland.org

[cogitator]

** ping! **

[Andyman]

Hey! I've actually been there. It's fantastic.

[doodad]

Here is some homegrown. Really interesting spot. Sheepeater's cliff.

[VaRepublican]

Ok I’ll bite, how does that happen naturally. I know I could look it up but if your gonna post then I’m going to ask.

[VaRepublican]

http://2ireland.org/photos/Ireland/northcoast/causeway3.jpg
that pic almost looks fake, so truth is still stranger than fiction?

[Andyman]

As the lava cooled rapidly, contraction occurred. While contraction in the vertical direction reduced the flow thickness (without fracturing), horizontal contraction could only be accommodated by cracking throughout the flow. The extensive fracture network produced the distinctive columns seen today. While most are six-sided, some are anywhere from 5- to 8-sided.

The basalts were originally part of a great volcanic plateau called the Thulean Plateau which formed during the Paleogene period.

Thanks to Wikipedia.

[SuziQ]

Now that’s just COOL! If I ever get to Ireland, I’d like to see those in person!

[SunkenCiv]

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[SunkenCiv]

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[Swordmaker]

Now that’s just COOL! If I ever get to Ireland, I’d like to see those in person!

You can see it in the U.S. at Devil's Postpile National Monument... in California

[Fred Nerks]

Nan Madol, the mysterious structures on a number of islands in Micronesia, used prismatic basalt as the primary construction material:

The 260-foot long north wall of Nandauwas sweeps gracefully upward at its ends. Naturally formed prismatic basalt was laid in skillfully fitted stacks to form the wall.

[Fred Nerks]

This looks like fun? Climbing the basalt columns at Devils Tower:

[CholeraJoe]

I'll see your Giant's Causeway, and raise you a Cliffs of Moher:

And a picture of me in Ireland with the Atlantic in the background:

[Grammy]

Really cool. Thanks

[mass55th]

I was there too in 2006. The view is beautiful!!

[Jessarah]

While contraction in the vertical direction reduced the flow thickness (without fracturing), horizontal contraction could only be accommodated by cracking throughout the flow.

So why did it contract in a vertical direction instead of a horizontal contraction?

[mass55th]

It was fairly misty the day I was at the Cliffs of Moher. You weren’t one of those crazy people who walked out to the edge were you?

[CholeraJoe]

Um, yeah. I was pretty much leaning over the edge when I took this one:

[Andyman]

Sometimes the formation happens vertically, sometime more horizontally. In the hill above the more famous formation most commonly pictured at Giant;s Causeway, there is this formation jutting out of the hill:

These ones are called Organ Pipes. Why they are not geometrically shaped at the top, I don't know.

This shot shows the horizontal and vertical fracturing: