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:

[MNJohnnie]

That is a natural formation? How cool!

[mass55th]

Wow! You are a brave soul. I hate heights. I had enough trouble walking up all the steps and inclines just to get this picture:

Our tour guide warned us against going beyond the safety zones, saying he'd be pretty ticked off if any of us fell, and he had to haul our suitcases all the way over to the cliff to throw them over after us.

[CholeraJoe]

Kewl. For everyone else's benefit, here's a closer shot of the castle in mass55th's pic:

[SuziQ]

We’ve been thinking of going to Yosemite someday, maybe we’ll do the Mammoth Lakes are on that trip to CA, as well!

[SuziQ]

Our tour guide warned us against going beyond the safety zones, saying he'd be pretty ticked off if any of us fell, and he had to haul our suitcases all the way over to the cliff to throw them over after us.

*snort*

[SuziQ]

So, did folks use those cool basalt rocks to build castles, etc.?

[CholeraJoe]

I never saw any castles in Ireland made out of basalt. Most of the castles were granite.

[mass55th]

So that’s what it looked like up close!! LOL!!

[SuziQ]

I just wondered since those basalt rocks were so regularly shaped. I wonder if they’d work for masonry?

[bigheadfred]

They work for flower gardens.

[ValerieTexas]

Way cool
I’ve seen similar formations at Mt Rainier in Washington

[cogitator]

Yep. As some pictures noted, Devil's Tower in Wyoming is also columnar basalt. So is Devil's Postpile National Monument. There are also examples in Yellowstone and the Palisades along the Hudson River.

Palisades:

Yellowstone:

[MNJohnnie]

Utterly amazing. They look so regular and symmetrical you would swear they were man made. Thanks for the geology lesson. Great thread.

[wafflehouse]

it contracted in both directions.. however vertical contractions along with gravity just resulted in settling of the lava, where as horizontal contractions caused it to pull apart and crack. thats what i got from wikipedia anyway

[wafflehouse]

here is a good page to check out.. Devils Postpile National Park

[djmv]

ping