Local knowledge and scientific process solve mystery of Aran Island boulders

This is a fascinating story about anecdotes, evidence, old techniques and new finds. Take a look.

Old Maps and Dead Clams Help Solve Coastal Boulder Mystery

The three tiny Aran Islands are just off the western coast of Ireland. The elongated rock ridges form a collar along extended stretches of the islands’ Atlantic coasts. The sizes of the boulders in the formations range “from merely impressive to mind-bogglingly stupendous,” writes Dr. Rónadh Cox, who led the research with her Williams College students. One block the team studied weighs an estimated 78 tons, yet was still cut free from its position 36 feet above sea level and shoved further inland.

Armed with equations that model the forces generated by waves, some researchers have concluded that no ordinary ocean waves could muster the force necessary to move the largest of the boulders this high above the ocean surface and so far inland. The math suggests the rocks in the ridges could only have been put there by a tsunami.

The equations tell one story. The islands’ residents tell another. According to some locals, enormous rocks have moved in their lifetimes, despite the fact that there hasn’t been a tsunami to hit the islands since 1755.

“Unless you have little green men from mars doing this on the quiet, it must be storm waves,” Cox said.

Credit: Geology.com

Photo: University of Chicago

The residents had their old anecdotes. The anecdotes are poor evidence on their own but they can LEAD you to gathering better evidence. And, in this case, it worked. The researchers used old maps meticulously produced by hand long ago. The maps were accurate to less than a meter. But then, other lines of evidence corroborated the accounts of recent movement of boulders such as radiocarbon dating and photographic records. All lead them to conclude that no tsunami was necessary. An occasional huge storm wave would do it.

What a lovely example of local knowledge and science working in concert to get to an answer.

  6 comments for “Local knowledge and scientific process solve mystery of Aran Island boulders

  1. Massachusetts
    May 2, 2012 at 5:43 PM

    This reminds me a bit about the boulders in Death Valley that are noted to move, leaving trails on the ground to mark their passing. Ocean waves make sense. I wonder what’s up with the Death Valley boulders? There are indeed some interesting mysteries out there. We shouldn’t abandon science as we investigate, as clearly this story strongly indicates.

  2. Massachusetts
    May 2, 2012 at 5:45 PM

    The little green men comment was interesting in the original story. I’m sure there are extraterrestrial proponents out there advocating non human sentient entities who are involved with these boulders. But storms surges and ocean waves make more sense, don’t they?

    The little people may be strong, but not that strong I’m guessing. 🙂

  3. May 2, 2012 at 5:56 PM

    Here is the definitive bit on the Racetrack Playa in Death Valley. http://skeptoid.com/episodes/4021

  4. May 2, 2012 at 5:56 PM

    Big rocks are mysterious 😛

  5. Massachusetts
    May 3, 2012 at 9:53 PM


  6. Massachusetts
    May 3, 2012 at 9:58 PM

    That’s really amazing. I wouldn’t have thought of that but it’s so simple. I hope they can fully capture the phenomenon soon. Though elves would have been cool too. 🙂

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