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Earth Science Reviews

Storm waves in the west moved boulders onto the top of this cliff

Previously it was assumed that only a tsunami could be that powerful.

NEW RESEARCH SHOWS that storm waves in 2013 and 2014 along the west coast of Ireland were strong enough to move boulders – and deposit new ones on the top of a cliff.

In a new paper in Earth Science Reviews, researchers from Williams College in the US show that the storms shifted smaller boulders as high as 26 metres above high water and 222 metres inland.

Many of the boulders moved were heavier than 100 tons, and the largest moved was 620 tons – the equivalent of six blue whales or four single-storey houses.

They say that it was previously assumed that only tsunamis could move boulders of the size seen displaced in Ireland. But their work provides direct evidence that storm waves can do this kind of work.

The researchers say the work is important as according to the UN, about 40% of the world’s population live in coastal areas (within 100 metres of the sea), so millions of people are at risk from storms.

Understanding how those waves behave, and how powerful they can be, is key for preparation. It is therefore important to know the upper limits of storm wave energy, even in areas where these kinds of extreme wave energies are not expected.

“The effect of the storms of winter 2013-14 was dramatic,” said Dr Rónadh Cox, Professor and Chair of Geosciences at Williams College and lead author of the study.

“We had been studying these sites for a number of years, and realised that this was an opportunity to measure the coastal response to very large storm events.”

1-s2.0-S0012825217302350-gr4_lrg Feld photographs of the two largest blocks to have moved on Inishmore. A: Boulder 267, on the lower platform, weighs ≈ 475 t. The yellow box outlines two full-size adults on the upper platform. B: Boulder 293 weighs ≈ 620 t. The white patch marks the previous location of a 60-ton slab that was dislodged during storms.

So in the summer after the storms, Professor Cox and a team of seven undergraduate students from Williams College surveyed 100 sites in western Ireland, documenting with photos the displacement of 1,153 boulders.

They measured the dimensions and calculated the mass of each boulder.

As they knew where 374 of the boulders had come from, for these they also documented the distance travelled.

The largest boulder, at 237-239 m3 was an estimated 620 tons; the second biggest, at 180-185 m3, was about 475 tons. These giant rocks were close to sea level (although above the high tide mark). At higher elevations, and at greater distances inland, smaller boulders moved upwards and inland.

The boulders are usually created quite near to where they are deposited.

Thus boulder creation generally happens quite close to the site of deposition, so although clasts are deposited in many cases quite far inland and well above the high water mark, net transport distances are often not that large.

Previous studies seemed to indicate that storm waves couldn’t move or deposit boulders that large or too high above sea level. But this research shows that this isn’t always the case.

Their analysis showed that the waves had most power at lower elevations and closer to the shore. They say that while this may not be surprising, “the sheer energy of the waves and their ability to move such large boulders was – and this evidence proves that not only tsunami but also storm waves can move such large objects”.

Cox added: “Now that we know what storm waves are capable of, we have much more information for policy makers who are responsible for preparing coastal communities for the impact of high-energy storms.”

Read: ‘In Boston they’d throw you in the clink’: Here’s why you should never drive in a blizzard>

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    Mute Séamus
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    Mar 2nd 2018, 6:59 AM

    I like that boulder.

    That is a nice boulder.

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    Mute Dan
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    Mar 2nd 2018, 8:32 AM

    @Séamus: Donkey!!

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    Mute Derek O'Sullivan
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    Mar 2nd 2018, 10:22 AM
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    Mute Hugh Corcoran
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    Mar 2nd 2018, 7:47 AM

    40% of the worlds population live within 100 meters of the sea!! I understand most cities are on coasts, but only a small amount of people are with 100 meters. Anyone else think this stat seems a bit off.

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    Mute Lad
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    Mar 2nd 2018, 7:53 AM

    @Hugh Corcoran: miles maybe

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    Mute Walt Jabsco
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    Mar 2nd 2018, 6:39 AM

    Any Aran Islander could have told them that.

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    Mute BlueSkyThinking
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    Mar 2nd 2018, 8:02 AM

    @Walt Jabsco: pity they didn’t then!

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    Mute Walt Jabsco
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    Mar 2nd 2018, 7:46 PM

    @BlueSkyThinking:
    Were they asked?

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    Mute john aherne
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    Mar 2nd 2018, 8:23 AM

    Think of all that energy. Quick put in wave harnessing technology and let’s sell the rights to some other country and spend the rest of our lives paying thru the nose for it

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    Mute James Darby
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    Mar 2nd 2018, 6:47 AM

    So it wasn’t the fairies after all.

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    Mute stephen
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    Mar 2nd 2018, 8:29 AM

    “new research shows”. Must take intense scientific research to tell that a boulder that used to be way down there is now all the way up here

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    Mute C_O'S
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    Mar 2nd 2018, 10:30 AM

    I look at the massive boulders on the mountain tops and it always makes me wonder how and when they got there or was it all down to the ice age. It’s always a ground me moment regarding time.

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    Mute James Doyle
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    Mar 2nd 2018, 12:19 PM

    @C_O’S: Mount Everest was under a sea at one stage in our planets evolution, fish fossils have been found on the top of Everest. Ireland was down at the equator at one stage until continents drifted apart over many millions of years, and it is still happening but so slowly we barely notice.

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    Mute David Dickson
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    Mar 2nd 2018, 12:57 PM

    @James Doyle: and on the third day He created……

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    Mute James Doyle
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    Mar 2nd 2018, 2:53 PM

    @David Dickson: Now now don’t upset the delusional God squad.

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    Mute Sean
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    Mar 2nd 2018, 11:11 AM

    It’s an interesting study that adds to the work of previous studies. Of course, anecdotally everyone knows about boulders the “size of cars” that were moved but it’s necessary to take a more scientific approach. Superstorms are believed to accompany global warming which is why studies like this are of great interest.
    http://www.independent.co.uk/environment/megastorms-that-can-throw-thousand-tonne-boulders-up-cliffs-may-be-on-their-way-back-thanks-to-a6754511.html

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    Mute John Considine
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    Mar 2nd 2018, 3:37 PM

    @Sean: at Ballyreen on the coast of North Clare, the day after the big storm in 1988, it was obvious that boulders the size of forty foot truck containers and bigger had been moved around by the sea the night before, because they left long scratch marks. Nothing new here for me.

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    Mute Michael Kehoe
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    Mar 3rd 2018, 5:59 AM

    Bigger and Boulder

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    Mute The IMF are here
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    Mar 3rd 2018, 8:01 AM

    And I bet you some clown though it was a good idea to go for a swim in the seat that day!

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