- It was one of over 1,000 boulders that moved during storms
- Discovery can help interpret how rocks are littered along shorelines
- If seas rise and storms worsen, damage by battering waves will be high
A 620-ton boulder - equivalent in mass to about 90 large African elephants - moved several meters on the island of Inishmore in the winter of 2013-2014 after being slammed by powerful coastal storm waves, according to the research led by Ronadh Cox, a geoscientist at Williams College. It was just one of over 1,000 boulders that moved along Ireland's coasts during the storms, many of them quite large, Cox said. The researchers detected six boulders weighing more than 100 tons and 18 weighing more than 50 tons that had been displaced by waves.
"We had boulders that were north of 100 tons, sitting tens of meters above sea level and tens of meters inland of the high tide mark, that got moved several meters, or several tens of meters," said Cox. "There were boulders that were created from bedrock that were ripped up and disaggregated and the pieces flung into the boulder ridge at 90 meters inland and 50 meters above sea level."
The discovery could help reset our assumptions about how to interpret a variety of mysterious rocks littered along shorelines around the world, which scientists have traditionally linked to powerful tsunami waves. Most prominent among those are a pair of boulders on the Bahamian island of Eleuthrea. The 925-ton and 383-ton rocks sit on a coastal ridge well above sea level. They've been cited as evidence of extreme superstorms occurring more than 100,000 years ago, the last time the planet was as warm as where we're currently headed, and thus interpreted as a lesson about the dangers of climate change. But scientific counterarguments suggest the rocks could have instead been moved by some type of nearby tsunami, and it's hard to know how this debate over ancient events can be fully resolved.
The work by Cox and three colleagues at Williams that was recently published in Earth Science Reviews is more certain. That's because Cox's team knows precisely where these rocks were before they moved and what happened in the area in the brief period between then and now. There were no tsunamis. The scientists had surveyed and photographed rocks up and down the coast of the Aran Islands and other parts of the Irish west coast. So when something moved, they could prove it.
What thus emerges is a landscape that is constantly being transformed and rearranged by waves. The Atlantic-facing coast of the Aran Islands lies up against very deep ocean waters. The islands feature some steep cliffs, as well as gradually sloping rocky shores. Major rock movement was detected in both areas, although clearly it was easier for the ocean to move rocks at lower altitudes.
Further inland on the island of Inishmore there are extensive rock landscapes where boulders and smaller stones pile up in what appears to be a field of debris created by the ocean. "The waves are just surging up these coastal platforms and doing enormous amounts of work at a quarter of a kilometer inland basically," Cox said.
The real question raised by the work, though, is what it says about the future of climate change. If seas rise and storms worsen with a changing climate - as some predict - then understanding the damage that can be wrought by battering waves will be important, Cox said.
"The more intense the storms, the higher the wave energies, so the likelihood of these stronger wave energies hitting in other places becomes greater, as well," she said. "So I think understanding the dynamics of these deposits in these remote areas is going to matter more as energy levels on coastlines around the world tend to increase."
More fundamentally, the work also gives us a picture of the raw power of the ocean, which scientists are only now beginning to measure. "We're still trying to really measure the upper limits of what's possible," said Cox.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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