MONSTROUS oceanic waves are able to transport boulders weighing hundreds of tonnes. The finding helps explain . It also implies that storm waves, and other rogue waves, can be more powerful and hazardous than previously thought.
Until recently, the heaviest rock known to have been transported by waves was about 200 tonnes. Now of Williams College in Massachusetts and her colleagues have found a new record holder: a 620-tonne boulder, equivalent to roughly .
Cox found the boulder on the west coast of Ireland. The region was struck by a huge cluster of storms during the winter of 2013-2014. When she and her team examined photographs taken before and after the storms, they found the massive boulder had been moved about 2.5 metres (, ).
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Many researchers didn鈥檛 think such heavy boulders could be moved by storm waves, says Cox. 鈥淐alculations and force-balancing equations suggested that storm waves did not have sufficient power, so there were people who argued strongly that only tsunamis were capable of moving such huge blocks,鈥� she says.
However, advances in buoy technology are yielding more detailed measurements of storm waves, and we now know they can generate huge forces. 鈥淚t鈥檚 fun to show that these giant boulders were moved around during storms, and to imagine the wild energy of the waves,鈥� Cox says.
However, perhaps the most important part of the new work is its application to assessing wave hazards to coastal areas.
The team charted not only the biggest boulders, but also the distribution of more than a thousand smaller boulders at many sites along Ireland鈥檚 western coast. Cox says the pattern of boulder movements is a guide to the kinds of wave forces that Ireland鈥檚 coast, and others like it, might face during future storms.
In December, Ireland鈥檚 Environmental Protection Agency suggesting that storms may become more intense because of climate change. Knowing just how powerful waves can be may prove vital for protecting inhabited coastlines.
鈥淎 wave that can move a 600-tonne rock can also move anything else that鈥檚 600 tonnes,鈥� says Cox . 鈥淎nd if storminess increases, as it may well with climate change, then that kind of wave power, currently occurring on remote, exposed coastlines, might be coming to coastlines that do not currently experience it.鈥�
鈥淥ne of the greatest challenges we face is the increasing flood and erosion risk to rural coastal communities and the need to provide them with sustainable protection strategies,鈥� says geographer at the National University of Ireland Galway. 鈥淚 feel very strongly about this, especially when coastal areas are what make places like Ireland unique.鈥�
Cox says it is unlikely the 620-tonne boulder is the biggest object that ocean waves can move. There are boulders in the study area that are even heavier and they bear signs of wave transport. However, they didn鈥檛 move during the storms in question, so we don鈥檛 yet have definitive evidence that waves can move them.
This article appeared in print under the headline 鈥淟et the boulders fall where they may鈥�
