Irish researchers produce 15,000-year wave map
World-first catalogue provides insight into the deep history of forgotten tsunamis and rogues. Conor Purcell reports.
When reading about maritime history it's always fascinating to imagine the perilous storms and waves which sailors and coastal dwellers experienced throughout the past. Extreme waves, like rogue waves, were once considered the stuff of myth, with surviving sailors returning home to tell tales of their scale.
In fact, it was only in 1995 with the detection of a rogue – the Draupner wave – that the existence of these particular waves was finally confirmed.
Since then, researchers have been attempting to catalogue rogue waves. A major advance came in March this year, with the publication of an interactive map of extreme waves around Ireland, a country that boasts some of the stormiest seas in the world. The map goes back an incredible 14,680 years. It is available on Google Drive.
The map accompanies a paper in the journal Natural Hazards and Earth System Sciences and categorises wave events as either long, including tsunamis and storm surges, or short, including storm and rogue waves.
“The catalogue has been generated from a variety of sources,” says Laura Cooke, a wave energy researcher at University College Dublin, who led the study. “These include past newspaper articles, historical records, scientific reports, databases, and data from various ocean recording devices, like wave buoys and tide gauges.”
Cooke says that events were assessed in different ways depending on their provenance.
“Sources must be approached with a certain degree of caution because they have varying degrees of reliability,” she explains. “For example, a technical report would be considered more reliable than an eyewitness account.”
“Extreme waves occur regularly,” adds co-author Frederic Dias.
“In order to understand how they are generated, and how much damage they can do, it's important to gather all the information we have.
“But it's not so easy. Extreme waves are difficult to observe. You have to be at the right place at the right time.”
To catalogue the waves, the researchers used a number of novel methods. One approach looked at giant boulders deposited on the west coast of Ireland. Judging by their size and location, and coupled with ocean wave modelling, the scientists could determine the nature of the waves which must have moved them there.
The scientists also used information about underwater landslides to infer extreme wave events of the more distant past.
“We have included events dating back thousands of years,” says Cooke. “For example, underwater landslides like the Peach Slide – nearly 15,000 years ago – and the Storegga Slide – over 8000 years ago.”
“Based on numerical models which enact what may have happened at the time of the landslides, the resulting wave heights can be estimated,” she says. “We have analysed the scientific literature that exists for these areas and reported the possible waves that would have reached Irish shores.”
According to the interactive map, the Peach Slide took place around 250 kilometres off the northwest coast of Ireland and may have generated a large-scale tsunami that reached the coast.
Although other catalogues of extreme waves have been generated previously, Cooke believes that this survey represents the first of its kind because it includes entries of both long and short wave types, and for one particular country. A major benefit of the interactive map is that it can be added to over time, acting as a live database, extending events across the world and throughout history.
“We know that this catalogue cannot be an exhaustive list of extreme wave events in Ireland,” says Cooke. “But it provides a benchmark to work from when considering how extreme waves impact the country.”
“This is necessary to inform the future development of Ireland’s marine resources, and to protect the future of coastal communities. But we hope it can also one day contribute towards a global database.”