Prof Rónadh Cox of Williams College has seen first-hand how giant boulders weighing hundreds of tonnes can be dislodged by powerful storm waves.
After obtaining her bachelor’s degree in science from University College Dublin (UCD) in 1985, Prof Rónadh Cox undertook a PhD at Stanford University where she met her husband and fellow geologist Mark Brandriss.
Spending two years in South Africa, the pair moved back to the US working at the Illinois Urbana-Champaign and eventually Williams College in Massachusetts, where Cox is now a professor of geology and mineralogy.
What inspired you to become a researcher?
I had a geography teacher named Seán Mac Mathúna who delighted in the natural world and because of that I chose geology as a subject at UCD. The first-year lectures given by Dr Pádraig Kennan were also enthralling. I was amazed to discover how active and complicated our planet is, and I wanted to learn more and to understand more.
Can you tell us about the research you’re currently working on?
I examine how storm waves move boulders – and by boulders I mean huge rocks that can be the size of small houses, with the technical term being ‘megagravel’ (I am not making that up!).
The project was inspired by work done by the late Mike Williams from NUI Galway and Adrian Hall at Stockholm University. They documented coastal boulder deposits on the Aran Islands that form ridges several metres high, sitting high above sea level, and tens or even hundreds of metres inland. They were clearly placed there by waves but there was no direct evidence of whether those waves were storm waves or tsunami.
My students and I began surveying the boulders in detail in 2008 and monitoring their locations yearly. Then, in 2013-2014, we got lucky with the ‘North Atlantic storm factory’ when very energetic storms – some with the force of category 3 hurricanes – swept across Ireland’s west coast. When we went back out the following summer, there were extraordinary changes in the boulder deposits.
All our measurements and photographs from the previous years allowed us to make before-and-after comparisons, showing which boulders had moved. Some weighed as much as 600 tonnes, making them the largest boulders ever documented as being dislocated by storm waves.
Others – somewhat smaller at ‘only’ tens of tonnes – were hundreds of metres inland. Even on tops of 26-metre cliffs, boulders weighing several tonnes had been moved around. We also showed that solid bedrock had been ripped up by waves to form new boulders, weighing up to 50 tonnes in some cases. It was incredible to see the scale of change and to think about the sheer power of the ocean.
In your opinion, why is your research important?
These measurements were never made before and show definitively that storm waves move boulders weighing hundreds of tonnes. This is important because previously people argued that these rocks were too big to be moved by storm waves, and that they must have been products of ancient tsunamis. Our observations provide a better understanding of what storm waves are capable of doing at high-energy coastlines.
What commercial applications do you foresee for your research?
Engineers will find our work useful because they want to know the forces to which coastal structures might be subjected, such as piers, seawalls or marine energy installations. As climate changes, with sea levels rising and with the possibility of increased storminess, it is important to properly benchmark the power of coastal waves.
What are some of the biggest challenges you face as a researcher in your field?
Williams College – where I’ve been working for 23 years – is very supportive of research. However, we don’t have a postgraduate programme, meaning all my students are undergraduates. This means that projects have to be designed so that they can be completed in a 12-month period.
The challenge for me is parsing the research questions and data collection so that my students can have a fulfilling research experience and so that, over time, I can build an integrated dataset that addresses the bigger picture.
Are there any common misconceptions about this area of research?
When I talk about boulders that moved on clifftops or far inland, people often envisage them being ripped from the seafloor and cast up to those elevations. That happens sometimes, but only for small boulders. The majority – and all the very large ones – are created on land.
Sometimes, if the wave hits the upper cliff edge in the right way, it can peel back bedrock and shove it inland. At lower elevation, the waves collapse on the shore platform, then surge inland, which can tear up bedrock layers. Most of the time, the boulders are not transported all the way from the ocean; they are made and moved close to the places that we find them.
What are some of the areas of research you’d like to see tackled in the years ahead?
With my colleague Frédéric Dias at UCD and his group of applied mathematicians – and with engineer Pal Schmitt at Queen’s University in Belfast – we are trying to get a better understanding of how waves do the work they do.
We’re also trying to figure out how offshore waves can become amplified in the coastal region so that they can exert these kinds of forces at elevations well above sea level and large distances inland.
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