Scientists have discovered a way to tap into the ocean’s vast, untouched energy reserves – but should they?
From seawalls to early-warning systems, countries worldwide have invested billions into safeguarding their coastlines from the devastating power of tsunamis. But as the tsunami that struck Japan on 11 March 2011 demonstrated, even the best mitigation efforts can be overwhelmed. The unprecedented height of the waves that followed the Tōhoku earthquake – some reaching more than 25 metres – simply washed over or destroyed seawalls at Taro, Kamaishi and Fukushima. Instead, what if we could stop tsunamis before they reach the coast?
The idea may sound like science fiction, but Usama Kadri, a mathematician at Cardiff University, suggests it might just be possible. In fact, he and his team have provided a compelling proof of concept.
Kadri’s work focuses on something called acoustic–gravity waves (AGWs), which are generated by events such as earthquakes or volcanic eruptions, sometimes occurring thousands of metres beneath the ocean’s surface. These AGWs travel by compressing and expanding the water – similar to how sound moves through the air. Unlike waves on the ocean surface, which travel at tens of metres per second, deep-sea sound waves travel at thousands of metres per second. Kadri emphasises that these two types of waves are totally different, but his research reveals that, sometimes, they interact – a phenomenon known as triad resonance.
Imagine three musical notes playing together. If their frequencies and wavelengths align in a very specific way, they can resonate, transferring energy between them. Ocean waves – whether it’s two surface waves and an AGW, or two AGWs and a surface wave – can similarly exchange energy between themselves under the right conditions. ‘It’s almost like a dance,’ says Kadri. He suggests that by strategically directing two engineered AGWs at an oncoming tsunami, we could tune into its resonant frequency, allowing the AGWs to absorb and redistribute the tsunami’s immense energy over a vast area – significantly reducing its height and destructive power before it ever reaches coastal communities.
While the concept of generating such powerful and precisely tuned AGWs in the deep ocean presents a significant engineering challenge, Kadri and his colleagues have proved that, in a lab setting, the theory works. They have also discovered that, just as two AGWs can be used to suppress surface waves, they can also amplify them. ‘For example, if you sent two AGWs at the wrong time in the surface wave’s cycle, you could end up feeding the tsunami rather than reducing it,’ he says. While this adds to the complexity of mitigating this natural hazard – for now, we simply don’t have enough accurate, real-time data on the properties of any one tsunami to be able to match wave frequencies – it does introduce another possibility: renewable wave power.
‘Tsunamis are one thing – wave power is something very different,’ says Kadri. Not only are they on completely different scales, he explains, you can actually observe waves in real time. ‘We have all the data we need to finely tune the waves for this interaction.’ The discovery could make wave power – which is yet to be developed in the same way as wind and solar – a new avenue for clean, renewable energy.
Ocean waves represent a vast, untapped source of energy, producing an estimated 50 trillion to 80 trillion watts of power worldwide – nearly two to three times the world’s current annual energy consumption. However, current technologies often struggle to efficiently capture this energy, especially in deep water. By using AGWs to amplify surface waves, we could potentially make wave energy harvesting far more effective.
Kadri’s research suggests that using triad resonance could increase surface wave heights by more than 30 per cent. He even believes it could be used to power the generation of AGWs, minimising carbon emissions throughout the process and ensuring that the least amount of energy possible goes to waste. His next steps are to produce further numerical simulations and conduct a series of small-scale laboratory experiments to determine the best way to scale up future technology, with a view to turning it into a commercial reality.
Nonetheless, Kadri cautions that we ought to be careful. ‘People often say that the energy created by waves goes to waste,’ he says. ‘We need to be cautious about making such statements. The fact that we don’t know where that energy goes and how it circulates later on doesn’t mean it’s wasted.’ There are many oceanic processes – such as how nutrients and carbon are transported – that we still don’t fully understand. ‘Maybe we’d be getting loads of energy for free, but maybe we’d be harming the ocean.’
