If you could travel to the ocean floor, near tectonic plate boundaries, you might see the glow of lava spewing from an erupting deep-sea volcano. It would be the only light source around, illuminating cracks in the ocean floor and huge ejections of hot fluid with billowing clouds of volcanic rock fragments.
Those ejections are called megaplumes — massive columns of hot, chemical-rich water with volumes that can exceed 40 million Olympic swimming pools. And they are powerful. New research, published in Nature Communications, suggests one deep-sea eruption could create a megaplume with enough power to juice the continental United States for the duration of the eruption.
During an eruption, the U.S. consumes about as much energy as a megaplume produces. Hypothetically, one eruption could supplant the energy used during this period.
“You could ‘keep the lights on,’ so to speak, in the whole of the U.S. using the energy output from just one eruption, but only for the duration of that eruption — let’s say 10 to 20 hours,” says co-author David Ferguson, a volcanologist at the University of Leeds. “It’s a bit like turning a massive power station on and then off.”
“It’s a bit like turning a massive power station on and then off.”
How the discovery was made — To get to this finding, Ferguson and fellow co-author Sam Pegler utilized data from a 2009 study where researchers in California deployed remotely operated vehicles to the seafloor. These rovers collected a bunch of tephra samples (volcanic rock fragments) that all likely came from the same eruption.
Using data on where the tephra was distributed, Ferguson and Pegler created math models to calculate how powerful a megaplume would need to be to achieve that kind of spread — kind of like observing the spread of confetti to find the power of a confetti cannon.
“That’s, on the surface level, a great analogy,” says Pegler. “Except the thing that's driving the eruptive transport of tephra is heat and buoyancy. So it's more like convection from a radiator, whereas confetti is driven by momentum or inertia.”
Pegler says they ruled out other mechanisms of tephra spread, like ocean currents and tides, which didn’t fit their models. The most logical explanation, he says, is a megaplume-driven heat transfer that creates huge convection cycles in the water with 1 to 2 terawatts of power. For comparison, New York City uses 52 terawatt-hours of energy in one year, meaning it would take one of these megaplumes 26 to 52 hours to generate the city’s energy for the year (though, these megaplumes do not last for that long).
That’s a massive amount of power, and a result the scientists didn’t expect.
“At first we just dismissed it, because we thought it was wrong,” says Ferguson. “It was too high.”
The hunt for alternative sources of energy
The idea that just one megaplume could generate enough power to meet the energy needs of the U.S. is pretty incredible, but Ferguson says the comparison is just illustrative — “we’re not proposing some unusual new form of geothermal energy.”
But using hydrothermal vents for electricity generation is a dream other scientists are chasing.
For decades, the possibility of harnessing the Earth’s heat as an energy source at the ocean floor has been tantalizing researchers as a possible clean energy solution. The Earth’s crust at the bottom of the sea is thinner than it is on continental land, and any machinery there wouldn’t need to obstruct any human habitats.
In a 2008 report by the Department of Energy, for example, scientists assessed the potential of ocean crust energy harvesting and found that the heat stored in the ocean floor, at depths between 3 to 10 kilometers, is so great that harvesting just 2 percent of that energy could result in more than 100,000 megawatts. Other scientific proposals have been published, suggesting the possibility and potential of concepts like offshore structures that combine wind turbines and deep-sea heat exchangers — which would combine wind and heat energy to generate electricity. So far, however, none of these projects have come to fruition.
Practically, deep-sea volcanic eruptions as electricity aren’t an option — for now. “This has all the attributes that you would not want in an energy source,” Ferguson says. “[A megaplume] is extremely intermittent and it's extremely inaccessible.”
Megaplumes, Ferguson adds, are also extremely difficult to both predict and find. By the time scientists can identify one, it’s already hundreds of cubic kilometers in size, meaning the heat has already diffused significantly, making any energy extraction basically impossible. Add in the fact that these happen thousands of miles away from any human-populated land, and you can see where the logistics break down.
Even if you could predict where a megaplume will crop up, says Ferguson, you’d either need a huge, ridiculously long cable, or some sort of massive battery on a ship to take that power to shore. Ultimately, “I think it would cost you more to extract any energy than you would get back,” he says.
Regardless of whether we can harvest the power of megaplumes, what’s certain is that this research advances scientists’ understanding of submarine volcanoes, which make up 80 percent of all eruptive activity. This research brings scientists one step closer to unveiling the secrets of the ocean floor — and points to a tantalizing hypothetical humans don’t yet know how to harness.