How the most intense storm ever observed appeared – 07/22/2023 – Science

In the South Pacific Ocean there are two small islands, whose dark rock contrasts sharply with the blue water that laps their edges.

While apparently nothing special, they are all that remains of a huge underwater volcano, the Hunga Tonga-Hunga Ha’apai.

The islands are actually small peaks on the edge of a large caldera-shaped cavity that is their crater.

The volcano erupted violently in January 2022, spewing 10 cubic kilometers of rock, ash and sediment and producing a plume 58 km high.

It was the largest atmospheric explosion recorded by modern instruments.

The huge volcanic cloud covered the region and was so big that astronauts in orbit aboard the International Space Station could see it.

The eruption triggered a megatsunami with waves up to 45 meters high, devastating the islands of Tonga and wreaking havoc as far away as Russia, Hawaii, Peru and Chile.

At least six people died in the tsunami, two in Peru.

But the explosion and tsunami weren’t the only record-setting events caused by the volcano’s eruption. It also caused the most intense lightning storm ever seen.

“It’s an eruption of superlatives,” says Alexa Van Eaton, a volcanologist with the US Geological Survey, who led a study of the extraordinary electrical activity within the ash cloud produced by the Hunga Tonga-Hunga Ha’apai.

The supercharged storm was tracked from space by satellites, offering an unrivaled view of the lightning bolts high up in the volcanic plume.

And the lightning’s fury was “like no one has ever seen,” says Van Eaton, providing valuable new information about the volcano and what happened during the eruption.

An unprecedented storm

At its height, the thunderstorm caused by the volcanic plume over Hunga Tonga-Hunga Ha’apai produced 2,600 lightning strikes per minute.

Nearly 200,000 lightning bolts illuminated the interior of the dark ash cloud for 11 hours.

Bright bursts of electrical discharges rose 20-30 km above the ocean, forming some of the highest altitude lightning strikes ever recorded.

“Having lightning in the stratosphere is very unusual,” says Van Eaton.

Volcanic lightning is not uncommon.

The earliest account we have of them is by the Roman lawyer and writer Pliny the Younger, who, in a letter to a friend, described “zigzag lightning” that accompanied the eruption of Mount Vesuvius that destroyed Pompeii in AD 79

But it was the amount of lightning generated that surprised scholars about volcanoes.

“It’s more than we’ve seen anywhere on the planet, including supercells,” says Peter Rowley, a physical volcanologist at the University of Bristol in the UK.

Supercells are a severe form of thunderstorm that bring intense lightning, extreme rainfall, and even hail.

The electrical storm in the Hunga Tonga-Hunga Ha’apai volcanic plume was so intense that terrestrial radio antennas thousands of kilometers away picked up the activity.

The researchers believe the storm developed because the highly energetic magma ejected through the shallow ocean.

The molten rock vaporized seawater, which was uplifted with the column of ash and debris.

The eruption spewed over 146 million tons of water vapor into the Earth’s stratosphere, adding 10% to the amount of water in just a few days.

NASA (the American space agency) later reported that the volume of water was enough to fill the equivalent of 58,000 Olympic swimming pools. Water vapor reached the mesosphere, one of the upper layers of the atmosphere.

The interaction between volcanic ash, water molecules and ice particles in the plume, which formed when water droplets supercooled in the upper atmosphere, generated large electrical charges – producing the perfect conditions for lightning.

“It turns out that volcanic eruptions can create more extreme lightning than any other type of storm on Earth,” says Van Eaton.

But it wasn’t just the intensity of the ray that intrigued Van Eaton and his colleagues.

Concentric rings of rays, centered on the volcano, expanded and contracted in the plume over time.

“The scale of these ray rings surprised us,” he says.

“We’ve never seen anything like this before, there’s nothing comparable in weather storms. Single rings of lightning were observed, but not multiple ones, and they were small by comparison.”

The researchers believe that what was responsible for this was the intense high-altitude turbulence created by the volcanic explosion.

The large amount of material released by the volcanic eruption quickly reached its maximum height and expanded to create an umbrella cloud more than 300 km wide.

The thrust generated by the explosion caused the material in the plume to continue to “overshoot” the stratosphere, generating fast-moving concentric waves known as gravity waves. It was a bit like throwing pebbles into a pond.

The lightning appeared to “surf” on these waves and expanded outwards in a 250km ring pattern.

“Seeing that the lightning rings formed, or at least associated with, gravity waves moving through the cloud was really impressive to us,” says Van Eaton.

It was the first time the data demonstrated how a powerful volcanic plume can create its own weather system, maintaining the conditions for electrical activity at previously unobserved heights and rates.

“It’s possible that in very large eruptions, these kinds of concentric growth rings – these gravitational waves from ash – are followed by lightning, perhaps more than we think,” says Rowley, who was not involved in Van Eaton’s study.

But the scientist says that more data is needed to be sure about the fact.

revealing show

The lightning provided more than a stunning light show: it helped reveal details about the Hunga Tonga-Hunga Ha’apai eruption.

Lightning data collected through a combination of satellite imagery and data from a terrestrial radio antenna showed that the volcano’s behavior can be divided into four distinct phases of activity.

Lightning rates rose and fell as plume height changed.

It started with a very small plume, “so faint that no one had noticed it,” explains Van Eaton.

Then, in phase two, the plume began to rise from an eruption of much greater intensity over the course of several hours, spewing a large amount of rock, ash and sediment into the air – the equivalent of the amount of rock needed to build the Great Pyramid of Giza 3,800 times.

In phase three, the eruption continued at a lower intensity and the height of the plume dropped to around 20 to 30 km high, which “is still extraordinary”, says Van Eaton.

Then there was an intriguing lull as the volcano apparently took a break, he explains, before phase four saw the eruption lessening in ferocity over time.

“Being able to unravel this last gasp of the climate phase is really useful for anyone who needs to predict ash emissions and their transport through the atmosphere,” says Van Eaton.

‘underestimated’ risk

In the days following the eruption, the massive ash plume produced by Hunga Tonga-Hunga Ha’apai was blown by winds about 3,000 km west of Australia.

Ash can affect water supplies and hamper relief efforts.

It can also be extremely expensive for airlines: Iceland’s 2010 Eyjafjallajökull volcano, for example, cost the airline industry an estimated $1.4 billion.

It is currently difficult to obtain reliable information on volcanic plumes at the onset of an eruption, especially for remote undersea volcanoes.

But the Hunga Tonga-Hunga Ha’apai data can help meteorologists monitor and provide short-term forecasts of hazards to aviation from explosive volcanism, including the development and movement of ash clouds.

Understanding this is vital, as scientists say an eruption on the scale of Hunga Tonga-Hunga Ha’apai is likely to occur again.

This threat is driving collaboration among researchers.

David Tappin, a volcanic tsunami expert at the British Keyworth Geological Survey and former chief geologist for the Kingdom of Tonga, warns that the unexpected nature of the Hunga Tonga-Hunga Ha’apai eruption highlights that the global danger of large volcanic eruptions is underestimated.

There are approximately 42 volcanoes around the world with the potential to cause an eruption as spectacular as Hunga Tonga-Hunga Ha’apai, says the expert.

And he says the record eruption should serve as a wake-up call to better prepare.

“This eruption had such a global and far-reaching impact that we are all starting to reorganize the way we communicate,” adds Van Eaton.

There were weeks of feathers at lower levels before the Hunga Tonga-Hunga Ha’apai “went crazy”, she says.

“It shows that even a very ordinary eruption can change course at any time, and there really isn’t an easy way to predict that.”

This article was originally published on BBC Future. To read the original version (in English), Click here.