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Breakneck Outflows from Earth’s Most Explosive Eruption

• Physics 16, 159

The 2022 eruption of {a partially} submerged volcano close to Tonga produced ejecta that hurtled at 122 kilometers per hour—as decided by timing the following rupture of a seafloor cable.


An eruption of an underwater volcano close to Tonga launched ejecta that destroyed communication cables 100 km from the blast website.

On January 15, 2022, Earth skilled its most explosive volcanic eruption in 140 years at Hunga Tonga–Hunga Haʻapai, {a partially} submerged volcano within the Pacific Ocean close to the Kingdom of Tonga’s foremost island. Now Michael Clare and Isobel Yeo of the UK’s Nationwide Oceanography Centre and their colleagues have decided the utmost pace of the underwater rock flows related to this occasion [1]. Their research constitutes essentially the most detailed investigation into the underwater aftermath of a robust volcanic eruption and opens a brand new window onto a broad class of particle-laden flows.

The eruption at Hunga Tonga–Hunga Haʻapai hurled greater than 6 km3 of particles as much as a peak of 57 km. When that ejecta plunged again to Earth, a few of it struck the volcano’s steep underwater slopes, launching torrents of water-entrained sediment outward throughout the seafloor. Seven minutes after the preliminary eruption, Tonga misplaced its web connection to the remainder of the world, an occasion that Clare, Yeo, and their colleagues used to infer the pace at which the entrained materials moved.

This “breaking-of-a-seafloor cable” technique for figuring out materials move speeds made its debut in 1929. A big earthquake triggered an underwater landslide off the coast of Newfoundland, Canada, that sequentially broke all of the telegraph cables that linked the US to Europe at the moment. Then in 1979, the tactic was once more used when, throughout its development, an extension to Good Côte d’Azur Airport, France, collapsed into the Mediterranean Sea. The pace of the Newfoundland and Good flows, and others measured in the identical manner since, have been considerably decrease than Hunga’s, which was each quick and intensive: when the analysis crew surveyed the seafloor after the eruption, they discovered newly deposited materials so far as 100 km from the volcano. This materials got here from the three km3 of sediment that the flows lower and scoured within the rapid neighborhood of the volcano. Such was the amount of eliminated materials, some sections of Tonga’s web cable have been left buried beneath 22 m of rubble.

The fabric zooming down Hunga’s slopes and throughout the seafloor moved in what resembled a pyroclastic density present (PDC). Noticed on land, PDCs come up when scorching ejecta—rock, ash, and fuel—lose their buoyancy and move down a slope beneath gravity. Clare stresses that the flows at Hunga are completely different from PDCs in that they have been created when giant fluxes of erupted, dense volcanic materials collapsed vertically into the ocean. This inception mechanism—direct entry of pyroclastic materials into the ocean—was beforehand undocumented, Yeo says, which explains the novelty of observing such outstanding move speeds.

The documentation of this new inception mechanism is a key end result of the research, says Michael Manga of the College of California, Berkeley, who spent this previous winter finding out submarine volcanism within the Aegean Sea. “[The study] exhibits that the eruption column collapsed to feed submarine flows, that these flows travelled quick and a good distance, and that we’ve estimates of the amount that erupted,” he says.

APS/Carin Cain

Flung excessive into the ambiance, ejecta from the January 2022 eruption of Hunga Tonga–Hunga Haʻapai plunged again to Earth, hurtling down the volcano’s steep sides, and launching particle-carrying flows that have been quick, far-reaching, and damaging.

Moreover encompassing vast ranges of temperature and composition, density currents equivalent to these at Hunga are additionally turbulent and change vitality and momentum with the encompassing fluid and the underlying floor. What’s extra, the currents can transition from extraordinarily dense flows of granular particles to dilute discharges of absolutely turbulent suspensions. Stream phases can coexist and alter over time. Thus, the crew says, the findings add to the understanding of the variety and complexity of the particulate flows, which embrace among the largest floods, avalanches, and gravity currents on the planet. That data is essential for enhancing predictions of the impacts of main environmental hazards on infrastructure and society.

Though the 2022 Hunga eruption was unusually violent, it was among the many 80% or so eruptions whose penalties play out partially or wholly underwater. Some new undersea cables will inevitably cross volcanically energetic areas. Yeo says that the brand new outcomes from the analysis crew point out the necessity to determine submerged volcanoes that would threaten such cables and, extra broadly, to begin monitoring these underrecognized hazards.

–Charles Day

Charles Day is a Senior Editor for Physics Journal.


  1. M. A. Clare et al., “Quick and damaging density currents created by ocean-entering volcanic eruptions,” Science 381, 1085 (2023),

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