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Hunga Tonga volcano spewed ash 36 miles high, a world record

It blasted into the mesosphere, the third layer of Earth’s atmosphere

The eruption of Hunga Tonga as seen from the Himawari satellite. (NASA) (NASA)
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NASA has confirmed that the Jan. 15 eruption of Hunga Tonga, an underwater volcano in the southwest Pacific, spewed ash 36 miles high into the atmosphere. That staggering figure sets a world record and indicates that volcanic material made it into the third layer of Earth’s atmosphere — the mesosphere.

How the Tonga volcano generated a shock wave around the world

The agency called it “likely the highest plume in the satellite record,” surpassing what many volcanologists and atmospheric scientists had known was physically feasible. The findings open the door to new studies on the dynamics of volcanoes and the mechanisms of transport of the particles, or aerosols, they emit.

The eruption of Hunga Tonga produced a tsunami that devastated parts of Tonga and even reached the U.S. Pacific coastline. Sound from the volcano’s explosive eruption was heard more than 5,000 miles away in Alaska, and air-pressure perturbations rapidly radiating outward from the volcano were picked up by weather stations around the globe.

What are volcanic plumes?

When a volcano erupts, it releases ash, smoke, steam, heat, gases and fine particulates into the atmosphere. The exceptional amount of heat within the plume causes it to rise. Air will ascend so long as it is warmer than its surroundings. As a plume entrains cooler air from the surrounding environment, its upward motion tends to slow.

Ordinarily, thunderstorm and volcanic plumes alike tend to flatten out at the tropopause, or the “ceiling” of the lower atmosphere marking the threshold of the stratosphere. In the stratosphere, air temperature increases with height, making a warm layer that’s impenetrable to most updrafts. Only the hottest or most explosive and dense plumes are able to puncture the tropopause.

Those plumes tend to be responsible for the injection of volcanic particles into the stratosphere. Sulfur dioxide and other aerosols that make it into the stratosphere can have bearings on Earth’s climate, as well as influence the color of sunrises and sunsets.

Hunga Tonga’s plume

Using data from the GOES-17 weather satellite and the Japanese satellite Himawari-8, which operate in “geosync” at 22,236 miles above Earth’s surface, scientists at NASA’s Langley Research Center were able to estimate the height of Hunga Tonga’s plume.

Using multiple satellite sources viewing the plume from different angles, it was possible to ascertain the approximate height of the plume. That’s commonly referred to as a “parallax” effect.

“From the two angles of the satellites, we were able to recreate a three-dimensional picture of the clouds,” said Konstantin Khlopenkov, a scientist on the NASA Langley team, in the NASA news release.

Ordinarily, calculating the height of the plume could have been achieved with only one satellite. As long as it was able to sense cloud top temperatures, meteorologists would have been able to make comparisons with data obtained from weather balloons and other estimates of the environment. It would have been a simple game of matching numbers — but Hunga Tonga’s plume soared higher than weather balloons.

How high did it get?

After careful inspection, it was determined that the plume soared 36 miles high — three times as tall as the most violent tornado-producing thunderstorms and 14 miles taller than the previous volcanic eruption world record. That was Mount Pinatubo, which erupted in the Philippines in 1991 to a height of 22 miles.

That placed the height of the plume solidly in the mesosphere, above the troposphere and stratosphere. Air temperature decreases with height in the troposphere and increases in the stratosphere; barreling through that comparatively warm stratospheric layer and penetrating the mesosphere is virtually unheard of.

The air in the mesosphere is extremely dry. Air temperature also decreases with altitude. The top of the mesosphere is the coldest part of Earth’s atmosphere; the air there is incredibly thin, and heat is also lost because of radiative emission from carbon dioxide. Meteors burn up in the mesosphere.

Characteristics of the plume

The plume had so much upward momentum in rising that it couldn’t “put the brakes on” when it came time to stop rising, resulting in a bubbling lump known as an overshooting top. The plume immediately subsided after its initial pulse of buoyancy, which created an undulating bobber-like motion that sent ripples known as “gravity waves” outward. Those ripples propagated through the ionosphere, a layer of Earth’s atmosphere rich in ions and free electrons which overlaps the mesosphere and thermosphere (the next layer up).

The plume sparked prolific lightning, producing 200,000 lightning strikes in just an hour’s time. It was the tallest thunderstorm ever directly observed on Earth. According to NASA, a staggering 60,000 square miles was covered by the resulting plume cloud, an area the size of Georgia.

The effects of the eruption are still being studied, but NASA reports material from the volcano had completed a full revolution around Earth in the Southern Hemisphere’s atmosphere within the first two weeks following the eruption. It does not appear that a sufficient quantity of sulfur dioxide was released to cool Earth’s climate.

correction

In previous versions of this post, the headline and first paragraph incorrectly said the Hunga Tonga plume reached 38 miles into Earth's atmosphere. The correct figure is 36 miles. This post has been corrected.

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