The Hunga Tonga volcano spewed ash a record 38 miles into the atmosphere

The Hunga Tonga eruption produced a tsunami that devastated parts of Tonga and even reached the US Pacific coast. The sound of the volcano’s explosive eruption was heard more than 5,000 miles away in Alaska, and atmospheric pressure disturbances radiating rapidly outward from the volcano were picked up by weather stations around the world.

What are volcanic plumes?

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

Ordinarily, stormy and volcanic plumes 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, creating a warm layer impenetrable to most updrafts. Only the hottest or most explosive and dense plumes are capable of perforating the tropopause.

These plumes tend to be responsible for injecting volcanic particles into the stratosphere. Sulfur dioxide and other aerosols that enter the stratosphere can affect the Earth’s climate, as well as influence the color of sunrises and sunsets.

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

By using several satellite sources viewing the plume from different angles, it was possible to determine the approximate height of the plume. This is commonly referred to as a “parallax” effect.

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

Ordinarily, the plume height calculation could have been done with a single satellite. As long as it was able to detect cloud top temperatures, meteorologists could have made comparisons with data obtained from weather balloons and other estimates of the environment. It would have been a simple matching numbers game – but Hunga Tonga’s plume soared higher than the weather balloons.

After careful inspection, the plume was determined to have soared 36 miles high – three times higher than the most severe tornado-producing thunderstorms and 14 miles higher than the previous world record volcanic eruption. It was Mount Pinatubo, which erupted in the Philippines in 1991 at a height of 22 miles.

This placed the plume height solidly in the mesosphere, above the troposphere and stratosphere. Air temperature decreases with altitude in the troposphere and increases in the stratosphere; crossing this relatively warm stratospheric layer and entering the mesosphere is virtually unheard of.

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

Plume characteristics

The plume had so much upward momentum as it rose that it could not “put on the brakes” when it stopped rising, resulting in a bubbling mass known as an overflowing top. The plume immediately calmed down after its initial buoyant impulse, creating a rippling bobber-like motion that sent ripples called “gravity waves” outward. These ripples propagated through the ionosphere, a layer of the Earth’s atmosphere rich in ions and free electrons that overlaps the mesosphere and the thermosphere (the next layer).

The plume unleashed prolific flashes, producing 200,000 flashes in just one hour. It was the largest thunderstorm ever observed directly 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 under investigation, but NASA reports that material from the volcano completed a full revolution around the Earth in the Southern Hemisphere’s atmosphere within the first two weeks of the eruption. It does not appear that enough sulfur dioxide has been released to cool the Earth’s climate.

correction

In previous versions of this article, the title and first paragraph incorrectly stated that the Hunga Tonga plume had reached 38 miles into Earth’s atmosphere. The correct figure is 36 miles. This message has been corrected.

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