San Diego Union-Tribune (Sunday)
TONGA VOLCANO SPEWED ASH 38 MILES HIGH, A WORLD RECORD
Global effects of January eruption still being studied
NASA has confirmed that the Jan. 15 eruption of Hunga Tonga, an underwater volcano in the southwest Pacific, spewed ash 38 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.
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.
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.
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 done 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.
After careful inspection, it was determined that the plume soared 36 miles high — three times taller than 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 plume sparked prolific lightning, producing 200,000 lightning strikes in just an hour’s time.
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.