When an underwater volcano erupted near the small, uninhabited island of Hunga Tonga-Hunga Ha‘apai in January 2022, two weather satellites were uniquely positioned to observe the height and breadth of the plume. Together they captured what is likely the highest plume in the satellite record.
Scientists at NASA’s Langley Research Center analyzed data from NOAA’s Geostationary Operational Environmental Satellite 17 (GOES-17) and the Japanese Aerospace Exploration Agency’s (JAXA) Himawari-8, which both operate in geostationary orbit and carry very similar imaging instruments. The team calculated that the plume from the January 15 volcanic eruption rose to 58 kilometers (36 miles) at its highest point. Gas, steam, and ash from the volcano reached the mesosphere, the third layer of the atmosphere.
Prior to the Tonga eruption, the largest known volcanic plume in the satellite era came from Mount Pinatubo, which spewed ash and aerosols up to 35 kilometers (22 miles) into the air above the Philippines in 1991. The Tonga plume was 1.5 times the height of the Pinatubo plume.
“The intensity of this event far exceeds that of any storm cloud I have ever studied,” said Kristopher Bedka, an atmospheric scientist at NASA Langley who specializes in studying extreme storms. “We are fortunate that it was viewed so well by our latest generation of geostationary satellites and we can use this data in innovative ways to document its evolution.”
The animation above shows a stereo view of the Tonga eruption plume as it rose, evolved, and dispersed over the course of 13 hours on January 15, 2022. The animation was built from infrared observations acquired every 10 minutes by GOES-17 and Himawari-8. According to these observations, the initial blast rapidly rose from the ocean surface to 58 kilometers in about 30 minutes. Shortly afterward, a secondary pulse rose above 50 kilometers (31 miles), then separated into three pieces.
Typically, atmospheric scientists calculate cloud height by using infrared instruments to measure a cloud’s temperature and then comparing it with model simulations of temperature and altitude. However, this method relies on the assumption that temperatures decrease at higher altitudes—which is true in the troposphere, but not necessarily in the middle and upper layers of the atmosphere. The scientists needed a different method to calculate the height: geometry.
Hunga Tonga-Hunga Ha‘apai is located in the Pacific Ocean roughly midway between Himawari-8, which is in geostationary orbit at a longitude of 140.7° East, and GOES-17, in geostationary orbit at 137.2° West. “From the two angles of the satellites, we were able to recreate a three-dimensional picture of the clouds,” explained Konstantin Khlopenkov, a scientist on the NASA Langley team.
This sequence of still images from GOES-17 shows the plume at various stages on January 15. Note how the tallest parts of the plume in the stratosphere and mesosphere cast shadows down on the lower parts.
Khlopenkov and Bedka used a technique that they originally designed to study severe thunderstorms that penetrate the stratosphere. Their algorithm matches simultaneous observations of the same cloud scene from two satellites, and then uses stereoscopy to construct a three-dimensional profile of elevated clouds. (This is similar to the way the human brain perceives things in three dimensions using two images from our eyes.) Khlopenkov then verified the stereoscopic measurements using the length of the shadows that the tallest plumes cast on the broad ash clouds below. They also compared their measurements with a NASA GEOS-5 model analysis to determine the local height of the stratosphere and troposphere that day.
The uppermost part of the plume sublimated almost immediately due to extremely dry conditions in the mesosphere. However, an umbrella of ash and gas spread out in the stratosphere at an altitude of about 30 kilometers (20 miles), eventually covering an area of 157,000 square kilometers (60,000 square miles), larger than the state of Georgia.
Aerosols from the plume have persisted in the stratosphere for nearly a month after the eruption and could stay for a year or more, said atmospheric scientist Ghassan Taha of NASA’s Goddard Space Flight Center. Volcanic emissions can potentially affect local weather and global climate. However, Taha noted that it currently seems unlikely the Tonga plume will have significant climate effects because it was low in sulfur dioxide content—the volcanic emission that causes cooling—but high in water vapor, which accounts for its impressive height.
“The combination of volcanic heat and the amount of superheated moisture from the ocean made this eruption unprecedented. It was like hyper-fuel for a mega-thunderstorm,” said Bedka. “The plume went 2.5 times higher than any thunderstorm we have ever observed, and the eruption generated an incredible amount of lightning. That is what makes this significant from a meteorological perspective.”
For more than a decade, an undersea volcano has been erupting in the South Pacific near Tonga. The eruptions created a new island near Hunga Tonga and Hunga Ha'apai; then a potent blast wiped out the island in early 2022.