Hunga Tonga eruption put more than 50B kg of water in the stratosphere

Image of a circular eruption area surrounded by clouds.
in great shape , The Hunga Tonga eruption began underwater, yet erupted directly through most of the atmosphere.

In January of this year, an underwater volcano in Tonga triggered a massive eruption, the largest eruption so far this century. A mixture of hot volcanic material and cold ocean water caused an eruption that sent an atmospheric shockwave across the planet and triggered a tsunami that devastated local communities and reached Japan. The only part of the crater’s rim that protruded above the water became smaller in size and split into two islands. A plethora of material was blasted directly into the stratosphere and mesosphere more than 50 km above Earth’s surface.

We’ve taken a good look at several past volcanic eruptions and studied how they affect the climate. But those eruptions (most notably those of Mount Pinatubo) all came from volcanoes on land. Hunga Tonga may be the largest eruption we’ve ever documented that occurred underwater, and the plume of the explosion contained an unusual amount of water vapor—so much so that it actually got in the way of satellite observations at certain wavelengths . Now, researchers have used weather balloon data to reconstruct the plume and follow its progress during two circuits around the world.

boom meets balloon

is your vocabulary word of the day radiosonde, which is a small instrument package and transmitter that can be carried into the atmosphere by a weather balloon. There are networks of sites where radiosounds are launched as part of weather forecasting services; Most relevant to Hunga Tonga are in Fiji and eastern Australia. A balloon from Fiji was the first to carry instruments to the plume of the eruption, less than 24 hours after the eruption of Hunga Tonga.

That radiosecond saw the water level rising as it climbed through the stratosphere to an altitude of 19 to 28 kilometers. The water level reached the highest level yet measured at the top of that range when the balloon burst, ending the measurement. But shortly after, plumes began to appear along Australia’s east coast, which again recorded high levels of water vapor. Again, the water reached a height of 28 km but gradually reduced to a lower height over the next 24 hours.

The surprising thing was how much of it was there. Compared to normal background levels of stratospheric water vapor, these radioseconds were still recording 580 times more water two days after the eruption, as the plume had some time to dissipate.

There was so much that it still stood out as the plume swept over South America. The researchers were able to track it for a total of six weeks, after which it spread around the Earth twice. Using some of these readings, the researchers estimated the total volume of the water vapor plume and then used the water level present to come up with the total amount of water that was pumped into the stratosphere by the eruption.

They came up with 50 billion kilograms. And this is a low estimate, because, as noted above, there was still water above the altitude where some of the measurements stopped.

not like others

Eruptions like Mount Pinatubo put a lot of reflective sulfur dioxide aerosols into the stratosphere, and these reflect sunlight back into space. This had a net effect of cooling surface temperatures in the years immediately following the eruption, although the material gradually fell back into the atmosphere, causing the effect to fade over several years. At least in the immediate aftermath, it seems that Hunga Tonga has not produced a similar effect.

Instead, the water vapor was acting as a greenhouse gas, as you would expect. This meant that energy was absorbed by the lower region of the explosion, causing the upper portion to cool by about 2 Kelvin.

Researchers suspect that the enormous amount of water in the explosion prevented sulfur dioxide from ever reaching the stratosphere. And the material that carried it to the heights probably washed away faster. Researchers also suspect that changes in the chemistry of the stratosphere may affect the amount of ozone present there, but it may take longer-term monitoring to resolve this.

Overall, the conclusion appears to be that it really does make a big difference when an underwater explosion occurs. Eruptions such as Hunga Tonga are going to be rare compared to land-based eruptions, because the eruption must occur in relatively shallow water in order to blast material all the way into the stratosphere. But when they do occur, it seems likely that everything from atmospheric chemistry to climate effects is likely to be different.

science2022. DOI: 10.1126/science.abq2299 ,About DOI,

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