The eruption of the Tonga volcano continues to amaze
The expanding plume on January 15th
Scientists have described a massive "magma hammer" they say slammed into the underside of the Tonga volcano that erupted so spectacularly in January.
An analysis of seismic waves has revealed four separate events that are interpreted as bursts of molten rock beneath the seamount.
Each of these strikes, which took place within five minutes, had a calculated force of one billion tons.
It is another revelation about the behavior of Hunga-Tonga Hunga-Ha'apai.
The seamount produced the largest atmospheric explosion ever recorded by modern instruments – far larger even than any atomic bomb test conducted after World War II.
It displaced about 10 cubic kilometers of rock, ash, and sediment, much of which exited through the volcano's mouth or caldera to blast straight into the sky, like what one geologist called a "shotgun blast."
The Hunga Tonga caldera is now a 850 m deep hole
Scientists have gathered here in Chicago at the American Geophysical Union (AGU) fall meeting to compare the latest results from their investigations into what happened.
dr Yingcai Zheng of the University of Houston detailed his team's analysis of the magnitude 5.8 seismic waves, which were generated just over 10 minutes after the eruption peaked on Jan. 15.
These signals were received at more than 400 monitoring stations around the world.
dr Zheng attributes them to a magma pulse moving up from beneath the mountain and hitting the base of the caldera.
"I think it could be like a new charge of magma suddenly grabbing into the magma chamber and overpressurizing the chamber," he said. "The pulse of magma is moving upwards at high speed, and it's like a train hitting the base of the wall. He hammered four times in 300 seconds," he told BBC News.
Ash from Hunga-Tonga has been measured by weather satellites to have migrated 57 km above the surface of the earth, the highest volcanic plume ever recorded. But new data presented at the AGU meeting showed the disruption went even higher – into space.
The story goes on
Sensors on US Space Agency and US Air Force satellites that measure the Sun's far-ultraviolet radiation noticed a strong absorption feature in their data that correlates with an altitude above 100 km — the so-called Karman line and the accepted limit to the Sun Space.
"If I see an absorber, if I see this hole, it means something has stepped over the edge of space and sucked up these photons that would normally be sent to my sensor," explained Dr. Larry Paxton from the Johns Hopkins University Applied Physics Laboratory. "This place was as big as Montana or Germany or Japan."
dr Paxton can tell from the light signature that the absorber was water vapor, and he can also calculate the mass of the water sent into space: somewhere between 20,000 and 200,000 tons.
The "hole" (white arrow) in the UV data is explained by the presence of water above 100 km
It's no surprise that an undersea volcano should erupt so much water into the sky. However, the height to which this water traveled is.
According to Chris Vagasky, this water also clearly played a role in creating the conditions necessary to produce the "largest concentration of lightning ever discovered".
Vaisala Inc's meteorologist works with a network that detects the radio frequency emissions associated with lightning events. It allows him to locate and count discharges anywhere in the world.
He told the AGU meeting that the Jan. 15 Hunga-Tonga plume produced 400,000 lightning events.
"We've had flash rates of up to 5,000 to 5,200 events per minute. That's an order of magnitude higher than supercell thunderstorms — some of the most powerful thunderstorms on the planet," he said.
"And because those rates were so high, we saturated our sensors. The number 400,000 – that is actually the lower limit of the value. We are working to find out how much we missed."
A notable consequence of all these flashes is that they produced a gamma-ray burst, which was spotted by a Nasa satellite that normally looks out into the universe for such high-energy emissions. These would come from distant black holes or exploding stars, but this was the first time the Fermi spacecraft had captured lightning coming from a volcano on Earth.
This too is evidence of the extreme nature of the Hunga Tonga eruption.
Graphic with a map of Tonga and a satellite image showing the extent of the ash plume just after the eruption.
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