Scientists have described a massive “magma hammer” that they said struck the underside of the Tongan volcano that spectacularly erupted in January.
An analysis of the seismic waves revealed four individual events that were interpreted as thrusts of molten rock beneath the mountain underwater.
Over a period of five minutes, the force of each of these strikes was calculated in a billion tons.
It is another revelation of the behavior of the Hunga-Tonga Hunga-Ha’apai.
The seamount produced the largest airburst ever recorded by modern instruments – far larger than even any nuclear bomb test conducted after World War II.
It displaced about 10 cubic kilometers of rock, ash and sediment, much of it escaping through the volcano’s mouth, or caldera, to shoot straight into the sky, like a “gun blast” as one geologist called it.
Scientists gathered here in Chicago for the fall meeting of the American Geophysical Union (AGU) to compare the latest findings of their investigations into what happened.
Dr. Yingcai Zheng, of the University of Houston, detailed his team’s analysis of the 5.8 Magnitude seismic waves generated just over 10 minutes after the Jan. 15 peak eruption.
These signals have been picked up at more than 400 monitoring stations around the world.
Dr. Cheng attributes it to a pulse of magma moving up from the bottom of the mountain and hitting the base of the caldera.
“I think it could be like a new batch of magma that has suddenly arrived in the magma chamber and is putting excessive pressure on the chamber,” he said. He told BBC News: “The magma pulse is moving so fast it’s like a train crashing into the base of a wall. It hits four times in the space of 300 seconds.”
Ash from Hongta Tonga was measured by weather satellites as it traveled 57 kilometers above the Earth’s surface, the highest volcanic plume ever recorded. But new data presented at the AGU meeting indicated that turbulence has spiked even further — all the way into space.
Sensors at the US Space Agency and US Air Force satellites that measure far-ultraviolet radiation from the Sun have noted a strong absorption feature in their data associated with altitudes greater than 100 km – the so-called Karmann line and the recognized frontier of space.
“If you see an absorbent, if you see that pinhole – that means something has risen above the boundary of space and absorbed those photons that would normally be sent to my sensor,” explained Dr. Larry Paxton, of Johns Hopkins University Applied Sciences. Physics lab. “That spot was as big as Montana or Germany or Japan.”
Dr. Paxton could tell by the light signature that the absorber was water vapor, and he could also calculate the mass of the water sent into space: somewhere between 20,000 to 200,000 tons.
That a submarine volcano dumped so much water into the sky during an eruption is not surprising. However, the height that this water traveled is.
This water obviously played a role in creating the conditions needed to generate “the largest concentration of lightning ever discovered,” according to Chris Vagasky.
The meteorologist from Vaisala Inc is working with a network that detects radio frequency emissions associated with lightning events. It enables him to locate and count secretions anywhere in the world.
He told the AGU meeting that the Honga Tonga eruption plume produced 400,000 lightning events on January 15.
“We’ve got lightning rates of 5,000 to 5,200 events per minute. That’s an order of magnitude higher than what you would see in supercell thunderstorms – some of the most powerful thunderstorms on the planet,” he said.
“Because those rates were so high, we were saturating our sensors. The 400,000 figure — that’s actually the value floor. We’re working to figure out how much we missed.”
One notable consequence of all this lightning is that it produced a gamma-ray flash that was detected by a NASA satellite that usually searches the universe for such high-energy emissions. These may come from distant black holes or exploding stars, but this was the first time the Fermi spacecraft had caught a flash coming from a volcano on Earth.
Again, it is a testament to the extreme nature of the Hong Tonga explosion.
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