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Scientists have described a huge “magma hammer” they say hit the underside of Tonga volcano, which erupted so spectacularly in January.
An analysis of the seismic waves revealed four individual events which are interpreted as the thrusting of molten rock under the seamount.
Each of these blows, occurring over a five-minute period, is estimated to have had a force of one billion tons.
It is yet another revelation about the behavior of Hunga-Tonga Hunga-Ha’apai.
The seamount produced the largest atmospheric explosion ever recorded by modern instrumentation, far larger than even any nuclear test conducted since World War II.
It displaced about 10 cubic km of rock, ash and sediment, much of it exiting the volcano’s vent, or caldera, to shoot skyward, like a “shotgun blast” as one geologist called it.
Scientists gathered here in Chicago at the Fall Meeting of the American Geophysical Union (AGU) to compare the latest results of 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 generated just over 10 minutes after the January 15 climactic eruption.
These signals have been detected by more than 400 monitoring stations around the world.
Dr. Zheng attributes them to a pulse of magma rising from beneath the mountain and hitting the base of the caldera.
“I think it could be like a new batch of magma suddenly reaching the magma chamber and overpressurizing the chamber,” he said. “The pulse of magma is traveling at high speed and it’s like a train hitting the base of the wall. It has hammered four times in 300 seconds,” she told BBC News.
The Hunga-Tonga ash was measured by weather satellites to have traveled 57km above the Earth’s surface, the tallest volcanic plume on record. But new data presented at the AGU meeting indicated that the disturbance went even higher, all the way into space.
Sensors on US Air Force and Space Agency satellites that measure ultraviolet radiation from the Sun have noticed a strong absorption feature in their data that correlates with an altitude above 100 km – the so-called Karman line and the border recognized with space.
‘If I see an absorber, if I see that hole, it means that something has risen above the edge of space and sucked in those photons that would normally be sent to my sensor,’ explained Dr. Larry Paxton, of the Johns Hopkins University Applied Physics Laboratory. “That 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 water sent into space: between 20,000 and 200,000 tons.
That an underwater volcano throws so much water into the sky during an eruption is no surprise. The height to which that water has traveled is, however.
This water also clearly played a role in creating the conditions needed to generate the “largest concentration of lightning ever detected,” according to Chris Vagasky.
Vaisala Inc’s meteorologist works with a network that detects radio frequency emissions associated with lightning strikes. It allows him to locate and count discharges anywhere in the world.
He told the AGU meeting that the Hunga-Tonga eruption plume produced 400,000 lightning strikes on Jan. 15.
“We were getting lightning speeds of up to 5,000 to 5,200 events per minute. That’s orders of magnitude higher than what you’d see in supercell thunderstorms, some of the strongest thunderstorms that exist on this planet,” he said.
“And because these rates were so high, we were saturating our sensors. The number of 400,000 – that’s actually the minimum value. We’re working to figure out how much we’ve been missing.”
One notable consequence of all these lightning strikes is that it produced a burst of gamma rays detected by a NASA satellite that normally looks into the Universe for such high-energy emissions. These came 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 Hunga-Tonga eruption.
