Scientists have described a massive “magma hammer” they say hit the underside of the Tonga volcano that erupted so spectacularly in January.
An analysis of the seismic waves revealed four individual events which are interpreted as surges of molten rock beneath the seamount.
Occurring within a period of five minutes, each of these blows would have had a force of one billion tons.
This is another revelation about the behavior of the Hunga-Tonga Hunga-Ha’apai.
The seamount produced the largest atmospheric explosion ever recorded by modern instrumentation – far larger even than any nuclear bomb test conducted after World War II.
It moved about 10 km3 of rock, ash and sediment, much of it exiting the mouth of the volcano, or caldera, to soar straight into the sky, like a “shotgun blast”, as called him a geologist.
Scientists gathered here in Chicago at the American Geophysical Union (AGU) fall meeting 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 magnitude 5.8 seismic waves generated just over 10 minutes after the January 15 climate eruption.
These signals were picked up at more than 400 monitoring stations around the world.
Dr Zheng attributes them to a pulse of magma rising from below the mountain and hitting the base of the caldera.
“I think it could be like a new batch of magma suddenly hitting the magma chamber and overpressurizing the chamber,” he said. “The pulse of the magma is rising at high speed and it’s like a train hitting the base of the wall. It pounded four times in 300 seconds,” he told BBC News.
The Hunga-Tonga ash was measured by weather satellites to have traveled 57 km above the Earth’s surface, the highest volcanic plume on record. But new data presented at the AGU meeting indicated that the disturbance was even higher – up to space.
Sensors from US Space Agency and US Air Force satellites that measure far ultraviolet radiation from the Sun have noticed a strong absorption feature in their data correlated to an altitude above 100 km – the so-called line Karman and the recognized boundary with space.
“If I see an absorber, if I see this hole – it means 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. “This place was as big as Montana, or Germany, or Japan.”
Dr. Paxton can tell from the light signature that the absorber was water vapour, and he can also calculate the mass of water sent into space: between 20,000 and 200,000 tons.
That an underwater volcano shoots so much water into the sky during an eruption is no surprise. How high this water has traveled is, however.
This water also clearly played a role in creating the conditions necessary to generate the “greatest 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. It allows him to locate and count releases anywhere on the globe.
He told the AGU meeting that the Hunga-Tonga eruption plume produced 400,000 flashes on January 15.
“We were getting lightning rates of up to 5,000 to 5,200 events per minute. That’s an order of magnitude greater than what you would see in supercell thunderstorms – some of the most powerful thunderstorms that exist on this planet. “, did he declare.
“And because those rates were so high, we’re overloading our sensors. The 400,000 number – that’s actually the bottom of the value. We’re working to figure out how much we missed.”
A remarkable consequence of all these flashes is that they produced a flash of gamma rays detected by a Nasa satellite which normally looks out into the Universe for these high energy emissions. These are believed to come from distant black holes or exploding stars, but this was the first time the Fermi spacecraft had picked up lightning from a volcano on Earth.
Again, this speaks to the extreme nature of the Hunga-Tonga eruption.