The most important volcanic eruption of the present geological epoch occurred underwater off the southern coast of Japan about 7300 years in the past. The blast produced greater than 3 times as a lot materials as the biggest fashionable eruption identified, that of Mount Tambora, which exploded in Indonesia in 1815 and prompted such drastic local weather adjustments that it led to the “12 months With no Summer season” in 1816.

The brand new record-holder, the Kikai-Akahoya eruption, got here from a submerged caldera in a area of sea close to the Japanese island of Kyushu.

The eruption’s devastating penalties for people residing on close by islands have been documented by geologists and archaeologists, and evaluation of deposits of volcanic ash had indicated that the blast was one of many largest eruptions of the present geological epoch, the Holocene, which started 11,700 years in the past.

Nonetheless, the blast’s origins and dimension had been unsure due to the issue in accessing the undersea caldera, the crater that shaped after the volcano erupted, and volcanic deposits on the seabed.

Now, Nobukazu Seama at Kobe College in Japan and his colleagues have calculated that the Kikai-Akahoya eruption produced a far bigger quantity of rock and ash underwater than beforehand thought, at round 70 cubic kilometres. Combining this with earlier estimates from volcanic rock deposited over Japan, the overall quantity of fabric pumped out from the volcano equates to greater than 300 cubic kilometres of fabric. That is equal to twice the quantity of water in Lake Tahoe within the western US. “It’s fairly large, greater than we anticipated,” says Seama.

It’s nonetheless considerably behind the huge eruption of the Toba supervolcano in Indonesia some 74,000 years in the past, although, which launched greater than 2500 cubic kilometres of magma.

To evaluate Kikai-Akahoya, Seama and his colleagues did a seismic survey to map out the underwater area across the caldera roughly 200 metres under the floor. From this, they may see the layers of fabric across the volcano, however they didn’t know which had been from the eruption itself.

So the researchers collected deposits from the ocean ground utilizing a remote-controlled drilling robotic and took core samples from the rock under, figuring out a layer that contained distinctive volcanic glass. The info allowed them to isolate the volcanic layer from the seismic survey and calculate the overall quantity of fabric that the volcano produced.

“We all know that these very giant, caldera-forming eruptions are uncommon, however we additionally know that there are extra of those occasions within the geological previous that we’ve discovered proof for,” says David Pyle on the College of Oxford.

The primary cause that the eruption’s dimension has taken till now to be decided is as a result of it’s tough to search out and measure calderas that lie deep underwater, he says.

The Kikai-Akahoya caldera nonetheless has a large magma chamber beneath it. If this explodes, it may produce one other eruption, however we don’t know the way giant it might be as a result of it depends upon the scale of the magma chamber, says Seama. Whereas the possibilities of it erupting are small, he says, his group is engaged on measuring the dome extra precisely to enhance our understanding of the chance.

Combining historic data from previous eruptions like Kikai-Akahoya with research of newer underwater eruptions, such because the Hunga Tonga eruption in 2022, may assist us produce higher fashions for predicting future eruptions, says Pyle.