Iojima Island in Japan sits underwater on the edge of the giant Kikai-Akahoya volcanic caldera.

Iōjima Island, itself a volcano, sits underwater on the rim of the giant Kikai-Akahoya volcanic caldera.

Asahi Shimbun via Getty Images

The largest volcanic eruption of the current geologic era occurred underwater off the southern coast of Japan about 7,300 years ago. This explosion produced three times as much material as the largest modern explosion. Tambora mountainwhich erupted in Indonesia in 1815 and caused such drastic climate changes that it caused 1816 to become the “year without a summer”.

The new record holder, the Kikai-Akahoya eruption, came from a submerged caldera in an area of ​​the ocean near the Japanese island of Kyushu.

The eruption’s devastating consequences for humans living on nearby islands have been documented by geologists and archaeologists, and analysis of volcanic ash deposits indicates that the eruption was the longest of the current geologic era, the Holocene. There was one of the major eruptions, which began 11,700 years ago. .

However, the origin and size of the eruption were uncertain due to the difficulty of accessing the submarine caldera, the crater formed after the eruption, and the volcanic deposits on the sea floor.

now, Nobukazu Sima At Kobe University in Japan and colleagues have calculated that the Kikai-Akahoya eruption produced a much larger amount of rock and ash underwater than previously thought, at about 70 cubic kilometers. Combining this with previous estimates of volcanic rock deposited on Japan, the total amount of material ejected from the volcano equates to more than 300 cubic kilometers of material. That’s twice the amount of water in Lake Tahoe in the western United States. “It’s quite big, more than we expected,” says Seema.

It still lags significantly. A massive eruption of the Toba supervolcano in Indonesia about 74,000 years agoHowever, that released more than 2500 cubic kilometers of magma.

To assess Kikai-Akahoya, Seama and his colleagues conducted a seismic survey to map the underwater area around the caldera about 200 meters below the surface. From this, they could see the layers of material around the volcano, but they didn’t know what was from the eruption itself.

So the researchers used a remote-controlled drilling robot to collect deposits from the sea floor and take core samples from the underlying rock, identifying the layer that contained the specific volcanic glass. The data allowed them to isolate the volcanic crust from seismic surveys and calculate the total volume of volcanic material.

“We know that these very large, caldera-shaped eruptions are rare, but we also know that there are more of them in the geological past than we have evidence for,” he says. David Pyle At Oxford University

He says the biggest obstacle to determining the size of an eruption so far is that it’s difficult to find and measure calderas that lie deep underwater.

The Kikai-Akahoya caldera still has a Large magma chamber below it. Seema says that if it erupts, it could have another eruption, but we don’t know how big it will be because it depends on the size of the magma chamber. Although the chances of it exploding are low, he says, his team is working on more precise measurements of the dome to improve our understanding of the risk.

Combining historical information from past eruptions such as Kikai-Akahoya with studies of more recent underwater eruptions, e.g. Hanga Tonga Eruption in 2022That could help us develop better models to predict future outbreaks, Pyle says.