7,300 years ago saw the largest volcanic eruption in recorded history.

The largest volcanic eruption in current geological time occurred underwater off the southern coast of Japan about 7,300 years ago. This explosion produced more than three times as much material as the eruption of Mount Tambora, the largest known modern eruption. Mount Tambora exploded in Indonesia in 1815, causing dramatic climate changes that led to the “Year Without a Summer” in 1816.

The new record holder, the Kikai Akahoya eruption, originated from a submerged caldera in an area off Japan's Kyushu island.

The devastating impact this eruption had on humans living on nearby islands has been recorded by geologists and archaeologists, and analysis of volcanic ash deposits has shown that this eruption was the most recent geological event that began 11,700 years ago. It was shown to be one of the largest eruptions of the Holocene era. .

However, the origin and scale of the explosion were unclear because of the difficulty in accessing the submarine caldera, the crater formed after the volcanic eruption, and the volcanic deposits on the ocean floor.

now, Nobukazu Sema Professors at Japan's Kobe University calculated that the Kikai-Akahoya eruption produced far more rock and ash underwater than previously thought, about 70 cubic kilometers. Combining this with previous estimates from volcanic rocks deposited over Japan, the total amount of material pumped out of the volcano equates to more than 300 cubic kilometers of material. This is twice the amount of water in Lake Tahoe in the western United States. “It was huge, more than we expected,” Seema says.

However, it is still far behind the huge eruption of Indonesia's Toba supervolcano, which released more than 2,500 cubic kilometers of magma about 74,000 years ago.

To assess Kikai Akahoya, Seema and his colleagues conducted seismic surveys and mapped the underwater area around the caldera, about 200 meters below the surface. This allowed them to see layers of material around the volcano, but they could not tell which ones were due to the eruption itself.

The researchers used remote-controlled drilling robots to collect sediment from the ocean floor, take core samples from the underlying rock, and identify layers containing characteristic volcanic glass. This data allowed us to isolate the volcanic layers from seismic surveys and calculate the total amount of material produced by the volcano.

“We know that very large, caldera-forming eruptions like this are rare, but we also know that there have been many more of these events in the geological past, and we have found evidence for them. ” he says. David Pyle at Oxford University.

The main reason it took so long for the scale of the eruption to be determined is because calderas deep under the sea are difficult to locate and measure, he said.

It still remains in the Kikai Akahoya caldera. big magma chamber It's below. If this explodes, there could be another eruption, but it's unclear how big it will be because it depends on the size of the magma chamber, Seema said. He says the chance of an eruption is small, but his team is working on measuring the dome more precisely to better understand the risks.

Creating better models to predict future eruptions by combining historical information from past eruptions, such as the Kikai-Akahoya eruption, with research from recent underwater eruptions, such as the 2022 Hunga-Tonga eruption. Pyle says it could help.