THE MAGMA HAMMER STRIKES

Tonga's Recent Massive Underwater Eruption

- Rachel Kehoe

There are more than 1,300 active volcanoes on the planet. Some erupt continuously for many years, while others erupt suddenly with little to no warning. On Jan. 15, 2022, the world was largely caught off guard with the world's most violent volcanic eruption ever recorded with modern instruments. It occurred in Hunga Tonga-Hunga Ha'apai (HUNG-ah TONG-ah-HUNG-ah ha-AHpie), Tonga, in the South Pacific.

But HT-HH, as it's now sometimes called, hadn't really come out of nowhere. This submarine volcano had erupted out of the ocean back in January 2015, creating a new island. The volcano was located 65 kilometers (40 miles) north of Tonga's capital, Nuku'alofa, and joined together two small uninhabited islands called Hunga Tonga and Hunga Ha'apai. That's where the volcano's full name came from. After the 2022 eruption, small pieces of those two islands are the only parts of the volcano that remain above the water.

Though these islands reach only 374 feet (114 meters) above the sea, Hunga Tonga-Hunga Ha'apai is huge. Rising from the seafloor, it measures 1.1 mile (1.8 km) high and 12.4 miles (20 km) wide. The underwater mountain is part of a sweeping arc of volcanoes that form the Tongan part of the Pacific "Ring of Fire."

Volcanic Awakening

Between 2015 and 2021, the volcano erupted occasionally. But these events were considered relatively mild. "They were the kind of eruptions that you could be within a few miles of and still be considered safe," says Kevin Mackay. He is a marine geologist at the National Institute of Water and Atmospheric Research (NIWA) in New Zealand. "There was nothing that would lead us to think a major eruption could even happen," Mackay adds.