Hunga Tonga-Hunga Ha’apai erupted on January 15 in one of the largest volcanic events in decades, and research in recent years indicates that the volcano produces similar violent eruptions about once every millennium. But some of the deadliest and most explosive eruptions in the last two centuries have come from volcanoes with no historical record of eruption. Now, scientists are taking a fresh look at surprise eruptions and seemingly quiet volcanoes.

Several smaller eruptions have happened at Tonga over the last century, providing some clues for what to expect. But forecasting volcanoes that have been dormant for hundreds or thousands of years is especially challenging. Mount Lamington in Papua New Guinea, for example, killed nearly 3,000 people and displaced thousands more when it erupted for the first time in recorded history in 1951.

“If this were to happen right now, in a region that is highly populated, like, for example, Indonesia or the Philippines, where millions of people live around volcanoes, the consequences for life would be really high,” said Vanesa Burgos, a PhD candidate at Nanyang Technological University (NTU).