Last year, an immense but brief outburst of seismic energy was soon followed by a long hum that made the world ring. Finding its cause took 68 scientists and an assist by the Danish military.
On September 16, 2023, the world began to rumble.A gargantuan rock-ice avalanche tumbled into the deep waters of a fjord in eastern Greenland, unleashing a megatsunami whose initial waves reached a height of 200 meters. The waves scoured the walls of the fjord before flowing into the open sea.Even for this avalanche-prone corner of Greenland, the collapse and subsequent megatsunami were shocking for their speed and ferocity. But what followed was considerably stranger. The collapse trigged a monotonous growl that kept going for nine days straight. It was strong enough to be detected by seismometers all around the world. And yet, when the Danish military visited the scene, they found nothing amiss.“This is crazy,” said Kristian Svennevig(opens a new tab), a geologist at the Geological Survey of Denmark and Greenland and a member of a team that investigated the anomaly. It was like nothing anyone had ever seen.“Immediately, there was a massive amount of researchers joining forces,” said Finn Løvholt(opens a new tab), a tsunami and landslide researcher at the Norwegian Geotechnical Institute in Oslo. The team quickly grew to include experts from 15 different countries. The Danish navy offered their help. But nothing anyone suggested as an underlying cause — from peculiar magmatic movements to jiggling ice sheets — seemed to make sense.“If we found no other explanation, we would have gone for sea monster or baby dragons,” joked team member Stephen Hicks(opens a new tab), a seismologist at University College London.Now, as reported today in the journal Science(opens a new tab), a team of 68 scientists has managed to identify the source of the world-wobbling hum: a bizarre natural phenomenon, rhythmically hammering on Earth’s surface like a drum.“I don’t know if anyone’s seen anything even remotely like that before,” said Ben Fernando(opens a new tab), a seismologist at Johns Hopkins University who was not involved with the new study. “It’s a very cool result.”The joy of discovering something so outlandish has left the team both humbled and overjoyed. “This is probably why a lot of these people went into science,” Svennevig said. “With all our fancy gear and equipment and knowledge, we still, once in a while, find something [we] don’t know.”