Ahen the pressure wave from the exploded South Seas volcano raged around the world, Michael Sigl was out and about in the Swiss mountains. No cell phone, no internet, but peace and quiet and the best view over the sea of fog. Just before bed, the Bern atmospheric chemist and paleoclimatologist opened the Twitter app and discovered strange satellite images being posted there. As if in an endless loop, huge clouds of ash shot up over the South Seas, which obviously had to come from a volcano. Then the volcano expert realized what he had missed: the Hunga Tonga-Hunga Ha’apai had blown up a few hours earlier with a great deal of noise. A volcanic explosion that only happens every few decades.
Sigl could hardly sleep that night, he says. He had never seen such satellite photos. And indeed, the eruption was the most violent in thirty years. A similarly spectacular eruption last occurred in June 1991, when Mount Pinatubo in the Philippines spewed nine cubic kilometers of ash and megatons of sulfur dioxide into the atmosphere. This briefly cooled the planet by half a degree. The Hunga Tonga-Hunga Ha’apai also made itself felt worldwide on January 15th. According to reports, it could still be heard in Alaska – and reminded volcanologists of the bang with which Krakatoa between Java and Sumatra blew up in 1883 and triggered a devastating tsunami. It is still considered to be the loudest sound in history.
The eruption column of the Hunga Tonga-Hunga Ha’apai was also huge: It rose up to 39 kilometers into the stratosphere, the second floor of the earth’s atmosphere, and could be observed impressively from space, as well as the lightning fireworks that followed to the explosion occurred. Meter-high tsunamis flooded the coasts of more than a hundred islands in the Kingdom of Tonga, the true extent of the damage and victims remained unclear for a long time. But the tidal waves also piled up on the Pacific coasts from Chile to Japan; Fortunately, there was no major damage there. However, the pressure waves from the explosion, which caused air pressure to fluctuate worldwide, were not felt. “It is very unusual that you can track the sound waves across the globe,” says atmospheric researcher Claudia Timmreck from the Max Planck Institute for Meteorology in Hamburg.
The suffering of the affected people in the island kingdom of Tonga affects Michael Sigl. But from a scientist’s point of view, there was a lot to learn and discover about this eruption at the same time: For the first time such an eruption has been recorded in detail with satellites and modern sensors. Today’s possibilities of remote sensing are fascinating, says Sigl. As a result, today every natural event also becomes a media event. We are virtually there live when a volcano detonates on the other side of the world and a monstrous cloud of ash rises into the sky. The eruption of Tambora, on the other hand, which shook an island that now belongs to Indonesia in 1815 and was an order of magnitude more violent than that of Pinatubo in 1991, was only noticed in Europe and North America when a whole summer was lost there and there were no harvests. This is another reason why the eruption in the Tonga archipelago is so interesting for researchers like Michael Sigl: As a paleoclimatologist, he is chasing traces of volcanic eruptions that have long since subsided. In painstaking detail work, he looks for legacies of the eruptions in ice cores from Greenland and Antarctica – and estimates their influence on the global climate. Now he could watch an eruption and its effects in near real time.