Highest volcanic plume on Earth

On 15 January 2022, the submarine Hunga Tonga-Hunga Ha’apai volcano – located near the island of Tonga in the Pacific Ocean – erupted, generating a plume that reached an altitude of some 57 kilometres (36 miles). It was the first volcanic plume known to have penetrated the mesosphere, the third layer of the atmosphere, which extends from around 50 to 80 kilometres (31–128 miles) above Earth. Scientists at NASA’s Langley Research Center calculated the height of the plume – a mixture of volcanic gas, ash, smoke, steam and particulate debris – based on satellite data.

The Hunga Tonga-Hunga Ha’apai event has been cited as the largest recorded eruption since that of Krakatoa in Indonesia in 1883 and its plume was 22.5 km (14 mi) higher than the previous record, set by Mount Pinatubo in the Philippines 1991. At one point, the volcanic thunderstorm that resulted produced a record 200,000 lightning strikes in just one hour. It also triggered currents that propelled ash, gas and rocks across the seabed at 122 km/h (76 mph) – the fastest undersea volcanic flow. They travelled at least 100 km (62 mi) across the seabed, generated a huge tsunami, and inflicted widespread damage to submarine telecommunications cables.

Plumes from thunderstorms and volcanic eruptions usually halt at the tropopause – the lowest of the five layers in Earth’s atmosphere. Air temperature in the next layer, the stratosphere, increases with altitude and most updrafts cannot penetrate it. Only significantly hotter or more explosive volcanic plumes extend beyond the tropopause.

The sound of the eruption was heard in Alaska, USA, some 8,050 km (5,000 mi) away. Although the resultant megatsunami devastated some parts of Tonga, there were only a handful of fatalities. The surprisingly low loss of life has been attributed to several factors, including the rapid reaction of the local communities and low tourist numbers owing to the COVID-19 pandemic. Tonga’s main city, Nuku’alofa, was protected by its location behind an island in a lagoon, although the megatsunami – which generated waves that peaked at a height of around 90 m (295 ft) – caused the deaths of two people in Peru, around 10,000 km (6,200 mi) away.