Tonga volcano: Plume reached half-way to space

An indicator of the great power of last Saturday’s volcanic eruption in Tonga is the height reached by its plume.

UK scientists examining weather satellite data calculate it to be around 55km (35 miles) above the Earth’s surface.

This is at the boundary of the stratosphere and mesosphere layers in the atmosphere.

Dr Simon Proud, from RAL Space, said these were “unheard-of altitudes” for a volcanic plume.

The most powerful eruption in the second half of the 20th Century came from Mount Pinatubo in 1991. Its plume is thought to have climbed to roughly 40km.

However, it’s possible today’s more accurate satellites would have given a higher altitude for the Philippines event, cautioned Dr Proud, who is affiliated to the UK National Centre for Earth Observation.

Ash in the atmosphereIMAGE SOURCE,NASA
Image caption,

The spreading ash was visible from the International Space Station

To work out the position in the sky of the plume from Tonga’s Hunga-Tonga Hunga-Ha’apai volcano, data from three weather satellites – Himawari-8 (Japan) GOES-17 (USA) and GK2A (Korean) – was used.

“Because they’re all at different longitudes, we can use the parallax between their views of the eruption to determine altitude. This is a pretty well established technique for storm cloud heights, and should actually work better here as the altitude [and hence parallax] is greater,” Dr Proud said.

Only a small part of the cloud is seen to get to 55km. This is most likely water vapour, rather than ash, that was pushed upward at the head of the updraft. The main umbrella of the plume is at 35km. A lower plume feature is evident in the lowest layer of the atmosphere – the troposphere.

The so-called Kármán line, which is often quoted as the atmospheric boundary with outer space, is at 100km.

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