Tonga Eruption Detection

An Eccentric Anomaly: Ed Davies's Blog

Volcanic eruption detected in Dunbeath!

This morning, while eating breakfast, I watched Scott Manley's video Volcanic Eruption May Be Biggest Ever Seen From Space which, amongst other things, talks about detections of the pressure wave from the event around the world including the ripple of changes in pressure seen by weather stations as the wave crossed the US and a 2.5 hPa fluctuation seen in Switzerland.

Hmmm, I log the pressure in my bedroom every just over 2 minutes with a resolution of better than 0.1 hPa. I wonder…

According to this tweet by the Comprehensive Test Ban Treaty Organization, found via Scott's video, the major eruption happened at 2022-01-15T04:15Z and, according to Scott's video the pressure wave was seen at Half Moon Bay in California, just west of Silicon Valley, at 04:00 PST, 2021-01-15T12:00Z so 7h45m after the eruption. Half Moon Bay is 8509 km from Hunga Tonga so that gives a speed of 305 m/s. I.e., pretty much the speed of sound in air as you'd expect but worth checking for things happening on this sort of scale.

Dunbeath is 15'790 km from Hunga Tonga (over a thousand km closer than the centre of Switzerland, which might be a bit surprising to those brought up on the Mercator projection but the great circle route to either from Tonga is pretty close to over the North Pole) so the travel time would be 14h23m giving an arrival time of around 2022-01-15T18:38Z.

Both the Half Moon Bay and the Swiss graphs show a peak then a trough in the pressure. The timescale is visible on the Half Moon Bay graph showing an event lasting about half an hour. Twice as far away in Dunbeath it would not be unreasonable to expect the whole thing to be spread out to about an hour in length.

Here's my pressure graph for Dunbeath on the 15th, times local and UTC (they're the same in winter), links to bigger version as usual:

Yep, I'm calling that a detection. Maybe a few minutes later than calculated but that was pretty rough.

Shorter timescale:

Update: 2022-01-16T13:25:00Z Other detections.

Update: 2022-01-16T13:45:00Z From the fedi-thread linked above comes the idea of looking for the other pressure wave, the one that went the long way round: south from Tonga, across Antarctica then up the Atlantic to Dunbeath. That's 24'236 km so at 305 m/s should take 22h4m giving an arrival time around 2022-01-16T02:19Z.

Not so clear cut but definitely yep!