Tongan volcano pressure wave felt in Penallt!

The underwater Hunga Tonga-Hunga Ha'apai eruption near Tonga took place at 5.40 am (GMT) last Saturday (15th January), the explosion setting off a sonic boom which was heard for many miles.

The massive pressure wave which caused the boom would have been felt over large distances from the centre, one question now being just how far did it travel? Did it get to Penallt for instance, a distance of 10275 miles?

Well, the pressure wave travels at Mach 1, the speed of sound, which is 761 mph. So the time taken for 10275 miles would be 10275/761 = 13.5 hours.

And 13.5 hours after 5.40 am would be 7.10 pm, or 7 pm to the nearest half-hour.

And the Penallt weather station barograph (which records atmospheric pressure on the half-hour) does indeed show a spike at exactly this time, together with associated pressure “wobbles” for the following 8 hours. So, yes, the pressure wave from the Tongan volcano was “felt” in Penallt, but the pressure front had diffused so much over its long journey that there was no longer anything like a sharp shock when it got here.