Many weather enthusiasts around the world recorded pressure shockwaves from an event in Tonga. The violent eruption of the underwater Hunga-Tonga volcano caused distinctive blips on barographs
Hunga-Tonga-Hunga-Ha’apai Volcanic eruption 2022 NOAA
On the other side of the world on Saturday 15th January GMT a huge volcanic eruption sent shockwaves (pressure waves) around the world allowing many weather observers to record the effects of an event in the Pacific nation of Tonga. The underwater volcano, Hunga-Tonga-Hunga-Ha’apai (HTHH) blew apart its relatively tiny above-water islands. It threw up a huge volcanic ash cloud and caused tsunami waves to reach the main island of Tonga, then travel right across the Pacific basin.
A tidal gauge in Nuku'alofa, the capital of Tonga, measured a 30cm tsunami wave that resulted from the blast. The high water caused coastal flooding and evacuations with communications being knocked out. Rises in sea levels were recorded in New Zealand, Peru , Japan and America, even as far away as Alaska with tsunami warnings around the Pacific Basin. The Australian Met Service BoM had issued a warning for people to move to higher ground on Norfolk Island which recorded a 1.27m high tsunami wave overnight. There were also warnings for the east coast of Australia with rip currents and unusual water surges and currents.
This eruption was one of the most violent ever captured on satellite imagery. Some of the sequences and images have been incredible. Volcanic ash and steam were flung nearly 17,000m (55,000 ft ) up into the air with Volcanic Ash Advisory Centre (VAAC) Wellington overseeing the ash cloud progress for aviation. This ash interfered with early relief efforts from other countries
“The island first formed between Dec. 2014 and Jan. 2015, when an underwater volcano explosively erupted. When all the dust, rock, and ash settled, a newly-formed island remained between two older islands, with a summit reaching 400 feet high. It was the first of its kind to form in 53 years—as well as the first to form during the modern satellite era. Thus, scientists have been able to study its birth and evolution in vivid detail from space. Since its formation, the island has erupted intermittently.” NASA
We are used to seeing seismograph traces from earthquakes, the earth tremors which send the recording pen up and down. Earthquakes usually set off tsunamis but it was the undersea volcano that caused this disturbance. This high energy eruption sent out audible sound to neighbouring islands and lands, water disruption as tsunamis and a powerful air shockwave racing around the earth.
Examples of Barograph readings and blips on Sat 15th from Netweather Forum Volcanic activity thread - Mapantz and BornfromtheVoid
“Pressure is the force per unit area exerted on a surface by the liquid or gas in contact with it. “
In the atmosphere, the pressure at any point on the surface of the earth is equal to the weight of the air above unit area at that location. A barograph is a barometer that records the barometric pressure over time in graphical form. It makes a continuous recording of atmospheric pressure on paper or as output on a computer. It has been these traces that have caused a stir over the weekend.
This push, the ripple of air forced forwards and away from the eruption shows clearly. Imagine a ripple on a pond when a stone is thrown in from height. There are a few crests and troughs in the arc of water that spreads out from the impact. More water in an imagined column above the bottom of the pond, for an instance. Usually a barometer would show steady, smooth traces with only deep low pressures giving a bit of excitement. The Tonga shockwave arrived in the UK during Saturday evening with a distinctive blip and then a less smooth pressure trace continuing over a few hours. If you imagine the shockwave spreading out around the globe, up past Alaska and over the Arctic to the UK and then later, in the early hours of Sunday morning GMT, coming from South Africa, giving a second distinctive blip.
For the people of Tonga, although the tsunami threat has passed, there is damage and disruption. Communications are still poor and the volcanic ash is a health hazard with water supplies also contaminated by sea water. With predicted damage to food crops, relief agencies are looking at support plans. Surveillance flights have started from Australia and New Zealand and power is being restored but the remote nature of these islands means recovery will take time.
Tonga thread in the Netweather community forum
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