Shockwave from Tonga volcanic eruption recorded in Chennai

It presented itself as a sudden spike in the atmospheric pressure

Updated - January 17, 2022 01:00 pm IST

Published - January 17, 2022 11:09 am IST - CHENNAI

A satellite image of the eruption of the underwater volcano.

A satellite image of the eruption of the underwater volcano.

The shockwave generated by the massive volcanic eruption in Tonga in the Pacific Ocean on Saturday, which was felt in many parts of the globe, was recorded in Chennai as well, which is located 12,000 km away.

Watch | Tonga's Underwater Volcano Erupts

It was recorded as a blip in the atmospheric pressure that suddenly spiked by around two hectopascals (hPa) around 8.15 p.m. in Chennai on Saturday, around 10 hours after the eruption happened in Tonga.

The eruption of the submarine volcano, believed to be one of the largest in recent history, took place at 5.15 p.m. local time on Saturday (10.15 a.m. IST), triggering tsunami waves of varying intensity along the coasts of many countries on the Pacific Ocean. Detailed information about its impact on Tonga is yet to emerge as communication remained cut off.


The sound was heard in some places in New Zealand, located roughly 2,500 km away. The Alaska Volcano Observatory in the United States, located more than 9,500 km away from the site of the eruption, reported that a part of the shockwave measured there was in the audible range. The observatory tweeted one of their scientists saying, “The very large signal is not that surprising considering the scale of the eruption, but the audible aspect is fairly unique.”

While it could not be heard in India, it was recorded as a sharp but minor increase in atmospheric pressure.

S. Venkataramanan, a Ph.D scholar from IIT Madras, who has a small weather station installed in his house in West Mambalam, was in the middle of some work when he accidentally noticed that his barometer recordings showed a sudden increase in the atmospheric pressure from 1,012.5 hPa to 1,014.53 hPa around 8.15 p.m. “It looked bizarre. I initially wondered if it was a problem with my equipment,” he said.

While diurnal variations are observed in atmospheric pressure, the changes are in the pattern of a wave and are gradual. A sudden spike and drop were unusual, he said. He immediately reached out to the active weather blogging community in Chennai, who corroborated his readings. “I contacted some from Bengaluru as well, who also recorded the spike. There was a delay of around 20 minutes, which the shockwave took to reach the skies of Bengaluru from Chennai,” he said.

Only then was it confirmed that it was the effect of the shockwave from the Tonga eruption, Mr. Venkataraman added. According to him, the shockwave travelled at a speed of around 1,200 kmph to reach the skies of the city 10 hours after the event.

N. Puviarasan, Director, Area Cyclone Warning Centre, Regional Meteorological Centre, Chennai, said he was alerted on Sunday by his staff who had noticed the blip around the same time. “We were initially surprised as well. Huge winds brought from nearby regions can at times cause the atmospheric pressure to suddenly rise. However, the spike on Saturday looked very different,” he said.

He also concluded that it was the shockwave from Tonga after pulling out reports from different weather stations across the country, all of which showed the spike, albeit with slight differences in time.

“We can compare it with a loud cracker explosion. If we are within a distance of few metres, we feel a gush of air hitting us, which is the shockwave from the explosion,” he said.

“Because of the magnitude of the volcanic eruption, which sent plumes several kilometres high in the air, we are feeling it across the globe. As we are located far away, we neither heard the sound nor felt the shockwave as the change in atmospheric pressure is very small in the range of just 2 hPa recorded by the equipment,” he said. With the Pacific Ocean playing an important role in global weather, the long term impact of volcanic eruptions, if any, has to be studied by experts in the coming days when more details emerge, Mr. Puviarasan added.

Mr. Venkataramanan said the rare event was yet another reminder that nature had no boundaries.

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