May 17, 2022 5:08 pm

Sound waves from the eruption of the Tonga volcano in the Pyrenees

Francis Martin Leon 5 min
GOES-17 10.35 µm channel enhanced infrared image. Credit: Tim Schmit, NOAA/NESDIS/ASPB – CIMSS

On January 15 around 04:00 (UTC) the underwater volcano Hunga-Tonga-Hunga-Ha’apai erupted causing a tsunami in the Pacific Ocean, a volcanic plume nearly 30 km high and a strong explosion, whose energy has been estimated by NASA at about 10 megatons, about 500 times greater than the nuclear bomb exploded in Hiroshima during world war II.

The variation in atmospheric pressure generated by this explosion has spread throughout the planet, moving like a shock wave, with a speed close to 1100 km/h. This wave has been detected by various types of sensors, such as barometers integrated in weather stations, infrasound sensors or geodetic stations. The pressure variations at the passage of the wave generally range between 1 and 8 millibars.

The sudden pressure variation produced at the arrival of this wave has caused variations in sea level in many places on the planet, including locations on the coasts of Valencia and the Balearic Islands, reaching variations of 50 cm in height.

Seismic waves

The ground deformation produced by the associated pressure variation can also be detected by seismic sensors, whose main objective is to record the seismic waves generated by earthquakes. The data obtained by the seismic sensor installed in the Canfranc Underground Laboratory (LSC) and managed through a collaboration agreement by the GEO3BCN institute of the CSIC, show an example of special interest of this type of records. This seismic station is located about 17,000 km from the volcano, relatively close to its antipodal point, located in southern Algeria.

First of all, the seismometer registers the arrival of the seismic waves produced by the eruption. These waves travel at speeds close to 8 km/s (28.8 km/h), reaching the Pyrenees about 20 minutes after the explosion.. About 16 hours later, the arrival of the pressure wave occurs, causing a deformation clearly detected by the seismometer.

Analyzing the data in more detail, it can be identify the arrival of two acoustic signals.

The first wave, after traveling along the shortest route between Tonga and the Pyrenees, arrives at the seismic station near the 20:00 UTC. About four hours later, the arrival of the acoustic wave that had traveled the balloon in the opposite direction, thus following a longer path, is recorded..

Although the signals can be identified in the three components of the seismic records, their identification is clearer in the North-South oriented component (HHN), since the waves reach the Pyrenees in this direction.

The most interesting point of the data obtained in the LSC is that allow to identify the soil deformation produced by the second step, some 36 hours later, from the pressure waves, which reach the Pyrenees after having circumnavigated the Earth again and traveled a total of 57,000 km, still capable of generating a clearly perceptible signal.

When large earthquakes occur, the generated surface waves circumnavigate the planet, taking about 3.5 hours for each turn. It is relatively common to detect two or three of these steps in seismic sensors located in areas with little ambient noise. But nevertheless, seismic detection of ground deformation produced by the second pass of acoustic waves is an exceptional event, which highlights the great energy of the explosion.

19 January, 2022


This entry was published in News on 20 Jan 2022 by Francisco Martín León

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