Acoustic waves caused by the eruption of the Tonga volcano detected in the Pyrenees

Last Saturday, January 15, the underwater volcano on the island of Tonga erupted and its effects have spread to various parts of the planet. In Spain, in the Pyrenees, acoustic waves caused by this phenomenon have been detected, as reported by the CSIC.

From the volcano of La Palma to the volcano of Tonga: the differences between two devastating eruptions

From the volcano of La Palma to the volcano of Tonga: the differences between two devastating eruptions

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The waves produced by the eruption travel at about 8 km/s, so they reached the Pyrenees 20 minutes after the explosion. 16 hours later, the arrival of the pressure wave occurs, causing a deformation clearly detected by the seismometer.

The CSIC says that there were two acoustic signals that arrived. The first wave, after traveling the shortest path between Tonga and the Pyrenees, arrives at the seismic station around 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.

The most interesting point of the data obtained in the LSC is that they allow identifying the deformation of the ground produced by the second passage, some 36 hours later, of the pressure waves, which reach the Pyrenees after having circled the Earth again and traveled a total of 57,000 km, still being able to generate a clearly perceptible signal.

Saturday, when the Tonga volcano erupted, caused a tsunami in the Pacific, a volcanic plume about 30 kilometers high and a strong explosion. The latter has had an energy of about 10 megatons, according to NASA, something that translates, says the CSIC, into an energy 500 times higher than that of the Hiroshima nuclear bomb of World War II.

The effects have been distributed throughout the planet, moving like a shock wave, with a speed of close to 1,100 km/h. The pressure variations as the wave passes generally range between 1 and 8 millibars. That variation has caused changes in sea level at different points. In Spain, it has affected towns on the coasts of Valencia and the Balearic Islands, with variations of 50 centimeters in height.

The ground deformation produced by the associated pressure variation can also be detected by seismic sensors, whose main objective is the recording of 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 CSIC's GEO3BCN institute, show a particularly interesting example of this type of recording. This seismic station is located about 17,000 km from the volcano, relatively close to its antipodal point, located in southern Algeria.

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. However, the seismic detection of the ground deformation produced by the second passage of the acoustic waves is an exceptional event, which highlights the great energy of the explosion.

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